Merge tag 'md-3.5' of git://neil.brown.name/md

Pull md updates from NeilBrown:
 "It's been a busy cycle for md - lots of fun stuff here..  if you like
  this kind of thing :-)

  Main features:
   - RAID10 arrays can be reshaped - adding and removing devices and
     changing chunks (not 'far' array though)
   - allow RAID5 arrays to be reshaped with a backup file (not tested
     yet, but the priciple works fine for RAID10).
   - arrays can be reshaped while a bitmap is present - you no longer
     need to remove it first
   - SSSE3 support for RAID6 syndrome calculations

  and of course a number of minor fixes etc."

* tag 'md-3.5' of git://neil.brown.name/md: (56 commits)
  md/bitmap: record the space available for the bitmap in the superblock.
  md/raid10: Remove extras after reshape to smaller number of devices.
  md/raid5: improve removal of extra devices after reshape.
  md: check the return of mddev_find()
  MD RAID1: Further conditionalize 'fullsync'
  DM RAID: Use md_error() in place of simply setting Faulty bit
  DM RAID: Record and handle missing devices
  DM RAID: Set recovery flags on resume
  md/raid5: Allow reshape while a bitmap is present.
  md/raid10: resize bitmap when required during reshape.
  md: allow array to be resized while bitmap is present.
  md/bitmap: make sure reshape request are reflected in superblock.
  md/bitmap: add bitmap_resize function to allow bitmap resizing.
  md/bitmap: use DIV_ROUND_UP instead of open-code
  md/bitmap: create a 'struct bitmap_counts' substructure of 'struct bitmap'
  md/bitmap: make bitmap bitops atomic.
  md/bitmap: make _page_attr bitops atomic.
  md/bitmap: merge bitmap_file_unmap and bitmap_file_put.
  md/bitmap: remove async freeing of bitmap file.
  md/bitmap: convert some spin_lock_irqsave to spin_lock_irq
  ...

10 files changed, 2365 insertions, 795 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 17e2b472e16..15dbe03117e 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -45,7 +45,7 @@ static inline char *bmname(struct bitmap *bitmap)
  * if we find our page, we increment the page's refcount so that it stays
  * allocated while we're using it
  */
-static int bitmap_checkpage(struct bitmap *bitmap,
+static int bitmap_checkpage(struct bitmap_counts *bitmap,
 			    unsigned long page, int create)
 __releases(bitmap->lock)
 __acquires(bitmap->lock)
@@ -76,8 +76,7 @@ __acquires(bitmap->lock)
 	spin_lock_irq(&bitmap->lock);
 
 	if (mappage == NULL) {
-		pr_debug("%s: bitmap map page allocation failed, hijacking\n",
-			 bmname(bitmap));
+		pr_debug("md/bitmap: map page allocation failed, hijacking\n");
 		/* failed - set the hijacked flag so that we can use the
 		 * pointer as a counter */
 		if (!bitmap->bp[page].map)
@@ -100,7 +99,7 @@ __acquires(bitmap->lock)
 /* if page is completely empty, put it back on the free list, or dealloc it */
 /* if page was hijacked, unmark the flag so it might get alloced next time */
 /* Note: lock should be held when calling this */
-static void bitmap_checkfree(struct bitmap *bitmap, unsigned long page)
+static void bitmap_checkfree(struct bitmap_counts *bitmap, unsigned long page)
 {
 	char *ptr;
 
@@ -130,22 +129,14 @@ static void bitmap_checkfree(struct bitmap *bitmap, unsigned long page)
  */
 
 /* IO operations when bitmap is stored near all superblocks */
-static struct page *read_sb_page(struct mddev *mddev, loff_t offset,
-				 struct page *page,
-				 unsigned long index, int size)
+static int read_sb_page(struct mddev *mddev, loff_t offset,
+			struct page *page,
+			unsigned long index, int size)
 {
 	/* choose a good rdev and read the page from there */
 
 	struct md_rdev *rdev;
 	sector_t target;
-	int did_alloc = 0;
-
-	if (!page) {
-		page = alloc_page(GFP_KERNEL);
-		if (!page)
-			return ERR_PTR(-ENOMEM);
-		did_alloc = 1;
-	}
 
 	rdev_for_each(rdev, mddev) {
 		if (! test_bit(In_sync, &rdev->flags)
@@ -158,15 +149,10 @@ static struct page *read_sb_page(struct mddev *mddev, loff_t offset,
 				 roundup(size, bdev_logical_block_size(rdev->bdev)),
 				 page, READ, true)) {
 			page->index = index;
-			attach_page_buffers(page, NULL); /* so that free_buffer will
-							  * quietly no-op */
-			return page;
+			return 0;
 		}
 	}
-	if (did_alloc)
-		put_page(page);
-	return ERR_PTR(-EIO);
-
+	return -EIO;
 }
 
 static struct md_rdev *next_active_rdev(struct md_rdev *rdev, struct mddev *mddev)
@@ -208,6 +194,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 	struct md_rdev *rdev = NULL;
 	struct block_device *bdev;
 	struct mddev *mddev = bitmap->mddev;
+	struct bitmap_storage *store = &bitmap->storage;
 
 	while ((rdev = next_active_rdev(rdev, mddev)) != NULL) {
 		int size = PAGE_SIZE;
@@ -215,9 +202,13 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 
 		bdev = (rdev->meta_bdev) ? rdev->meta_bdev : rdev->bdev;
 
-		if (page->index == bitmap->file_pages-1)
-			size = roundup(bitmap->last_page_size,
+		if (page->index == store->file_pages-1) {
+			int last_page_size = store->bytes & (PAGE_SIZE-1);
+			if (last_page_size == 0)
+				last_page_size = PAGE_SIZE;
+			size = roundup(last_page_size,
 				       bdev_logical_block_size(bdev));
+		}
 		/* Just make sure we aren't corrupting data or
 		 * metadata
 		 */
@@ -276,10 +267,10 @@ static void write_page(struct bitmap *bitmap, struct page *page, int wait)
 {
 	struct buffer_head *bh;
 
-	if (bitmap->file == NULL) {
+	if (bitmap->storage.file == NULL) {
 		switch (write_sb_page(bitmap, page, wait)) {
 		case -EINVAL:
-			bitmap->flags |= BITMAP_WRITE_ERROR;
+			set_bit(BITMAP_WRITE_ERROR, &bitmap->flags);
 		}
 	} else {
 
@@ -297,20 +288,16 @@ static void write_page(struct bitmap *bitmap, struct page *page, int wait)
 			wait_event(bitmap->write_wait,
 				   atomic_read(&bitmap->pending_writes)==0);
 	}
-	if (bitmap->flags & BITMAP_WRITE_ERROR)
+	if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
 		bitmap_file_kick(bitmap);
 }
 
 static void end_bitmap_write(struct buffer_head *bh, int uptodate)
 {
 	struct bitmap *bitmap = bh->b_private;
-	unsigned long flags;
 
-	if (!uptodate) {
-		spin_lock_irqsave(&bitmap->lock, flags);
-		bitmap->flags |= BITMAP_WRITE_ERROR;
-		spin_unlock_irqrestore(&bitmap->lock, flags);
-	}
+	if (!uptodate)
+		set_bit(BITMAP_WRITE_ERROR, &bitmap->flags);
 	if (atomic_dec_and_test(&bitmap->pending_writes))
 		wake_up(&bitmap->write_wait);
 }
@@ -325,8 +312,12 @@ __clear_page_buffers(struct page *page)
 }
 static void free_buffers(struct page *page)
 {
-	struct buffer_head *bh = page_buffers(page);
+	struct buffer_head *bh;
 
+	if (!PagePrivate(page))
+		return;
+
+	bh = page_buffers(page);
 	while (bh) {
 		struct buffer_head *next = bh->b_this_page;
 		free_buffer_head(bh);
@@ -343,11 +334,12 @@ static void free_buffers(struct page *page)
  * This usage is similar to how swap files are handled, and allows us
  * to write to a file with no concerns of memory allocation failing.
  */
-static struct page *read_page(struct file *file, unsigned long index,
-			      struct bitmap *bitmap,
-			      unsigned long count)
+static int read_page(struct file *file, unsigned long index,
+		     struct bitmap *bitmap,
+		     unsigned long count,
+		     struct page *page)
 {
-	struct page *page = NULL;
+	int ret = 0;
 	struct inode *inode = file->f_path.dentry->d_inode;
 	struct buffer_head *bh;
 	sector_t block;
@@ -355,16 +347,9 @@ static struct page *read_page(struct file *file, unsigned long index,
 	pr_debug("read bitmap file (%dB @ %llu)\n", (int)PAGE_SIZE,
 		 (unsigned long long)index << PAGE_SHIFT);
 
-	page = alloc_page(GFP_KERNEL);
-	if (!page)
-		page = ERR_PTR(-ENOMEM);
-	if (IS_ERR(page))
-		goto out;
-
 	bh = alloc_page_buffers(page, 1<<inode->i_blkbits, 0);
 	if (!bh) {
-		put_page(page);
-		page = ERR_PTR(-ENOMEM);
+		ret = -ENOMEM;
 		goto out;
 	}
 	attach_page_buffers(page, bh);
@@ -376,8 +361,7 @@ static struct page *read_page(struct file *file, unsigned long index,
 			bh->b_blocknr = bmap(inode, block);
 			if (bh->b_blocknr == 0) {
 				/* Cannot use this file! */
-				free_buffers(page);
-				page = ERR_PTR(-EINVAL);
+				ret = -EINVAL;
 				goto out;
 			}
 			bh->b_bdev = inode->i_sb->s_bdev;
@@ -400,17 +384,15 @@ static struct page *read_page(struct file *file, unsigned long index,
 
 	wait_event(bitmap->write_wait,
 		   atomic_read(&bitmap->pending_writes)==0);
-	if (bitmap->flags & BITMAP_WRITE_ERROR) {
-		free_buffers(page);
-		page = ERR_PTR(-EIO);
-	}
+	if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
+		ret = -EIO;
 out:
-	if (IS_ERR(page))
-		printk(KERN_ALERT "md: bitmap read error: (%dB @ %llu): %ld\n",
+	if (ret)
+		printk(KERN_ALERT "md: bitmap read error: (%dB @ %llu): %d\n",
 			(int)PAGE_SIZE,
 			(unsigned long long)index << PAGE_SHIFT,
-			PTR_ERR(page));
-	return page;
+			ret);
+	return ret;
 }
 
 /*
@@ -426,9 +408,9 @@ void bitmap_update_sb(struct bitmap *bitmap)
 		return;
 	if (bitmap->mddev->bitmap_info.external)
 		return;
-	if (!bitmap->sb_page) /* no superblock */
+	if (!bitmap->storage.sb_page) /* no superblock */
 		return;
-	sb = kmap_atomic(bitmap->sb_page);
+	sb = kmap_atomic(bitmap->storage.sb_page);
 	sb->events = cpu_to_le64(bitmap->mddev->events);
 	if (bitmap->mddev->events < bitmap->events_cleared)
 		/* rocking back to read-only */
@@ -438,8 +420,13 @@ void bitmap_update_sb(struct bitmap *bitmap)
 	/* Just in case these have been changed via sysfs: */
 	sb->daemon_sleep = cpu_to_le32(bitmap->mddev->bitmap_info.daemon_sleep/HZ);
 	sb->write_behind = cpu_to_le32(bitmap->mddev->bitmap_info.max_write_behind);
+	/* This might have been changed by a reshape */
+	sb->sync_size = cpu_to_le64(bitmap->mddev->resync_max_sectors);
+	sb->chunksize = cpu_to_le32(bitmap->mddev->bitmap_info.chunksize);
+	sb->sectors_reserved = cpu_to_le32(bitmap->mddev->
+					   bitmap_info.space);
 	kunmap_atomic(sb);
-	write_page(bitmap, bitmap->sb_page, 1);
+	write_page(bitmap, bitmap->storage.sb_page, 1);
 }
 
 /* print out the bitmap file superblock */
@@ -447,9 +434,9 @@ void bitmap_print_sb(struct bitmap *bitmap)
 {
 	bitmap_super_t *sb;
 
-	if (!bitmap || !bitmap->sb_page)
+	if (!bitmap || !bitmap->storage.sb_page)
 		return;
-	sb = kmap_atomic(bitmap->sb_page);
+	sb = kmap_atomic(bitmap->storage.sb_page);
 	printk(KERN_DEBUG "%s: bitmap file superblock:\n", bmname(bitmap));
 	printk(KERN_DEBUG "         magic: %08x\n", le32_to_cpu(sb->magic));
 	printk(KERN_DEBUG "       version: %d\n", le32_to_cpu(sb->version));
@@ -488,15 +475,15 @@ static int bitmap_new_disk_sb(struct bitmap *bitmap)
 	unsigned long chunksize, daemon_sleep, write_behind;
 	int err = -EINVAL;
 
-	bitmap->sb_page = alloc_page(GFP_KERNEL);
-	if (IS_ERR(bitmap->sb_page)) {
-		err = PTR_ERR(bitmap->sb_page);
-		bitmap->sb_page = NULL;
+	bitmap->storage.sb_page = alloc_page(GFP_KERNEL);
+	if (IS_ERR(bitmap->storage.sb_page)) {
+		err = PTR_ERR(bitmap->storage.sb_page);
+		bitmap->storage.sb_page = NULL;
 		return err;
 	}
-	bitmap->sb_page->index = 0;
+	bitmap->storage.sb_page->index = 0;
 
-	sb = kmap_atomic(bitmap->sb_page);
+	sb = kmap_atomic(bitmap->storage.sb_page);
 
 	sb->magic = cpu_to_le32(BITMAP_MAGIC);
 	sb->version = cpu_to_le32(BITMAP_MAJOR_HI);
@@ -534,8 +521,8 @@ static int bitmap_new_disk_sb(struct bitmap *bitmap)
 
 	memcpy(sb->uuid, bitmap->mddev->uuid, 16);
 
-	bitmap->flags |= BITMAP_STALE;
-	sb->state |= cpu_to_le32(BITMAP_STALE);
+	set_bit(BITMAP_STALE, &bitmap->flags);
+	sb->state = cpu_to_le32(bitmap->flags);
 	bitmap->events_cleared = bitmap->mddev->events;
 	sb->events_cleared = cpu_to_le64(bitmap->mddev->events);
 
@@ -551,31 +538,45 @@ static int bitmap_read_sb(struct bitmap *bitmap)
 	bitmap_super_t *sb;
 	unsigned long chunksize, daemon_sleep, write_behind;
 	unsigned long long events;
+	unsigned long sectors_reserved = 0;
 	int err = -EINVAL;
+	struct page *sb_page;
 
+	if (!bitmap->storage.file && !bitmap->mddev->bitmap_info.offset) {
+		chunksize = 128 * 1024 * 1024;
+		daemon_sleep = 5 * HZ;
+		write_behind = 0;
+		set_bit(BITMAP_STALE, &bitmap->flags);
+		err = 0;
+		goto out_no_sb;
+	}
 	/* page 0 is the superblock, read it... */
-	if (bitmap->file) {
-		loff_t isize = i_size_read(bitmap->file->f_mapping->host);
+	sb_page = alloc_page(GFP_KERNEL);
+	if (!sb_page)
+		return -ENOMEM;
+	bitmap->storage.sb_page = sb_page;
+
+	if (bitmap->storage.file) {
+		loff_t isize = i_size_read(bitmap->storage.file->f_mapping->host);
 		int bytes = isize > PAGE_SIZE ? PAGE_SIZE : isize;
 
-		bitmap->sb_page = read_page(bitmap->file, 0, bitmap, bytes);
+		err = read_page(bitmap->storage.file, 0,
+				bitmap, bytes, sb_page);
 	} else {
-		bitmap->sb_page = read_sb_page(bitmap->mddev,
-					       bitmap->mddev->bitmap_info.offset,
-					       NULL,
-					       0, sizeof(bitmap_super_t));
+		err = read_sb_page(bitmap->mddev,
+				   bitmap->mddev->bitmap_info.offset,
+				   sb_page,
+				   0, sizeof(bitmap_super_t));
 	}
-	if (IS_ERR(bitmap->sb_page)) {
-		err = PTR_ERR(bitmap->sb_page);
-		bitmap->sb_page = NULL;
+	if (err)
 		return err;
-	}
 
-	sb = kmap_atomic(bitmap->sb_page);
+	sb = kmap_atomic(sb_page);
 
 	chunksize = le32_to_cpu(sb->chunksize);
 	daemon_sleep = le32_to_cpu(sb->daemon_sleep) * HZ;
 	write_behind = le32_to_cpu(sb->write_behind);
+	sectors_reserved = le32_to_cpu(sb->sectors_reserved);
 
 	/* verify that the bitmap-specific fields are valid */
 	if (sb->magic != cpu_to_le32(BITMAP_MAGIC))
@@ -618,60 +619,32 @@ static int bitmap_read_sb(struct bitmap *bitmap)
 			       "-- forcing full recovery\n",
 			       bmname(bitmap), events,
 			       (unsigned long long) bitmap->mddev->events);
-			sb->state |= cpu_to_le32(BITMAP_STALE);
+			set_bit(BITMAP_STALE, &bitmap->flags);
 		}
 	}
 
 	/* assign fields using values from superblock */
-	bitmap->mddev->bitmap_info.chunksize = chunksize;
-	bitmap->mddev->bitmap_info.daemon_sleep = daemon_sleep;
-	bitmap->mddev->bitmap_info.max_write_behind = write_behind;
 	bitmap->flags |= le32_to_cpu(sb->state);
 	if (le32_to_cpu(sb->version) == BITMAP_MAJOR_HOSTENDIAN)
-		bitmap->flags |= BITMAP_HOSTENDIAN;
+		set_bit(BITMAP_HOSTENDIAN, &bitmap->flags);
 	bitmap->events_cleared = le64_to_cpu(sb->events_cleared);
-	if (bitmap->flags & BITMAP_STALE)
-		bitmap->events_cleared = bitmap->mddev->events;
 	err = 0;
 out:
 	kunmap_atomic(sb);
+out_no_sb:
+	if (test_bit(BITMAP_STALE, &bitmap->flags))
+		bitmap->events_cleared = bitmap->mddev->events;
+	bitmap->mddev->bitmap_info.chunksize = chunksize;
+	bitmap->mddev->bitmap_info.daemon_sleep = daemon_sleep;
+	bitmap->mddev->bitmap_info.max_write_behind = write_behind;
+	if (bitmap->mddev->bitmap_info.space == 0 ||
+	    bitmap->mddev->bitmap_info.space > sectors_reserved)
+		bitmap->mddev->bitmap_info.space = sectors_reserved;
 	if (err)
 		bitmap_print_sb(bitmap);
 	return err;
 }
 
-enum bitmap_mask_op {
-	MASK_SET,
-	MASK_UNSET
-};
-
-/* record the state of the bitmap in the superblock.  Return the old value */
-static int bitmap_mask_state(struct bitmap *bitmap, enum bitmap_state bits,
-			     enum bitmap_mask_op op)
-{
-	bitmap_super_t *sb;
-	int old;
-
-	if (!bitmap->sb_page) /* can't set the state */
-		return 0;
-	sb = kmap_atomic(bitmap->sb_page);
-	old = le32_to_cpu(sb->state) & bits;
-	switch (op) {
-	case MASK_SET:
-		sb->state |= cpu_to_le32(bits);
-		bitmap->flags |= bits;
-		break;
-	case MASK_UNSET:
-		sb->state &= cpu_to_le32(~bits);
-		bitmap->flags &= ~bits;
-		break;
-	default:
-		BUG();
-	}
-	kunmap_atomic(sb);
-	return old;
-}
-
 /*
  * general bitmap file operations
  */
@@ -683,17 +656,19 @@ static int bitmap_mask_state(struct bitmap *bitmap, enum bitmap_state bits,
  * file a page at a time. There's a superblock at the start of the file.
  */
 /* calculate the index of the page that contains this bit */
-static inline unsigned long file_page_index(struct bitmap *bitmap, unsigned long chunk)
+static inline unsigned long file_page_index(struct bitmap_storage *store,
+					    unsigned long chunk)
 {
-	if (!bitmap->mddev->bitmap_info.external)
+	if (store->sb_page)
 		chunk += sizeof(bitmap_super_t) << 3;
 	return chunk >> PAGE_BIT_SHIFT;
 }
 
 /* calculate the (bit) offset of this bit within a page */
-static inline unsigned long file_page_offset(struct bitmap *bitmap, unsigned long chunk)
+static inline unsigned long file_page_offset(struct bitmap_storage *store,
+					     unsigned long chunk)
 {
-	if (!bitmap->mddev->bitmap_info.external)
+	if (store->sb_page)
 		chunk += sizeof(bitmap_super_t) << 3;
 	return chunk & (PAGE_BITS - 1);
 }
@@ -705,57 +680,86 @@ static inline unsigned long file_page_offset(struct bitmap *bitmap, unsigned lon
  * 1 page (e.g., x86) or less than 1 page -- so the bitmap might start on page
  * 0 or page 1
  */
-static inline struct page *filemap_get_page(struct bitmap *bitmap,
+static inline struct page *filemap_get_page(struct bitmap_storage *store,
 					    unsigned long chunk)
 {
-	if (file_page_index(bitmap, chunk) >= bitmap->file_pages)
+	if (file_page_index(store, chunk) >= store->file_pages)
 		return NULL;
-	return bitmap->filemap[file_page_index(bitmap, chunk)
-			       - file_page_index(bitmap, 0)];
+	return store->filemap[file_page_index(store, chunk)
+			      - file_page_index(store, 0)];
 }
 
-static void bitmap_file_unmap(struct bitmap *bitmap)
+static int bitmap_storage_alloc(struct bitmap_storage *store,
+				unsigned long chunks, int with_super)
+{
+	int pnum;
+	unsigned long num_pages;
+	unsigned long bytes;
+
+	bytes = DIV_ROUND_UP(chunks, 8);
+	if (with_super)
+		bytes += sizeof(bitmap_super_t);
+
+	num_pages = DIV_ROUND_UP(bytes, PAGE_SIZE);
+
+	store->filemap = kmalloc(sizeof(struct page *)
+				 * num_pages, GFP_KERNEL);
+	if (!store->filemap)
+		return -ENOMEM;
+
+	if (with_super && !store->sb_page) {
+		store->sb_page = alloc_page(GFP_KERNEL|__GFP_ZERO);
+		if (store->sb_page == NULL)
+			return -ENOMEM;
+		store->sb_page->index = 0;
+	}
+	pnum = 0;
+	if (store->sb_page) {
+		store->filemap[0] = store->sb_page;
+		pnum = 1;
+	}
+	for ( ; pnum < num_pages; pnum++) {
+		store->filemap[pnum] = alloc_page(GFP_KERNEL|__GFP_ZERO);
+		if (!store->filemap[pnum]) {
+			store->file_pages = pnum;
+			return -ENOMEM;
+		}
+		store->filemap[pnum]->index = pnum;
+	}
+	store->file_pages = pnum;
+
+	/* We need 4 bits per page, rounded up to a multiple
+	 * of sizeof(unsigned long) */
+	store->filemap_attr = kzalloc(
+		roundup(DIV_ROUND_UP(num_pages*4, 8), sizeof(unsigned long)),
+		GFP_KERNEL);
+	if (!store->filemap_attr)
+		return -ENOMEM;
+
+	store->bytes = bytes;
+
+	return 0;
+}
+
+static void bitmap_file_unmap(struct bitmap_storage *store)
 {
 	struct page **map, *sb_page;
-	unsigned long *attr;
 	int pages;
-	unsigned long flags;
+	struct file *file;
 
-	spin_lock_irqsave(&bitmap->lock, flags);
-	map = bitmap->filemap;
-	bitmap->filemap = NULL;
-	attr = bitmap->filemap_attr;
-	bitmap->filemap_attr = NULL;
-	pages = bitmap->file_pages;
-	bitmap->file_pages = 0;
-	sb_page = bitmap->sb_page;
-	bitmap->sb_page = NULL;
-	spin_unlock_irqrestore(&bitmap->lock, flags);
+	file = store->file;
+	map = store->filemap;
+	pages = store->file_pages;
+	sb_page = store->sb_page;
 
 	while (pages--)
 		if (map[pages] != sb_page) /* 0 is sb_page, release it below */
 			free_buffers(map[pages]);
 	kfree(map);
-	kfree(attr);
+	kfree(store->filemap_attr);
 
 	if (sb_page)
 		free_buffers(sb_page);
-}
-
-static void bitmap_file_put(struct bitmap *bitmap)
-{
-	struct file *file;
-	unsigned long flags;
-
-	spin_lock_irqsave(&bitmap->lock, flags);
-	file = bitmap->file;
-	bitmap->file = NULL;
-	spin_unlock_irqrestore(&bitmap->lock, flags);
-
-	if (file)
-		wait_event(bitmap->write_wait,
-			   atomic_read(&bitmap->pending_writes)==0);
-	bitmap_file_unmap(bitmap);
 
 	if (file) {
 		struct inode *inode = file->f_path.dentry->d_inode;
@@ -773,14 +777,14 @@ static void bitmap_file_kick(struct bitmap *bitmap)
 {
 	char *path, *ptr = NULL;
 
-	if (bitmap_mask_state(bitmap, BITMAP_STALE, MASK_SET) == 0) {
+	if (!test_and_set_bit(BITMAP_STALE, &bitmap->flags)) {
 		bitmap_update_sb(bitmap);
 
-		if (bitmap->file) {
+		if (bitmap->storage.file) {
 			path = kmalloc(PAGE_SIZE, GFP_KERNEL);
 			if (path)
-				ptr = d_path(&bitmap->file->f_path, path,
-					     PAGE_SIZE);
+				ptr = d_path(&bitmap->storage.file->f_path,
+					     path, PAGE_SIZE);
 
 			printk(KERN_ALERT
 			      "%s: kicking failed bitmap file %s from array!\n",
@@ -792,10 +796,6 @@ static void bitmap_file_kick(struct bitmap *bitmap)
 			       "%s: disabling internal bitmap due to errors\n",
 			       bmname(bitmap));
 	}
-
-	bitmap_file_put(bitmap);
-
-	return;
 }
 
 enum bitmap_page_attr {
@@ -805,24 +805,30 @@ enum bitmap_page_attr {
 	BITMAP_PAGE_NEEDWRITE = 2, /* there are cleared bits that need to be synced */
 };
 
-static inline void set_page_attr(struct bitmap *bitmap, struct page *page,
-				enum bitmap_page_attr attr)
+static inline void set_page_attr(struct bitmap *bitmap, int pnum,
+				 enum bitmap_page_attr attr)
 {
-	__set_bit((page->index<<2) + attr, bitmap->filemap_attr);
+	set_bit((pnum<<2) + attr, bitmap->storage.filemap_attr);
 }
 
-static inline void clear_page_attr(struct bitmap *bitmap, struct page *page,
-				enum bitmap_page_attr attr)
+static inline void clear_page_attr(struct bitmap *bitmap, int pnum,
+				   enum bitmap_page_attr attr)
 {
-	__clear_bit((page->index<<2) + attr, bitmap->filemap_attr);
+	clear_bit((pnum<<2) + attr, bitmap->storage.filemap_attr);
 }
 
-static inline unsigned long test_page_attr(struct bitmap *bitmap, struct page *page,
-					   enum bitmap_page_attr attr)
+static inline int test_page_attr(struct bitmap *bitmap, int pnum,
+				 enum bitmap_page_attr attr)
 {
-	return test_bit((page->index<<2) + attr, bitmap->filemap_attr);
+	return test_bit((pnum<<2) + attr, bitmap->storage.filemap_attr);
 }
 
+static inline int test_and_clear_page_attr(struct bitmap *bitmap, int pnum,
+					   enum bitmap_page_attr attr)
+{
+	return test_and_clear_bit((pnum<<2) + attr,
+				  bitmap->storage.filemap_attr);
+}
 /*
  * bitmap_file_set_bit -- called before performing a write to the md device
  * to set (and eventually sync) a particular bit in the bitmap file
@@ -835,26 +841,46 @@ static void bitmap_file_set_bit(struct bitmap *bitmap, sector_t block)
 	unsigned long bit;
 	struct page *page;
 	void *kaddr;
-	unsigned long chunk = block >> bitmap->chunkshift;
+	unsigned long chunk = block >> bitmap->counts.chunkshift;
 
-	if (!bitmap->filemap)
-		return;
-
-	page = filemap_get_page(bitmap, chunk);
+	page = filemap_get_page(&bitmap->storage, chunk);
 	if (!page)
 		return;
-	bit = file_page_offset(bitmap, chunk);
+	bit = file_page_offset(&bitmap->storage, chunk);
 
 	/* set the bit */
 	kaddr = kmap_atomic(page);
-	if (bitmap->flags & BITMAP_HOSTENDIAN)
+	if (test_bit(BITMAP_HOSTENDIAN, &bitmap->flags))
 		set_bit(bit, kaddr);
 	else
-		__set_bit_le(bit, kaddr);
+		test_and_set_bit_le(bit, kaddr);
 	kunmap_atomic(kaddr);
 	pr_debug("set file bit %lu page %lu\n", bit, page->index);
 	/* record page number so it gets flushed to disk when unplug occurs */
-	set_page_attr(bitmap, page, BITMAP_PAGE_DIRTY);
+	set_page_attr(bitmap, page->index, BITMAP_PAGE_DIRTY);
+}
+
+static void bitmap_file_clear_bit(struct bitmap *bitmap, sector_t block)
+{
+	unsigned long bit;
+	struct page *page;
+	void *paddr;
+	unsigned long chunk = block >> bitmap->counts.chunkshift;
+
+	page = filemap_get_page(&bitmap->storage, chunk);
+	if (!page)
+		return;
+	bit = file_page_offset(&bitmap->storage, chunk);
+	paddr = kmap_atomic(page);
+	if (test_bit(BITMAP_HOSTENDIAN, &bitmap->flags))
+		clear_bit(bit, paddr);
+	else
+		test_and_clear_bit_le(bit, paddr);
+	kunmap_atomic(paddr);
+	if (!test_page_attr(bitmap, page->index, BITMAP_PAGE_NEEDWRITE)) {
+		set_page_attr(bitmap, page->index, BITMAP_PAGE_PENDING);
+		bitmap->allclean = 0;
+	}
 }
 
 /* this gets called when the md device is ready to unplug its underlying
@@ -862,42 +888,37 @@ static void bitmap_file_set_bit(struct bitmap *bitmap, sector_t block)
  * sync the dirty pages of the bitmap file to disk */
 void bitmap_unplug(struct bitmap *bitmap)
 {
-	unsigned long i, flags;
+	unsigned long i;
 	int dirty, need_write;
-	struct page *page;
 	int wait = 0;
 
-	if (!bitmap)
+	if (!bitmap || !bitmap->storage.filemap ||
+	    test_bit(BITMAP_STALE, &bitmap->flags))
 		return;
 
 	/* look at each page to see if there are any set bits that need to be
 	 * flushed out to disk */
-	for (i = 0; i < bitmap->file_pages; i++) {
-		spin_lock_irqsave(&bitmap->lock, flags);
-		if (!bitmap->filemap) {
-			spin_unlock_irqrestore(&bitmap->lock, flags);
+	for (i = 0; i < bitmap->storage.file_pages; i++) {
+		if (!bitmap->storage.filemap)
 			return;
+		dirty = test_and_clear_page_attr(bitmap, i, BITMAP_PAGE_DIRTY);
+		need_write = test_and_clear_page_attr(bitmap, i,
+						      BITMAP_PAGE_NEEDWRITE);
+		if (dirty || need_write) {
+			clear_page_attr(bitmap, i, BITMAP_PAGE_PENDING);
+			write_page(bitmap, bitmap->storage.filemap[i], 0);
 		}
-		page = bitmap->filemap[i];
-		dirty = test_page_attr(bitmap, page, BITMAP_PAGE_DIRTY);
-		need_write = test_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);
-		clear_page_attr(bitmap, page, BITMAP_PAGE_DIRTY);
-		clear_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);
 		if (dirty)
 			wait = 1;
-		spin_unlock_irqrestore(&bitmap->lock, flags);
-
-		if (dirty || need_write)
-			write_page(bitmap, page, 0);
 	}
 	if (wait) { /* if any writes were performed, we need to wait on them */
-		if (bitmap->file)
+		if (bitmap->storage.file)
 			wait_event(bitmap->write_wait,
 				   atomic_read(&bitmap->pending_writes)==0);
 		else
 			md_super_wait(bitmap->mddev);
 	}
-	if (bitmap->flags & BITMAP_WRITE_ERROR)
+	if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
 		bitmap_file_kick(bitmap);
 }
 EXPORT_SYMBOL(bitmap_unplug);
@@ -917,98 +938,77 @@ static void bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset, int n
 static int bitmap_init_from_disk(struct bitmap *bitmap, sector_t start)
 {
 	unsigned long i, chunks, index, oldindex, bit;
-	struct page *page = NULL, *oldpage = NULL;
-	unsigned long num_pages, bit_cnt = 0;
+	struct page *page = NULL;
+	unsigned long bit_cnt = 0;
 	struct file *file;
-	unsigned long bytes, offset;
+	unsigned long offset;
 	int outofdate;
 	int ret = -ENOSPC;
 	void *paddr;
+	struct bitmap_storage *store = &bitmap->storage;
 
-	chunks = bitmap->chunks;
-	file = bitmap->file;
+	chunks = bitmap->counts.chunks;
+	file = store->file;
 
-	BUG_ON(!file && !bitmap->mddev->bitmap_info.offset);
+	if (!file && !bitmap->mddev->bitmap_info.offset) {
+		/* No permanent bitmap - fill with '1s'. */
+		store->filemap = NULL;
+		store->file_pages = 0;
+		for (i = 0; i < chunks ; i++) {
+			/* if the disk bit is set, set the memory bit */
+			int needed = ((sector_t)(i+1) << (bitmap->counts.chunkshift)
+				      >= start);
+			bitmap_set_memory_bits(bitmap,
+					       (sector_t)i << bitmap->counts.chunkshift,
+					       needed);
+		}
+		return 0;
+	}
 
-	outofdate = bitmap->flags & BITMAP_STALE;
+	outofdate = test_bit(BITMAP_STALE, &bitmap->flags);
 	if (outofdate)
 		printk(KERN_INFO "%s: bitmap file is out of date, doing full "
 			"recovery\n", bmname(bitmap));
 
-	bytes = DIV_ROUND_UP(bitmap->chunks, 8);
-	if (!bitmap->mddev->bitmap_info.external)
-		bytes += sizeof(bitmap_super_t);
-
-	num_pages = DIV_ROUND_UP(bytes, PAGE_SIZE);
-
-	if (file && i_size_read(file->f_mapping->host) < bytes) {
+	if (file && i_size_read(file->f_mapping->host) < store->bytes) {
 		printk(KERN_INFO "%s: bitmap file too short %lu < %lu\n",
-			bmname(bitmap),
-			(unsigned long) i_size_read(file->f_mapping->host),
-			bytes);
+		       bmname(bitmap),
+		       (unsigned long) i_size_read(file->f_mapping->host),
+		       store->bytes);
 		goto err;
 	}
 
-	ret = -ENOMEM;
-
-	bitmap->filemap = kmalloc(sizeof(struct page *) * num_pages, GFP_KERNEL);
-	if (!bitmap->filemap)
-		goto err;
-
-	/* We need 4 bits per page, rounded up to a multiple of sizeof(unsigned long) */
-	bitmap->filemap_attr = kzalloc(
-		roundup(DIV_ROUND_UP(num_pages*4, 8), sizeof(unsigned long)),
-		GFP_KERNEL);
-	if (!bitmap->filemap_attr)
-		goto err;
-
 	oldindex = ~0L;
+	offset = 0;
+	if (!bitmap->mddev->bitmap_info.external)
+		offset = sizeof(bitmap_super_t);
 
 	for (i = 0; i < chunks; i++) {
 		int b;
-		index = file_page_index(bitmap, i);
-		bit = file_page_offset(bitmap, i);
+		index = file_page_index(&bitmap->storage, i);
+		bit = file_page_offset(&bitmap->storage, i);
 		if (index != oldindex) { /* this is a new page, read it in */
 			int count;
 			/* unmap the old page, we're done with it */
-			if (index == num_pages-1)
-				count = bytes - index * PAGE_SIZE;
+			if (index == store->file_pages-1)
+				count = store->bytes - index * PAGE_SIZE;
 			else
 				count = PAGE_SIZE;
-			if (index == 0 && bitmap->sb_page) {
-				/*
-				 * if we're here then the superblock page
-				 * contains some bits (PAGE_SIZE != sizeof sb)
-				 * we've already read it in, so just use it
-				 */
-				page = bitmap->sb_page;
-				offset = sizeof(bitmap_super_t);
-				if (!file)
-					page = read_sb_page(
-						bitmap->mddev,
-						bitmap->mddev->bitmap_info.offset,
-						page,
-						index, count);
-			} else if (file) {
-				page = read_page(file, index, bitmap, count);
-				offset = 0;
-			} else {
-				page = read_sb_page(bitmap->mddev,
-						    bitmap->mddev->bitmap_info.offset,
-						    NULL,
-						    index, count);
-				offset = 0;
-			}
-			if (IS_ERR(page)) { /* read error */
-				ret = PTR_ERR(page);
+			page = store->filemap[index];
+			if (file)
+				ret = read_page(file, index, bitmap,
+						count, page);
+			else
+				ret = read_sb_page(
+					bitmap->mddev,
+					bitmap->mddev->bitmap_info.offset,
+					page,
+					index, count);
+
+			if (ret)
 				goto err;
-			}
 
 			oldindex = index;
-			oldpage = page;
-
-			bitmap->filemap[bitmap->file_pages++] = page;
-			bitmap->last_page_size = count;
 
 			if (outofdate) {
 				/*
@@ -1022,39 +1022,33 @@ static int bitmap_init_from_disk(struct bitmap *bitmap, sector_t start)
 				write_page(bitmap, page, 1);
 
 				ret = -EIO;
-				if (bitmap->flags & BITMAP_WRITE_ERROR)
+				if (test_bit(BITMAP_WRITE_ERROR,
+					     &bitmap->flags))
 					goto err;
 			}
 		}
 		paddr = kmap_atomic(page);
-		if (bitmap->flags & BITMAP_HOSTENDIAN)
+		if (test_bit(BITMAP_HOSTENDIAN, &bitmap->flags))
 			b = test_bit(bit, paddr);
 		else
 			b = test_bit_le(bit, paddr);
 		kunmap_atomic(paddr);
 		if (b) {
 			/* if the disk bit is set, set the memory bit */
-			int needed = ((sector_t)(i+1) << bitmap->chunkshift
+			int needed = ((sector_t)(i+1) << bitmap->counts.chunkshift
 				      >= start);
 			bitmap_set_memory_bits(bitmap,
-					       (sector_t)i << bitmap->chunkshift,
+					       (sector_t)i << bitmap->counts.chunkshift,
 					       needed);
 			bit_cnt++;
 		}
-	}
-
-	/* everything went OK */
-	ret = 0;
-	bitmap_mask_state(bitmap, BITMAP_STALE, MASK_UNSET);
-
-	if (bit_cnt) { /* Kick recovery if any bits were set */
-		set_bit(MD_RECOVERY_NEEDED, &bitmap->mddev->recovery);
-		md_wakeup_thread(bitmap->mddev->thread);
+		offset = 0;
 	}
 
 	printk(KERN_INFO "%s: bitmap initialized from disk: "
-	       "read %lu/%lu pages, set %lu of %lu bits\n",
-	       bmname(bitmap), bitmap->file_pages, num_pages, bit_cnt, chunks);
+	       "read %lu pages, set %lu of %lu bits\n",
+	       bmname(bitmap), store->file_pages,
+	       bit_cnt, chunks);
 
 	return 0;
 
@@ -1071,22 +1065,38 @@ void bitmap_write_all(struct bitmap *bitmap)
 	 */
 	int i;
 
-	spin_lock_irq(&bitmap->lock);
-	for (i = 0; i < bitmap->file_pages; i++)
-		set_page_attr(bitmap, bitmap->filemap[i],
+	if (!bitmap || !bitmap->storage.filemap)
+		return;
+	if (bitmap->storage.file)
+		/* Only one copy, so nothing needed */
+		return;
+
+	for (i = 0; i < bitmap->storage.file_pages; i++)
+		set_page_attr(bitmap, i,
 			      BITMAP_PAGE_NEEDWRITE);
 	bitmap->allclean = 0;
-	spin_unlock_irq(&bitmap->lock);
 }
 
-static void bitmap_count_page(struct bitmap *bitmap, sector_t offset, int inc)
+static void bitmap_count_page(struct bitmap_counts *bitmap,
+			      sector_t offset, int inc)
 {
 	sector_t chunk = offset >> bitmap->chunkshift;
 	unsigned long page = chunk >> PAGE_COUNTER_SHIFT;
 	bitmap->bp[page].count += inc;
 	bitmap_checkfree(bitmap, page);
 }
-static bitmap_counter_t *bitmap_get_counter(struct bitmap *bitmap,
+
+static void bitmap_set_pending(struct bitmap_counts *bitmap, sector_t offset)
+{
+	sector_t chunk = offset >> bitmap->chunkshift;
+	unsigned long page = chunk >> PAGE_COUNTER_SHIFT;
+	struct bitmap_page *bp = &bitmap->bp[page];
+
+	if (!bp->pending)
+		bp->pending = 1;
+}
+
+static bitmap_counter_t *bitmap_get_counter(struct bitmap_counts *bitmap,
 					    sector_t offset, sector_t *blocks,
 					    int create);
 
@@ -1099,10 +1109,9 @@ void bitmap_daemon_work(struct mddev *mddev)
 {
 	struct bitmap *bitmap;
 	unsigned long j;
-	unsigned long flags;
-	struct page *page = NULL, *lastpage = NULL;
+	unsigned long nextpage;
 	sector_t blocks;
-	void *paddr;
+	struct bitmap_counts *counts;
 
 	/* Use a mutex to guard daemon_work against
 	 * bitmap_destroy.
@@ -1124,112 +1133,90 @@ void bitmap_daemon_work(struct mddev *mddev)
 	}
 	bitmap->allclean = 1;
 
-	spin_lock_irqsave(&bitmap->lock, flags);
-	for (j = 0; j < bitmap->chunks; j++) {
+	/* Any file-page which is PENDING now needs to be written.
+	 * So set NEEDWRITE now, then after we make any last-minute changes
+	 * we will write it.
+	 */
+	for (j = 0; j < bitmap->storage.file_pages; j++)
+		if (test_and_clear_page_attr(bitmap, j,
+					     BITMAP_PAGE_PENDING))
+			set_page_attr(bitmap, j,
+				      BITMAP_PAGE_NEEDWRITE);
+
+	if (bitmap->need_sync &&
+	    mddev->bitmap_info.external == 0) {
+		/* Arrange for superblock update as well as
+		 * other changes */
+		bitmap_super_t *sb;
+		bitmap->need_sync = 0;
+		if (bitmap->storage.filemap) {
+			sb = kmap_atomic(bitmap->storage.sb_page);
+			sb->events_cleared =
+				cpu_to_le64(bitmap->events_cleared);
+			kunmap_atomic(sb);
+			set_page_attr(bitmap, 0,
+				      BITMAP_PAGE_NEEDWRITE);
+		}
+	}
+	/* Now look at the bitmap counters and if any are '2' or '1',
+	 * decrement and handle accordingly.
+	 */
+	counts = &bitmap->counts;
+	spin_lock_irq(&counts->lock);
+	nextpage = 0;
+	for (j = 0; j < counts->chunks; j++) {
 		bitmap_counter_t *bmc;
-		if (!bitmap->filemap)
-			/* error or shutdown */
-			break;
+		sector_t  block = (sector_t)j << counts->chunkshift;
 
-		page = filemap_get_page(bitmap, j);
-
-		if (page != lastpage) {
-			/* skip this page unless it's marked as needing cleaning */
-			if (!test_page_attr(bitmap, page, BITMAP_PAGE_PENDING)) {
-				int need_write = test_page_attr(bitmap, page,
-								BITMAP_PAGE_NEEDWRITE);
-				if (need_write)
-					clear_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);
-
-				spin_unlock_irqrestore(&bitmap->lock, flags);
-				if (need_write)
-					write_page(bitmap, page, 0);
-				spin_lock_irqsave(&bitmap->lock, flags);
-				j |= (PAGE_BITS - 1);
+		if (j == nextpage) {
+			nextpage += PAGE_COUNTER_RATIO;
+			if (!counts->bp[j >> PAGE_COUNTER_SHIFT].pending) {
+				j |= PAGE_COUNTER_MASK;
 				continue;
 			}
-
-			/* grab the new page, sync and release the old */
-			if (lastpage != NULL) {
-				if (test_page_attr(bitmap, lastpage,
-						   BITMAP_PAGE_NEEDWRITE)) {
-					clear_page_attr(bitmap, lastpage,
-							BITMAP_PAGE_NEEDWRITE);
-					spin_unlock_irqrestore(&bitmap->lock, flags);
-					write_page(bitmap, lastpage, 0);
-				} else {
-					set_page_attr(bitmap, lastpage,
-						      BITMAP_PAGE_NEEDWRITE);
-					bitmap->allclean = 0;
-					spin_unlock_irqrestore(&bitmap->lock, flags);
-				}
-			} else
-				spin_unlock_irqrestore(&bitmap->lock, flags);
-			lastpage = page;
-
-			/* We are possibly going to clear some bits, so make
-			 * sure that events_cleared is up-to-date.
-			 */
-			if (bitmap->need_sync &&
-			    mddev->bitmap_info.external == 0) {
-				bitmap_super_t *sb;
-				bitmap->need_sync = 0;
-				sb = kmap_atomic(bitmap->sb_page);
-				sb->events_cleared =
-					cpu_to_le64(bitmap->events_cleared);
-				kunmap_atomic(sb);
-				write_page(bitmap, bitmap->sb_page, 1);
-			}
-			spin_lock_irqsave(&bitmap->lock, flags);
-			if (!bitmap->need_sync)
-				clear_page_attr(bitmap, page, BITMAP_PAGE_PENDING);
-			else
-				bitmap->allclean = 0;
+			counts->bp[j >> PAGE_COUNTER_SHIFT].pending = 0;
 		}
-		bmc = bitmap_get_counter(bitmap,
-					 (sector_t)j << bitmap->chunkshift,
+		bmc = bitmap_get_counter(counts,
+					 block,
 					 &blocks, 0);
-		if (!bmc)
+
+		if (!bmc) {
 			j |= PAGE_COUNTER_MASK;
-		else if (*bmc) {
-			if (*bmc == 1 && !bitmap->need_sync) {
-				/* we can clear the bit */
-				*bmc = 0;
-				bitmap_count_page(bitmap,
-						  (sector_t)j << bitmap->chunkshift,
-						  -1);
-
-				/* clear the bit */
-				paddr = kmap_atomic(page);
-				if (bitmap->flags & BITMAP_HOSTENDIAN)
-					clear_bit(file_page_offset(bitmap, j),
-						  paddr);
-				else
-					__clear_bit_le(
-						file_page_offset(bitmap,
-								 j),
-						paddr);
-				kunmap_atomic(paddr);
-			} else if (*bmc <= 2) {
-				*bmc = 1; /* maybe clear the bit next time */
-				set_page_attr(bitmap, page, BITMAP_PAGE_PENDING);
-				bitmap->allclean = 0;
-			}
+			continue;
 		}
-	}
-	spin_unlock_irqrestore(&bitmap->lock, flags);
-
-	/* now sync the final page */
-	if (lastpage != NULL) {
-		spin_lock_irqsave(&bitmap->lock, flags);
-		if (test_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE)) {
-			clear_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
-			spin_unlock_irqrestore(&bitmap->lock, flags);
-			write_page(bitmap, lastpage, 0);
-		} else {
-			set_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
+		if (*bmc == 1 && !bitmap->need_sync) {
+			/* We can clear the bit */
+			*bmc = 0;
+			bitmap_count_page(counts, block, -1);
+			bitmap_file_clear_bit(bitmap, block);
+		} else if (*bmc && *bmc <= 2) {
+			*bmc = 1;
+			bitmap_set_pending(counts, block);
 			bitmap->allclean = 0;
-			spin_unlock_irqrestore(&bitmap->lock, flags);
+		}
+	}
+	spin_unlock_irq(&counts->lock);
+
+	/* Now start writeout on any page in NEEDWRITE that isn't DIRTY.
+	 * DIRTY pages need to be written by bitmap_unplug so it can wait
+	 * for them.
+	 * If we find any DIRTY page we stop there and let bitmap_unplug
+	 * handle all the rest.  This is important in the case where
+	 * the first blocking holds the superblock and it has been updated.
+	 * We mustn't write any other blocks before the superblock.
+	 */
+	for (j = 0;
+	     j < bitmap->storage.file_pages
+		     && !test_bit(BITMAP_STALE, &bitmap->flags);
+	     j++) {
+
+		if (test_page_attr(bitmap, j,
+				   BITMAP_PAGE_DIRTY))
+			/* bitmap_unplug will handle the rest */
+			break;
+		if (test_and_clear_page_attr(bitmap, j,
+					     BITMAP_PAGE_NEEDWRITE)) {
+			write_page(bitmap, bitmap->storage.filemap[j], 0);
 		}
 	}
 
@@ -1240,7 +1227,7 @@ void bitmap_daemon_work(struct mddev *mddev)
 	mutex_unlock(&mddev->bitmap_info.mutex);
 }
 
-static bitmap_counter_t *bitmap_get_counter(struct bitmap *bitmap,
+static bitmap_counter_t *bitmap_get_counter(struct bitmap_counts *bitmap,
 					    sector_t offset, sector_t *blocks,
 					    int create)
 __releases(bitmap->lock)
@@ -1302,10 +1289,10 @@ int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sect
 		sector_t blocks;
 		bitmap_counter_t *bmc;
 
-		spin_lock_irq(&bitmap->lock);
-		bmc = bitmap_get_counter(bitmap, offset, &blocks, 1);
+		spin_lock_irq(&bitmap->counts.lock);
+		bmc = bitmap_get_counter(&bitmap->counts, offset, &blocks, 1);
 		if (!bmc) {
-			spin_unlock_irq(&bitmap->lock);
+			spin_unlock_irq(&bitmap->counts.lock);
 			return 0;
 		}
 
@@ -1317,7 +1304,7 @@ int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sect
 			 */
 			prepare_to_wait(&bitmap->overflow_wait, &__wait,
 					TASK_UNINTERRUPTIBLE);
-			spin_unlock_irq(&bitmap->lock);
+			spin_unlock_irq(&bitmap->counts.lock);
 			io_schedule();
 			finish_wait(&bitmap->overflow_wait, &__wait);
 			continue;
@@ -1326,7 +1313,7 @@ int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sect
 		switch (*bmc) {
 		case 0:
 			bitmap_file_set_bit(bitmap, offset);
-			bitmap_count_page(bitmap, offset, 1);
+			bitmap_count_page(&bitmap->counts, offset, 1);
 			/* fall through */
 		case 1:
 			*bmc = 2;
@@ -1334,7 +1321,7 @@ int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sect
 
 		(*bmc)++;
 
-		spin_unlock_irq(&bitmap->lock);
+		spin_unlock_irq(&bitmap->counts.lock);
 
 		offset += blocks;
 		if (sectors > blocks)
@@ -1364,10 +1351,10 @@ void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long secto
 		unsigned long flags;
 		bitmap_counter_t *bmc;
 
-		spin_lock_irqsave(&bitmap->lock, flags);
-		bmc = bitmap_get_counter(bitmap, offset, &blocks, 0);
+		spin_lock_irqsave(&bitmap->counts.lock, flags);
+		bmc = bitmap_get_counter(&bitmap->counts, offset, &blocks, 0);
 		if (!bmc) {
-			spin_unlock_irqrestore(&bitmap->lock, flags);
+			spin_unlock_irqrestore(&bitmap->counts.lock, flags);
 			return;
 		}
 
@@ -1386,14 +1373,10 @@ void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long secto
 
 		(*bmc)--;
 		if (*bmc <= 2) {
-			set_page_attr(bitmap,
-				      filemap_get_page(
-					      bitmap,
-					      offset >> bitmap->chunkshift),
-				      BITMAP_PAGE_PENDING);
+			bitmap_set_pending(&bitmap->counts, offset);
 			bitmap->allclean = 0;
 		}
-		spin_unlock_irqrestore(&bitmap->lock, flags);
+		spin_unlock_irqrestore(&bitmap->counts.lock, flags);
 		offset += blocks;
 		if (sectors > blocks)
 			sectors -= blocks;
@@ -1412,8 +1395,8 @@ static int __bitmap_start_sync(struct bitmap *bitmap, sector_t offset, sector_t
 		*blocks = 1024;
 		return 1; /* always resync if no bitmap */
 	}
-	spin_lock_irq(&bitmap->lock);
-	bmc = bitmap_get_counter(bitmap, offset, blocks, 0);
+	spin_lock_irq(&bitmap->counts.lock);
+	bmc = bitmap_get_counter(&bitmap->counts, offset, blocks, 0);
 	rv = 0;
 	if (bmc) {
 		/* locked */
@@ -1427,7 +1410,7 @@ static int __bitmap_start_sync(struct bitmap *bitmap, sector_t offset, sector_t
 			}
 		}
 	}
-	spin_unlock_irq(&bitmap->lock);
+	spin_unlock_irq(&bitmap->counts.lock);
 	return rv;
 }
 
@@ -1464,8 +1447,8 @@ void bitmap_end_sync(struct bitmap *bitmap, sector_t offset, sector_t *blocks, i
 		*blocks = 1024;
 		return;
 	}
-	spin_lock_irqsave(&bitmap->lock, flags);
-	bmc = bitmap_get_counter(bitmap, offset, blocks, 0);
+	spin_lock_irqsave(&bitmap->counts.lock, flags);
+	bmc = bitmap_get_counter(&bitmap->counts, offset, blocks, 0);
 	if (bmc == NULL)
 		goto unlock;
 	/* locked */
@@ -1476,15 +1459,13 @@ void bitmap_end_sync(struct bitmap *bitmap, sector_t offset, sector_t *blocks, i
 			*bmc |= NEEDED_MASK;
 		else {
 			if (*bmc <= 2) {
-				set_page_attr(bitmap,
-					      filemap_get_page(bitmap, offset >> bitmap->chunkshift),
-					      BITMAP_PAGE_PENDING);
+				bitmap_set_pending(&bitmap->counts, offset);
 				bitmap->allclean = 0;
 			}
 		}
 	}
  unlock:
-	spin_unlock_irqrestore(&bitmap->lock, flags);
+	spin_unlock_irqrestore(&bitmap->counts.lock, flags);
 }
 EXPORT_SYMBOL(bitmap_end_sync);
 
@@ -1524,7 +1505,7 @@ void bitmap_cond_end_sync(struct bitmap *bitmap, sector_t sector)
 
 	bitmap->mddev->curr_resync_completed = sector;
 	set_bit(MD_CHANGE_CLEAN, &bitmap->mddev->flags);
-	sector &= ~((1ULL << bitmap->chunkshift) - 1);
+	sector &= ~((1ULL << bitmap->counts.chunkshift) - 1);
 	s = 0;
 	while (s < sector && s < bitmap->mddev->resync_max_sectors) {
 		bitmap_end_sync(bitmap, s, &blocks, 0);
@@ -1538,27 +1519,25 @@ EXPORT_SYMBOL(bitmap_cond_end_sync);
 static void bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset, int needed)
 {
 	/* For each chunk covered by any of these sectors, set the
-	 * counter to 1 and set resync_needed.  They should all
+	 * counter to 2 and possibly set resync_needed.  They should all
 	 * be 0 at this point
 	 */
 
 	sector_t secs;
 	bitmap_counter_t *bmc;
-	spin_lock_irq(&bitmap->lock);
-	bmc = bitmap_get_counter(bitmap, offset, &secs, 1);
+	spin_lock_irq(&bitmap->counts.lock);
+	bmc = bitmap_get_counter(&bitmap->counts, offset, &secs, 1);
 	if (!bmc) {
-		spin_unlock_irq(&bitmap->lock);
+		spin_unlock_irq(&bitmap->counts.lock);
 		return;
 	}
 	if (!*bmc) {
-		struct page *page;
 		*bmc = 2 | (needed ? NEEDED_MASK : 0);
-		bitmap_count_page(bitmap, offset, 1);
-		page = filemap_get_page(bitmap, offset >> bitmap->chunkshift);
-		set_page_attr(bitmap, page, BITMAP_PAGE_PENDING);
+		bitmap_count_page(&bitmap->counts, offset, 1);
+		bitmap_set_pending(&bitmap->counts, offset);
 		bitmap->allclean = 0;
 	}
-	spin_unlock_irq(&bitmap->lock);
+	spin_unlock_irq(&bitmap->counts.lock);
 }
 
 /* dirty the memory and file bits for bitmap chunks "s" to "e" */
@@ -1567,11 +1546,9 @@ void bitmap_dirty_bits(struct bitmap *bitmap, unsigned long s, unsigned long e)
 	unsigned long chunk;
 
 	for (chunk = s; chunk <= e; chunk++) {
-		sector_t sec = (sector_t)chunk << bitmap->chunkshift;
+		sector_t sec = (sector_t)chunk << bitmap->counts.chunkshift;
 		bitmap_set_memory_bits(bitmap, sec, 1);
-		spin_lock_irq(&bitmap->lock);
 		bitmap_file_set_bit(bitmap, sec);
-		spin_unlock_irq(&bitmap->lock);
 		if (sec < bitmap->mddev->recovery_cp)
 			/* We are asserting that the array is dirty,
 			 * so move the recovery_cp address back so
@@ -1616,11 +1593,15 @@ static void bitmap_free(struct bitmap *bitmap)
 	if (!bitmap) /* there was no bitmap */
 		return;
 
-	/* release the bitmap file and kill the daemon */
-	bitmap_file_put(bitmap);
+	/* Shouldn't be needed - but just in case.... */
+	wait_event(bitmap->write_wait,
+		   atomic_read(&bitmap->pending_writes) == 0);
+
+	/* release the bitmap file  */
+	bitmap_file_unmap(&bitmap->storage);
 
-	bp = bitmap->bp;
-	pages = bitmap->pages;
+	bp = bitmap->counts.bp;
+	pages = bitmap->counts.pages;
 
 	/* free all allocated memory */
 
@@ -1659,25 +1640,19 @@ int bitmap_create(struct mddev *mddev)
 {
 	struct bitmap *bitmap;
 	sector_t blocks = mddev->resync_max_sectors;
-	unsigned long chunks;
-	unsigned long pages;
 	struct file *file = mddev->bitmap_info.file;
 	int err;
 	struct sysfs_dirent *bm = NULL;
 
 	BUILD_BUG_ON(sizeof(bitmap_super_t) != 256);
 
-	if (!file
-	    && !mddev->bitmap_info.offset) /* bitmap disabled, nothing to do */
-		return 0;
-
 	BUG_ON(file && mddev->bitmap_info.offset);
 
 	bitmap = kzalloc(sizeof(*bitmap), GFP_KERNEL);
 	if (!bitmap)
 		return -ENOMEM;
 
-	spin_lock_init(&bitmap->lock);
+	spin_lock_init(&bitmap->counts.lock);
 	atomic_set(&bitmap->pending_writes, 0);
 	init_waitqueue_head(&bitmap->write_wait);
 	init_waitqueue_head(&bitmap->overflow_wait);
@@ -1693,7 +1668,7 @@ int bitmap_create(struct mddev *mddev)
 	} else
 		bitmap->sysfs_can_clear = NULL;
 
-	bitmap->file = file;
+	bitmap->storage.file = file;
 	if (file) {
 		get_file(file);
 		/* As future accesses to this file will use bmap,
@@ -1724,32 +1699,15 @@ int bitmap_create(struct mddev *mddev)
 		goto error;
 
 	bitmap->daemon_lastrun = jiffies;
-	bitmap->chunkshift = (ffz(~mddev->bitmap_info.chunksize)
-			      - BITMAP_BLOCK_SHIFT);
-
-	chunks = (blocks + (1 << bitmap->chunkshift) - 1) >>
-			bitmap->chunkshift;
-	pages = (chunks + PAGE_COUNTER_RATIO - 1) / PAGE_COUNTER_RATIO;
-
-	BUG_ON(!pages);
-
-	bitmap->chunks = chunks;
-	bitmap->pages = pages;
-	bitmap->missing_pages = pages;
-
-	bitmap->bp = kzalloc(pages * sizeof(*bitmap->bp), GFP_KERNEL);
-
-	err = -ENOMEM;
-	if (!bitmap->bp)
+	err = bitmap_resize(bitmap, blocks, mddev->bitmap_info.chunksize, 1);
+	if (err)
 		goto error;
 
 	printk(KERN_INFO "created bitmap (%lu pages) for device %s\n",
-		pages, bmname(bitmap));
+	       bitmap->counts.pages, bmname(bitmap));
 
 	mddev->bitmap = bitmap;
-
-
-	return (bitmap->flags & BITMAP_WRITE_ERROR) ? -EIO : 0;
+	return test_bit(BITMAP_WRITE_ERROR, &bitmap->flags) ? -EIO : 0;
 
  error:
 	bitmap_free(bitmap);
@@ -1790,13 +1748,17 @@ int bitmap_load(struct mddev *mddev)
 
 	if (err)
 		goto out;
+	clear_bit(BITMAP_STALE, &bitmap->flags);
+
+	/* Kick recovery in case any bits were set */
+	set_bit(MD_RECOVERY_NEEDED, &bitmap->mddev->recovery);
 
 	mddev->thread->timeout = mddev->bitmap_info.daemon_sleep;
 	md_wakeup_thread(mddev->thread);
 
 	bitmap_update_sb(bitmap);
 
-	if (bitmap->flags & BITMAP_WRITE_ERROR)
+	if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
 		err = -EIO;
 out:
 	return err;
@@ -1806,30 +1768,194 @@ EXPORT_SYMBOL_GPL(bitmap_load);
 void bitmap_status(struct seq_file *seq, struct bitmap *bitmap)
 {
 	unsigned long chunk_kb;
-	unsigned long flags;
+	struct bitmap_counts *counts;
 
 	if (!bitmap)
 		return;
 
-	spin_lock_irqsave(&bitmap->lock, flags);
+	counts = &bitmap->counts;
+
 	chunk_kb = bitmap->mddev->bitmap_info.chunksize >> 10;
 	seq_printf(seq, "bitmap: %lu/%lu pages [%luKB], "
 		   "%lu%s chunk",
-		   bitmap->pages - bitmap->missing_pages,
-		   bitmap->pages,
-		   (bitmap->pages - bitmap->missing_pages)
+		   counts->pages - counts->missing_pages,
+		   counts->pages,
+		   (counts->pages - counts->missing_pages)
 		   << (PAGE_SHIFT - 10),
 		   chunk_kb ? chunk_kb : bitmap->mddev->bitmap_info.chunksize,
 		   chunk_kb ? "KB" : "B");
-	if (bitmap->file) {
+	if (bitmap->storage.file) {
 		seq_printf(seq, ", file: ");
-		seq_path(seq, &bitmap->file->f_path, " \t\n");
+		seq_path(seq, &bitmap->storage.file->f_path, " \t\n");
 	}
 
 	seq_printf(seq, "\n");
-	spin_unlock_irqrestore(&bitmap->lock, flags);
 }
 
+int bitmap_resize(struct bitmap *bitmap, sector_t blocks,
+		  int chunksize, int init)
+{
+	/* If chunk_size is 0, choose an appropriate chunk size.
+	 * Then possibly allocate new storage space.
+	 * Then quiesce, copy bits, replace bitmap, and re-start
+	 *
+	 * This function is called both to set up the initial bitmap
+	 * and to resize the bitmap while the array is active.
+	 * If this happens as a result of the array being resized,
+	 * chunksize will be zero, and we need to choose a suitable
+	 * chunksize, otherwise we use what we are given.
+	 */
+	struct bitmap_storage store;
+	struct bitmap_counts old_counts;
+	unsigned long chunks;
+	sector_t block;
+	sector_t old_blocks, new_blocks;
+	int chunkshift;
+	int ret = 0;
+	long pages;
+	struct bitmap_page *new_bp;
+
+	if (chunksize == 0) {
+		/* If there is enough space, leave the chunk size unchanged,
+		 * else increase by factor of two until there is enough space.
+		 */
+		long bytes;
+		long space = bitmap->mddev->bitmap_info.space;
+
+		if (space == 0) {
+			/* We don't know how much space there is, so limit
+			 * to current size - in sectors.
+			 */
+			bytes = DIV_ROUND_UP(bitmap->counts.chunks, 8);
+			if (!bitmap->mddev->bitmap_info.external)
+				bytes += sizeof(bitmap_super_t);
+			space = DIV_ROUND_UP(bytes, 512);
+			bitmap->mddev->bitmap_info.space = space;
+		}
+		chunkshift = bitmap->counts.chunkshift;
+		chunkshift--;
+		do {
+			/* 'chunkshift' is shift from block size to chunk size */
+			chunkshift++;
+			chunks = DIV_ROUND_UP_SECTOR_T(blocks, 1 << chunkshift);
+			bytes = DIV_ROUND_UP(chunks, 8);
+			if (!bitmap->mddev->bitmap_info.external)
+				bytes += sizeof(bitmap_super_t);
+		} while (bytes > (space << 9));
+	} else
+		chunkshift = ffz(~chunksize) - BITMAP_BLOCK_SHIFT;
+
+	chunks = DIV_ROUND_UP_SECTOR_T(blocks, 1 << chunkshift);
+	memset(&store, 0, sizeof(store));
+	if (bitmap->mddev->bitmap_info.offset || bitmap->mddev->bitmap_info.file)
+		ret = bitmap_storage_alloc(&store, chunks,
+					   !bitmap->mddev->bitmap_info.external);
+	if (ret)
+		goto err;
+
+	pages = DIV_ROUND_UP(chunks, PAGE_COUNTER_RATIO);
+
+	new_bp = kzalloc(pages * sizeof(*new_bp), GFP_KERNEL);
+	ret = -ENOMEM;
+	if (!new_bp) {
+		bitmap_file_unmap(&store);
+		goto err;
+	}
+
+	if (!init)
+		bitmap->mddev->pers->quiesce(bitmap->mddev, 1);
+
+	store.file = bitmap->storage.file;
+	bitmap->storage.file = NULL;
+
+	if (store.sb_page && bitmap->storage.sb_page)
+		memcpy(page_address(store.sb_page),
+		       page_address(bitmap->storage.sb_page),
+		       sizeof(bitmap_super_t));
+	bitmap_file_unmap(&bitmap->storage);
+	bitmap->storage = store;
+
+	old_counts = bitmap->counts;
+	bitmap->counts.bp = new_bp;
+	bitmap->counts.pages = pages;
+	bitmap->counts.missing_pages = pages;
+	bitmap->counts.chunkshift = chunkshift;
+	bitmap->counts.chunks = chunks;
+	bitmap->mddev->bitmap_info.chunksize = 1 << (chunkshift +
+						     BITMAP_BLOCK_SHIFT);
+
+	blocks = min(old_counts.chunks << old_counts.chunkshift,
+		     chunks << chunkshift);
+
+	spin_lock_irq(&bitmap->counts.lock);
+	for (block = 0; block < blocks; ) {
+		bitmap_counter_t *bmc_old, *bmc_new;
+		int set;
+
+		bmc_old = bitmap_get_counter(&old_counts, block,
+					     &old_blocks, 0);
+		set = bmc_old && NEEDED(*bmc_old);
+
+		if (set) {
+			bmc_new = bitmap_get_counter(&bitmap->counts, block,
+						     &new_blocks, 1);
+			if (*bmc_new == 0) {
+				/* need to set on-disk bits too. */
+				sector_t end = block + new_blocks;
+				sector_t start = block >> chunkshift;
+				start <<= chunkshift;
+				while (start < end) {
+					bitmap_file_set_bit(bitmap, block);
+					start += 1 << chunkshift;
+				}
+				*bmc_new = 2;
+				bitmap_count_page(&bitmap->counts,
+						  block, 1);
+				bitmap_set_pending(&bitmap->counts,
+						   block);
+			}
+			*bmc_new |= NEEDED_MASK;
+			if (new_blocks < old_blocks)
+				old_blocks = new_blocks;
+		}
+		block += old_blocks;
+	}
+
+	if (!init) {
+		int i;
+		while (block < (chunks << chunkshift)) {
+			bitmap_counter_t *bmc;
+			bmc = bitmap_get_counter(&bitmap->counts, block,
+						 &new_blocks, 1);
+			if (bmc) {
+				/* new space.  It needs to be resynced, so
+				 * we set NEEDED_MASK.
+				 */
+				if (*bmc == 0) {
+					*bmc = NEEDED_MASK | 2;
+					bitmap_count_page(&bitmap->counts,
+							  block, 1);
+					bitmap_set_pending(&bitmap->counts,
+							   block);
+				}
+			}
+			block += new_blocks;
+		}
+		for (i = 0; i < bitmap->storage.file_pages; i++)
+			set_page_attr(bitmap, i, BITMAP_PAGE_DIRTY);
+	}
+	spin_unlock_irq(&bitmap->counts.lock);
+
+	if (!init) {
+		bitmap_unplug(bitmap);
+		bitmap->mddev->pers->quiesce(bitmap->mddev, 0);
+	}
+	ret = 0;
+err:
+	return ret;
+}
+EXPORT_SYMBOL_GPL(bitmap_resize);
+
 static ssize_t
 location_show(struct mddev *mddev, char *page)
 {
@@ -1923,6 +2049,43 @@ location_store(struct mddev *mddev, const char *buf, size_t len)
 static struct md_sysfs_entry bitmap_location =
 __ATTR(location, S_IRUGO|S_IWUSR, location_show, location_store);
 
+/* 'bitmap/space' is the space available at 'location' for the
+ * bitmap.  This allows the kernel to know when it is safe to
+ * resize the bitmap to match a resized array.
+ */
+static ssize_t
+space_show(struct mddev *mddev, char *page)
+{
+	return sprintf(page, "%lu\n", mddev->bitmap_info.space);
+}
+
+static ssize_t
+space_store(struct mddev *mddev, const char *buf, size_t len)
+{
+	unsigned long sectors;
+	int rv;
+
+	rv = kstrtoul(buf, 10, &sectors);
+	if (rv)
+		return rv;
+
+	if (sectors == 0)
+		return -EINVAL;
+
+	if (mddev->bitmap &&
+	    sectors < (mddev->bitmap->storage.bytes + 511) >> 9)
+		return -EFBIG; /* Bitmap is too big for this small space */
+
+	/* could make sure it isn't too big, but that isn't really
+	 * needed - user-space should be careful.
+	 */
+	mddev->bitmap_info.space = sectors;
+	return len;
+}
+
+static struct md_sysfs_entry bitmap_space =
+__ATTR(space, S_IRUGO|S_IWUSR, space_show, space_store);
+
 static ssize_t
 timeout_show(struct mddev *mddev, char *page)
 {
@@ -2098,6 +2261,7 @@ __ATTR(max_backlog_used, S_IRUGO | S_IWUSR,
 
 static struct attribute *md_bitmap_attrs[] = {
 	&bitmap_location.attr,
+	&bitmap_space.attr,
 	&bitmap_timeout.attr,
 	&bitmap_backlog.attr,
 	&bitmap_chunksize.attr,
diff --git a/drivers/md/bitmap.h b/drivers/md/bitmap.h
index b44b0aba2d4..df4aeb6ac6f 100644
--- a/drivers/md/bitmap.h
+++ b/drivers/md/bitmap.h
@@ -111,9 +111,9 @@ typedef __u16 bitmap_counter_t;
 
 /* use these for bitmap->flags and bitmap->sb->state bit-fields */
 enum bitmap_state {
-	BITMAP_STALE  = 0x002,  /* the bitmap file is out of date or had -EIO */
-	BITMAP_WRITE_ERROR = 0x004, /* A write error has occurred */
-	BITMAP_HOSTENDIAN = 0x8000,
+	BITMAP_STALE	   = 1,  /* the bitmap file is out of date or had -EIO */
+	BITMAP_WRITE_ERROR = 2, /* A write error has occurred */
+	BITMAP_HOSTENDIAN  =15,
 };
 
 /* the superblock at the front of the bitmap file -- little endian */
@@ -128,8 +128,10 @@ typedef struct bitmap_super_s {
 	__le32 chunksize;    /* 52  the bitmap chunk size in bytes */
 	__le32 daemon_sleep; /* 56  seconds between disk flushes */
 	__le32 write_behind; /* 60  number of outstanding write-behind writes */
+	__le32 sectors_reserved; /* 64 number of 512-byte sectors that are
+				  * reserved for the bitmap. */
 
-	__u8  pad[256 - 64]; /* set to zero */
+	__u8  pad[256 - 68]; /* set to zero */
 } bitmap_super_t;
 
 /* notes:
@@ -160,35 +162,48 @@ struct bitmap_page {
 	 */
 	unsigned int hijacked:1;
 	/*
+	 * If any counter in this page is '1' or '2' - and so could be
+	 * cleared then that page is marked as 'pending'
+	 */
+	unsigned int pending:1;
+	/*
 	 * count of dirty bits on the page
 	 */
-	unsigned int  count:31;
+	unsigned int  count:30;
 };
 
 /* the main bitmap structure - one per mddev */
 struct bitmap {
-	struct bitmap_page *bp;
-	unsigned long pages; /* total number of pages in the bitmap */
-	unsigned long missing_pages; /* number of pages not yet allocated */
 
-	struct mddev *mddev; /* the md device that the bitmap is for */
+	struct bitmap_counts {
+		spinlock_t lock;
+		struct bitmap_page *bp;
+		unsigned long pages;		/* total number of pages
+						 * in the bitmap */
+		unsigned long missing_pages;	/* number of pages
+						 * not yet allocated */
+		unsigned long chunkshift;	/* chunksize = 2^chunkshift
+						 * (for bitops) */
+		unsigned long chunks;		/* Total number of data
+						 * chunks for the array */
+	} counts;
 
-	/* bitmap chunksize -- how much data does each bit represent? */
-	unsigned long chunkshift; /* chunksize = 2^(chunkshift+9) (for bitops) */
-	unsigned long chunks; /* total number of data chunks for the array */
+	struct mddev *mddev; /* the md device that the bitmap is for */
 
 	__u64	events_cleared;
 	int need_sync;
 
-	/* bitmap spinlock */
-	spinlock_t lock;
-
-	struct file *file; /* backing disk file */
-	struct page *sb_page; /* cached copy of the bitmap file superblock */
-	struct page **filemap; /* list of cache pages for the file */
-	unsigned long *filemap_attr; /* attributes associated w/ filemap pages */
-	unsigned long file_pages; /* number of pages in the file */
-	int last_page_size; /* bytes in the last page */
+	struct bitmap_storage {
+		struct file *file;		/* backing disk file */
+		struct page *sb_page;		/* cached copy of the bitmap
+						 * file superblock */
+		struct page **filemap;		/* list of cache pages for
+						 * the file */
+		unsigned long *filemap_attr;	/* attributes associated
+						 * w/ filemap pages */
+		unsigned long file_pages;	/* number of pages in the file*/
+		unsigned long bytes;		/* total bytes in the bitmap */
+	} storage;
 
 	unsigned long flags;
 
@@ -242,6 +257,9 @@ void bitmap_cond_end_sync(struct bitmap *bitmap, sector_t sector);
 
 void bitmap_unplug(struct bitmap *bitmap);
 void bitmap_daemon_work(struct mddev *mddev);
+
+int bitmap_resize(struct bitmap *bitmap, sector_t blocks,
+		  int chunksize, int init);
 #endif
 
 #endif
diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 68965e66324..017c34d78d6 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -155,10 +155,7 @@ static void context_free(struct raid_set *rs)
 	for (i = 0; i < rs->md.raid_disks; i++) {
 		if (rs->dev[i].meta_dev)
 			dm_put_device(rs->ti, rs->dev[i].meta_dev);
-		if (rs->dev[i].rdev.sb_page)
-			put_page(rs->dev[i].rdev.sb_page);
-		rs->dev[i].rdev.sb_page = NULL;
-		rs->dev[i].rdev.sb_loaded = 0;
+		md_rdev_clear(&rs->dev[i].rdev);
 		if (rs->dev[i].data_dev)
 			dm_put_device(rs->ti, rs->dev[i].data_dev);
 	}
@@ -606,7 +603,7 @@ static int read_disk_sb(struct md_rdev *rdev, int size)
 	if (!sync_page_io(rdev, 0, size, rdev->sb_page, READ, 1)) {
 		DMERR("Failed to read superblock of device at position %d",
 		      rdev->raid_disk);
-		set_bit(Faulty, &rdev->flags);
+		md_error(rdev->mddev, rdev);
 		return -EINVAL;
 	}
 
@@ -617,16 +614,18 @@ static int read_disk_sb(struct md_rdev *rdev, int size)
 
 static void super_sync(struct mddev *mddev, struct md_rdev *rdev)
 {
-	struct md_rdev *r;
+	int i;
 	uint64_t failed_devices;
 	struct dm_raid_superblock *sb;
+	struct raid_set *rs = container_of(mddev, struct raid_set, md);
 
 	sb = page_address(rdev->sb_page);
 	failed_devices = le64_to_cpu(sb->failed_devices);
 
-	rdev_for_each(r, mddev)
-		if ((r->raid_disk >= 0) && test_bit(Faulty, &r->flags))
-			failed_devices |= (1ULL << r->raid_disk);
+	for (i = 0; i < mddev->raid_disks; i++)
+		if (!rs->dev[i].data_dev ||
+		    test_bit(Faulty, &(rs->dev[i].rdev.flags)))
+			failed_devices |= (1ULL << i);
 
 	memset(sb, 0, sizeof(*sb));
 
@@ -1252,12 +1251,13 @@ static void raid_resume(struct dm_target *ti)
 {
 	struct raid_set *rs = ti->private;
 
+	set_bit(MD_CHANGE_DEVS, &rs->md.flags);
 	if (!rs->bitmap_loaded) {
 		bitmap_load(&rs->md);
 		rs->bitmap_loaded = 1;
-	} else
-		md_wakeup_thread(rs->md.thread);
+	}
 
+	clear_bit(MD_RECOVERY_FROZEN, &rs->md.recovery);
 	mddev_resume(&rs->md);
 }
 
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 01233d855eb..1c2f9048e1a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -402,6 +402,7 @@ void mddev_resume(struct mddev *mddev)
 	wake_up(&mddev->sb_wait);
 	mddev->pers->quiesce(mddev, 0);
 
+	set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
 	md_wakeup_thread(mddev->thread);
 	md_wakeup_thread(mddev->sync_thread); /* possibly kick off a reshape */
 }
@@ -452,7 +453,7 @@ static void submit_flushes(struct work_struct *ws)
 			atomic_inc(&rdev->nr_pending);
 			atomic_inc(&rdev->nr_pending);
 			rcu_read_unlock();
-			bi = bio_alloc_mddev(GFP_KERNEL, 0, mddev);
+			bi = bio_alloc_mddev(GFP_NOIO, 0, mddev);
 			bi->bi_end_io = md_end_flush;
 			bi->bi_private = rdev;
 			bi->bi_bdev = rdev->bdev;
@@ -607,6 +608,7 @@ void mddev_init(struct mddev *mddev)
 	init_waitqueue_head(&mddev->sb_wait);
 	init_waitqueue_head(&mddev->recovery_wait);
 	mddev->reshape_position = MaxSector;
+	mddev->reshape_backwards = 0;
 	mddev->resync_min = 0;
 	mddev->resync_max = MaxSector;
 	mddev->level = LEVEL_NONE;
@@ -802,7 +804,7 @@ static int alloc_disk_sb(struct md_rdev * rdev)
 	return 0;
 }
 
-static void free_disk_sb(struct md_rdev * rdev)
+void md_rdev_clear(struct md_rdev *rdev)
 {
 	if (rdev->sb_page) {
 		put_page(rdev->sb_page);
@@ -815,8 +817,10 @@ static void free_disk_sb(struct md_rdev * rdev)
 		put_page(rdev->bb_page);
 		rdev->bb_page = NULL;
 	}
+	kfree(rdev->badblocks.page);
+	rdev->badblocks.page = NULL;
 }
-
+EXPORT_SYMBOL_GPL(md_rdev_clear);
 
 static void super_written(struct bio *bio, int error)
 {
@@ -887,6 +891,10 @@ int sync_page_io(struct md_rdev *rdev, sector_t sector, int size,
 		rdev->meta_bdev : rdev->bdev;
 	if (metadata_op)
 		bio->bi_sector = sector + rdev->sb_start;
+	else if (rdev->mddev->reshape_position != MaxSector &&
+		 (rdev->mddev->reshape_backwards ==
+		  (sector >= rdev->mddev->reshape_position)))
+		bio->bi_sector = sector + rdev->new_data_offset;
 	else
 		bio->bi_sector = sector + rdev->data_offset;
 	bio_add_page(bio, page, size, 0);
@@ -1034,12 +1042,17 @@ static unsigned int calc_sb_csum(mdp_super_t * sb)
 struct super_type  {
 	char		    *name;
 	struct module	    *owner;
-	int		    (*load_super)(struct md_rdev *rdev, struct md_rdev *refdev,
+	int		    (*load_super)(struct md_rdev *rdev,
+					  struct md_rdev *refdev,
 					  int minor_version);
-	int		    (*validate_super)(struct mddev *mddev, struct md_rdev *rdev);
-	void		    (*sync_super)(struct mddev *mddev, struct md_rdev *rdev);
+	int		    (*validate_super)(struct mddev *mddev,
+					      struct md_rdev *rdev);
+	void		    (*sync_super)(struct mddev *mddev,
+					  struct md_rdev *rdev);
 	unsigned long long  (*rdev_size_change)(struct md_rdev *rdev,
 						sector_t num_sectors);
+	int		    (*allow_new_offset)(struct md_rdev *rdev,
+						unsigned long long new_offset);
 };
 
 /*
@@ -1111,6 +1124,7 @@ static int super_90_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor
 
 	rdev->preferred_minor = sb->md_minor;
 	rdev->data_offset = 0;
+	rdev->new_data_offset = 0;
 	rdev->sb_size = MD_SB_BYTES;
 	rdev->badblocks.shift = -1;
 
@@ -1184,7 +1198,11 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
 		mddev->dev_sectors = ((sector_t)sb->size) * 2;
 		mddev->events = ev1;
 		mddev->bitmap_info.offset = 0;
+		mddev->bitmap_info.space = 0;
+		/* bitmap can use 60 K after the 4K superblocks */
 		mddev->bitmap_info.default_offset = MD_SB_BYTES >> 9;
+		mddev->bitmap_info.default_space = 64*2 - (MD_SB_BYTES >> 9);
+		mddev->reshape_backwards = 0;
 
 		if (mddev->minor_version >= 91) {
 			mddev->reshape_position = sb->reshape_position;
@@ -1192,6 +1210,8 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
 			mddev->new_level = sb->new_level;
 			mddev->new_layout = sb->new_layout;
 			mddev->new_chunk_sectors = sb->new_chunk >> 9;
+			if (mddev->delta_disks < 0)
+				mddev->reshape_backwards = 1;
 		} else {
 			mddev->reshape_position = MaxSector;
 			mddev->delta_disks = 0;
@@ -1218,9 +1238,12 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
 		mddev->max_disks = MD_SB_DISKS;
 
 		if (sb->state & (1<<MD_SB_BITMAP_PRESENT) &&
-		    mddev->bitmap_info.file == NULL)
+		    mddev->bitmap_info.file == NULL) {
 			mddev->bitmap_info.offset =
 				mddev->bitmap_info.default_offset;
+			mddev->bitmap_info.space =
+				mddev->bitmap_info.space;
+		}
 
 	} else if (mddev->pers == NULL) {
 		/* Insist on good event counter while assembling, except
@@ -1434,6 +1457,12 @@ super_90_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
 	return num_sectors;
 }
 
+static int
+super_90_allow_new_offset(struct md_rdev *rdev, unsigned long long new_offset)
+{
+	/* non-zero offset changes not possible with v0.90 */
+	return new_offset == 0;
+}
 
 /*
  * version 1 superblock
@@ -1469,6 +1498,7 @@ static int super_1_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor_
 	struct mdp_superblock_1 *sb;
 	int ret;
 	sector_t sb_start;
+	sector_t sectors;
 	char b[BDEVNAME_SIZE], b2[BDEVNAME_SIZE];
 	int bmask;
 
@@ -1523,9 +1553,18 @@ static int super_1_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor_
 		       bdevname(rdev->bdev,b));
 		return -EINVAL;
 	}
+	if (sb->pad0 ||
+	    sb->pad3[0] ||
+	    memcmp(sb->pad3, sb->pad3+1, sizeof(sb->pad3) - sizeof(sb->pad3[1])))
+		/* Some padding is non-zero, might be a new feature */
+		return -EINVAL;
 
 	rdev->preferred_minor = 0xffff;
 	rdev->data_offset = le64_to_cpu(sb->data_offset);
+	rdev->new_data_offset = rdev->data_offset;
+	if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_RESHAPE_ACTIVE) &&
+	    (le32_to_cpu(sb->feature_map) & MD_FEATURE_NEW_OFFSET))
+		rdev->new_data_offset += (s32)le32_to_cpu(sb->new_offset);
 	atomic_set(&rdev->corrected_errors, le32_to_cpu(sb->cnt_corrected_read));
 
 	rdev->sb_size = le32_to_cpu(sb->max_dev) * 2 + 256;
@@ -1536,6 +1575,9 @@ static int super_1_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor_
 	if (minor_version
 	    && rdev->data_offset < sb_start + (rdev->sb_size/512))
 		return -EINVAL;
+	if (minor_version
+	    && rdev->new_data_offset < sb_start + (rdev->sb_size/512))
+		return -EINVAL;
 
 	if (sb->level == cpu_to_le32(LEVEL_MULTIPATH))
 		rdev->desc_nr = -1;
@@ -1607,16 +1649,14 @@ static int super_1_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor_
 		else
 			ret = 0;
 	}
-	if (minor_version)
-		rdev->sectors = (i_size_read(rdev->bdev->bd_inode) >> 9) -
-			le64_to_cpu(sb->data_offset);
-	else
-		rdev->sectors = rdev->sb_start;
-	if (rdev->sectors < le64_to_cpu(sb->data_size))
+	if (minor_version) {
+		sectors = (i_size_read(rdev->bdev->bd_inode) >> 9);
+		sectors -= rdev->data_offset;
+	} else
+		sectors = rdev->sb_start;
+	if (sectors < le64_to_cpu(sb->data_size))
 		return -EINVAL;
 	rdev->sectors = le64_to_cpu(sb->data_size);
-	if (le64_to_cpu(sb->size) > rdev->sectors)
-		return -EINVAL;
 	return ret;
 }
 
@@ -1644,17 +1684,37 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
 		mddev->dev_sectors = le64_to_cpu(sb->size);
 		mddev->events = ev1;
 		mddev->bitmap_info.offset = 0;
+		mddev->bitmap_info.space = 0;
+		/* Default location for bitmap is 1K after superblock
+		 * using 3K - total of 4K
+		 */
 		mddev->bitmap_info.default_offset = 1024 >> 9;
-		
+		mddev->bitmap_info.default_space = (4096-1024) >> 9;
+		mddev->reshape_backwards = 0;
+
 		mddev->recovery_cp = le64_to_cpu(sb->resync_offset);
 		memcpy(mddev->uuid, sb->set_uuid, 16);
 
 		mddev->max_disks =  (4096-256)/2;
 
 		if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_BITMAP_OFFSET) &&
-		    mddev->bitmap_info.file == NULL )
+		    mddev->bitmap_info.file == NULL) {
 			mddev->bitmap_info.offset =
 				(__s32)le32_to_cpu(sb->bitmap_offset);
+			/* Metadata doesn't record how much space is available.
+			 * For 1.0, we assume we can use up to the superblock
+			 * if before, else to 4K beyond superblock.
+			 * For others, assume no change is possible.
+			 */
+			if (mddev->minor_version > 0)
+				mddev->bitmap_info.space = 0;
+			else if (mddev->bitmap_info.offset > 0)
+				mddev->bitmap_info.space =
+					8 - mddev->bitmap_info.offset;
+			else
+				mddev->bitmap_info.space =
+					-mddev->bitmap_info.offset;
+		}
 
 		if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_RESHAPE_ACTIVE)) {
 			mddev->reshape_position = le64_to_cpu(sb->reshape_position);
@@ -1662,6 +1722,11 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
 			mddev->new_level = le32_to_cpu(sb->new_level);
 			mddev->new_layout = le32_to_cpu(sb->new_layout);
 			mddev->new_chunk_sectors = le32_to_cpu(sb->new_chunk);
+			if (mddev->delta_disks < 0 ||
+			    (mddev->delta_disks == 0 &&
+			     (le32_to_cpu(sb->feature_map)
+			      & MD_FEATURE_RESHAPE_BACKWARDS)))
+				mddev->reshape_backwards = 1;
 		} else {
 			mddev->reshape_position = MaxSector;
 			mddev->delta_disks = 0;
@@ -1735,7 +1800,6 @@ static void super_1_sync(struct mddev *mddev, struct md_rdev *rdev)
 	sb->feature_map = 0;
 	sb->pad0 = 0;
 	sb->recovery_offset = cpu_to_le64(0);
-	memset(sb->pad1, 0, sizeof(sb->pad1));
 	memset(sb->pad3, 0, sizeof(sb->pad3));
 
 	sb->utime = cpu_to_le64((__u64)mddev->utime);
@@ -1757,6 +1821,8 @@ static void super_1_sync(struct mddev *mddev, struct md_rdev *rdev)
 		sb->devflags |= WriteMostly1;
 	else
 		sb->devflags &= ~WriteMostly1;
+	sb->data_offset = cpu_to_le64(rdev->data_offset);
+	sb->data_size = cpu_to_le64(rdev->sectors);
 
 	if (mddev->bitmap && mddev->bitmap_info.file == NULL) {
 		sb->bitmap_offset = cpu_to_le32((__u32)mddev->bitmap_info.offset);
@@ -1781,6 +1847,16 @@ static void super_1_sync(struct mddev *mddev, struct md_rdev *rdev)
 		sb->delta_disks = cpu_to_le32(mddev->delta_disks);
 		sb->new_level = cpu_to_le32(mddev->new_level);
 		sb->new_chunk = cpu_to_le32(mddev->new_chunk_sectors);
+		if (mddev->delta_disks == 0 &&
+		    mddev->reshape_backwards)
+			sb->feature_map
+				|= cpu_to_le32(MD_FEATURE_RESHAPE_BACKWARDS);
+		if (rdev->new_data_offset != rdev->data_offset) {
+			sb->feature_map
+				|= cpu_to_le32(MD_FEATURE_NEW_OFFSET);
+			sb->new_offset = cpu_to_le32((__u32)(rdev->new_data_offset
+							     - rdev->data_offset));
+		}
 	}
 
 	if (rdev->badblocks.count == 0)
@@ -1857,6 +1933,8 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
 	sector_t max_sectors;
 	if (num_sectors && num_sectors < rdev->mddev->dev_sectors)
 		return 0; /* component must fit device */
+	if (rdev->data_offset != rdev->new_data_offset)
+		return 0; /* too confusing */
 	if (rdev->sb_start < rdev->data_offset) {
 		/* minor versions 1 and 2; superblock before data */
 		max_sectors = i_size_read(rdev->bdev->bd_inode) >> 9;
@@ -1884,6 +1962,40 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
 		       rdev->sb_page);
 	md_super_wait(rdev->mddev);
 	return num_sectors;
+
+}
+
+static int
+super_1_allow_new_offset(struct md_rdev *rdev,
+			 unsigned long long new_offset)
+{
+	/* All necessary checks on new >= old have been done */
+	struct bitmap *bitmap;
+	if (new_offset >= rdev->data_offset)
+		return 1;
+
+	/* with 1.0 metadata, there is no metadata to tread on
+	 * so we can always move back */
+	if (rdev->mddev->minor_version == 0)
+		return 1;
+
+	/* otherwise we must be sure not to step on
+	 * any metadata, so stay:
+	 * 36K beyond start of superblock
+	 * beyond end of badblocks
+	 * beyond write-intent bitmap
+	 */
+	if (rdev->sb_start + (32+4)*2 > new_offset)
+		return 0;
+	bitmap = rdev->mddev->bitmap;
+	if (bitmap && !rdev->mddev->bitmap_info.file &&
+	    rdev->sb_start + rdev->mddev->bitmap_info.offset +
+	    bitmap->storage.file_pages * (PAGE_SIZE>>9) > new_offset)
+		return 0;
+	if (rdev->badblocks.sector + rdev->badblocks.size > new_offset)
+		return 0;
+
+	return 1;
 }
 
 static struct super_type super_types[] = {
@@ -1894,6 +2006,7 @@ static struct super_type super_types[] = {
 		.validate_super	    = super_90_validate,
 		.sync_super	    = super_90_sync,
 		.rdev_size_change   = super_90_rdev_size_change,
+		.allow_new_offset   = super_90_allow_new_offset,
 	},
 	[1] = {
 		.name	= "md-1",
@@ -1902,6 +2015,7 @@ static struct super_type super_types[] = {
 		.validate_super	    = super_1_validate,
 		.sync_super	    = super_1_sync,
 		.rdev_size_change   = super_1_rdev_size_change,
+		.allow_new_offset   = super_1_allow_new_offset,
 	},
 };
 
@@ -2105,9 +2219,7 @@ static void unbind_rdev_from_array(struct md_rdev * rdev)
 	sysfs_remove_link(&rdev->kobj, "block");
 	sysfs_put(rdev->sysfs_state);
 	rdev->sysfs_state = NULL;
-	kfree(rdev->badblocks.page);
 	rdev->badblocks.count = 0;
-	rdev->badblocks.page = NULL;
 	/* We need to delay this, otherwise we can deadlock when
 	 * writing to 'remove' to "dev/state".  We also need
 	 * to delay it due to rcu usage.
@@ -2158,7 +2270,7 @@ static void export_rdev(struct md_rdev * rdev)
 		bdevname(rdev->bdev,b));
 	if (rdev->mddev)
 		MD_BUG();
-	free_disk_sb(rdev);
+	md_rdev_clear(rdev);
 #ifndef MODULE
 	if (test_bit(AutoDetected, &rdev->flags))
 		md_autodetect_dev(rdev->bdev->bd_dev);
@@ -2809,9 +2921,8 @@ offset_show(struct md_rdev *rdev, char *page)
 static ssize_t
 offset_store(struct md_rdev *rdev, const char *buf, size_t len)
 {
-	char *e;
-	unsigned long long offset = simple_strtoull(buf, &e, 10);
-	if (e==buf || (*e && *e != '\n'))
+	unsigned long long offset;
+	if (strict_strtoull(buf, 10, &offset) < 0)
 		return -EINVAL;
 	if (rdev->mddev->pers && rdev->raid_disk >= 0)
 		return -EBUSY;
@@ -2826,6 +2937,63 @@ offset_store(struct md_rdev *rdev, const char *buf, size_t len)
 static struct rdev_sysfs_entry rdev_offset =
 __ATTR(offset, S_IRUGO|S_IWUSR, offset_show, offset_store);
 
+static ssize_t new_offset_show(struct md_rdev *rdev, char *page)
+{
+	return sprintf(page, "%llu\n",
+		       (unsigned long long)rdev->new_data_offset);
+}
+
+static ssize_t new_offset_store(struct md_rdev *rdev,
+				const char *buf, size_t len)
+{
+	unsigned long long new_offset;
+	struct mddev *mddev = rdev->mddev;
+
+	if (strict_strtoull(buf, 10, &new_offset) < 0)
+		return -EINVAL;
+
+	if (mddev->sync_thread)
+		return -EBUSY;
+	if (new_offset == rdev->data_offset)
+		/* reset is always permitted */
+		;
+	else if (new_offset > rdev->data_offset) {
+		/* must not push array size beyond rdev_sectors */
+		if (new_offset - rdev->data_offset
+		    + mddev->dev_sectors > rdev->sectors)
+				return -E2BIG;
+	}
+	/* Metadata worries about other space details. */
+
+	/* decreasing the offset is inconsistent with a backwards
+	 * reshape.
+	 */
+	if (new_offset < rdev->data_offset &&
+	    mddev->reshape_backwards)
+		return -EINVAL;
+	/* Increasing offset is inconsistent with forwards
+	 * reshape.  reshape_direction should be set to
+	 * 'backwards' first.
+	 */
+	if (new_offset > rdev->data_offset &&
+	    !mddev->reshape_backwards)
+		return -EINVAL;
+
+	if (mddev->pers && mddev->persistent &&
+	    !super_types[mddev->major_version]
+	    .allow_new_offset(rdev, new_offset))
+		return -E2BIG;
+	rdev->new_data_offset = new_offset;
+	if (new_offset > rdev->data_offset)
+		mddev->reshape_backwards = 1;
+	else if (new_offset < rdev->data_offset)
+		mddev->reshape_backwards = 0;
+
+	return len;
+}
+static struct rdev_sysfs_entry rdev_new_offset =
+__ATTR(new_offset, S_IRUGO|S_IWUSR, new_offset_show, new_offset_store);
+
 static ssize_t
 rdev_size_show(struct md_rdev *rdev, char *page)
 {
@@ -2870,6 +3038,8 @@ rdev_size_store(struct md_rdev *rdev, const char *buf, size_t len)
 
 	if (strict_blocks_to_sectors(buf, &sectors) < 0)
 		return -EINVAL;
+	if (rdev->data_offset != rdev->new_data_offset)
+		return -EINVAL; /* too confusing */
 	if (my_mddev->pers && rdev->raid_disk >= 0) {
 		if (my_mddev->persistent) {
 			sectors = super_types[my_mddev->major_version].
@@ -3006,6 +3176,7 @@ static struct attribute *rdev_default_attrs[] = {
 	&rdev_errors.attr,
 	&rdev_slot.attr,
 	&rdev_offset.attr,
+	&rdev_new_offset.attr,
 	&rdev_size.attr,
 	&rdev_recovery_start.attr,
 	&rdev_bad_blocks.attr,
@@ -3080,6 +3251,7 @@ int md_rdev_init(struct md_rdev *rdev)
 	rdev->raid_disk = -1;
 	rdev->flags = 0;
 	rdev->data_offset = 0;
+	rdev->new_data_offset = 0;
 	rdev->sb_events = 0;
 	rdev->last_read_error.tv_sec  = 0;
 	rdev->last_read_error.tv_nsec = 0;
@@ -3178,8 +3350,7 @@ static struct md_rdev *md_import_device(dev_t newdev, int super_format, int supe
 abort_free:
 	if (rdev->bdev)
 		unlock_rdev(rdev);
-	free_disk_sb(rdev);
-	kfree(rdev->badblocks.page);
+	md_rdev_clear(rdev);
 	kfree(rdev);
 	return ERR_PTR(err);
 }
@@ -3419,6 +3590,7 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 		mddev->new_chunk_sectors = mddev->chunk_sectors;
 		mddev->raid_disks -= mddev->delta_disks;
 		mddev->delta_disks = 0;
+		mddev->reshape_backwards = 0;
 		module_put(pers->owner);
 		printk(KERN_WARNING "md: %s: %s would not accept array\n",
 		       mdname(mddev), clevel);
@@ -3492,6 +3664,7 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 	mddev->layout = mddev->new_layout;
 	mddev->chunk_sectors = mddev->new_chunk_sectors;
 	mddev->delta_disks = 0;
+	mddev->reshape_backwards = 0;
 	mddev->degraded = 0;
 	if (mddev->pers->sync_request == NULL) {
 		/* this is now an array without redundancy, so
@@ -3501,10 +3674,8 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 		del_timer_sync(&mddev->safemode_timer);
 	}
 	pers->run(mddev);
-	mddev_resume(mddev);
 	set_bit(MD_CHANGE_DEVS, &mddev->flags);
-	set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
-	md_wakeup_thread(mddev->thread);
+	mddev_resume(mddev);
 	sysfs_notify(&mddev->kobj, NULL, "level");
 	md_new_event(mddev);
 	return rv;
@@ -3582,9 +3753,20 @@ raid_disks_store(struct mddev *mddev, const char *buf, size_t len)
 	if (mddev->pers)
 		rv = update_raid_disks(mddev, n);
 	else if (mddev->reshape_position != MaxSector) {
+		struct md_rdev *rdev;
 		int olddisks = mddev->raid_disks - mddev->delta_disks;
+
+		rdev_for_each(rdev, mddev) {
+			if (olddisks < n &&
+			    rdev->data_offset < rdev->new_data_offset)
+				return -EINVAL;
+			if (olddisks > n &&
+			    rdev->data_offset > rdev->new_data_offset)
+				return -EINVAL;
+		}
 		mddev->delta_disks = n - olddisks;
 		mddev->raid_disks = n;
+		mddev->reshape_backwards = (mddev->delta_disks < 0);
 	} else
 		mddev->raid_disks = n;
 	return rv ? rv : len;
@@ -4266,7 +4448,8 @@ sync_completed_show(struct mddev *mddev, char *page)
 	if (!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
 		return sprintf(page, "none\n");
 
-	if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
+	if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) ||
+	    test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
 		max_sectors = mddev->resync_max_sectors;
 	else
 		max_sectors = mddev->dev_sectors;
@@ -4428,6 +4611,7 @@ reshape_position_show(struct mddev *mddev, char *page)
 static ssize_t
 reshape_position_store(struct mddev *mddev, const char *buf, size_t len)
 {
+	struct md_rdev *rdev;
 	char *e;
 	unsigned long long new = simple_strtoull(buf, &e, 10);
 	if (mddev->pers)
@@ -4436,9 +4620,12 @@ reshape_position_store(struct mddev *mddev, const char *buf, size_t len)
 		return -EINVAL;
 	mddev->reshape_position = new;
 	mddev->delta_disks = 0;
+	mddev->reshape_backwards = 0;
 	mddev->new_level = mddev->level;
 	mddev->new_layout = mddev->layout;
 	mddev->new_chunk_sectors = mddev->chunk_sectors;
+	rdev_for_each(rdev, mddev)
+		rdev->new_data_offset = rdev->data_offset;
 	return len;
 }
 
@@ -4447,6 +4634,42 @@ __ATTR(reshape_position, S_IRUGO|S_IWUSR, reshape_position_show,
        reshape_position_store);
 
 static ssize_t
+reshape_direction_show(struct mddev *mddev, char *page)
+{
+	return sprintf(page, "%s\n",
+		       mddev->reshape_backwards ? "backwards" : "forwards");
+}
+
+static ssize_t
+reshape_direction_store(struct mddev *mddev, const char *buf, size_t len)
+{
+	int backwards = 0;
+	if (cmd_match(buf, "forwards"))
+		backwards = 0;
+	else if (cmd_match(buf, "backwards"))
+		backwards = 1;
+	else
+		return -EINVAL;
+	if (mddev->reshape_backwards == backwards)
+		return len;
+
+	/* check if we are allowed to change */
+	if (mddev->delta_disks)
+		return -EBUSY;
+
+	if (mddev->persistent &&
+	    mddev->major_version == 0)
+		return -EINVAL;
+
+	mddev->reshape_backwards = backwards;
+	return len;
+}
+
+static struct md_sysfs_entry md_reshape_direction =
+__ATTR(reshape_direction, S_IRUGO|S_IWUSR, reshape_direction_show,
+       reshape_direction_store);
+
+static ssize_t
 array_size_show(struct mddev *mddev, char *page)
 {
 	if (mddev->external_size)
@@ -4501,6 +4724,7 @@ static struct attribute *md_default_attrs[] = {
 	&md_safe_delay.attr,
 	&md_array_state.attr,
 	&md_reshape_position.attr,
+	&md_reshape_direction.attr,
 	&md_array_size.attr,
 	&max_corr_read_errors.attr,
 	NULL,
@@ -4914,7 +5138,8 @@ int md_run(struct mddev *mddev)
 		err = -EINVAL;
 		mddev->pers->stop(mddev);
 	}
-	if (err == 0 && mddev->pers->sync_request) {
+	if (err == 0 && mddev->pers->sync_request &&
+	    (mddev->bitmap_info.file || mddev->bitmap_info.offset)) {
 		err = bitmap_create(mddev);
 		if (err) {
 			printk(KERN_ERR "%s: failed to create bitmap (%d)\n",
@@ -5064,6 +5289,7 @@ static void md_clean(struct mddev *mddev)
 	mddev->events = 0;
 	mddev->can_decrease_events = 0;
 	mddev->delta_disks = 0;
+	mddev->reshape_backwards = 0;
 	mddev->new_level = LEVEL_NONE;
 	mddev->new_layout = 0;
 	mddev->new_chunk_sectors = 0;
@@ -5079,6 +5305,7 @@ static void md_clean(struct mddev *mddev)
 	mddev->merge_check_needed = 0;
 	mddev->bitmap_info.offset = 0;
 	mddev->bitmap_info.default_offset = 0;
+	mddev->bitmap_info.default_space = 0;
 	mddev->bitmap_info.chunksize = 0;
 	mddev->bitmap_info.daemon_sleep = 0;
 	mddev->bitmap_info.max_write_behind = 0;
@@ -5421,7 +5648,7 @@ static int get_bitmap_file(struct mddev * mddev, void __user * arg)
 		goto out;
 
 	/* bitmap disabled, zero the first byte and copy out */
-	if (!mddev->bitmap || !mddev->bitmap->file) {
+	if (!mddev->bitmap || !mddev->bitmap->storage.file) {
 		file->pathname[0] = '\0';
 		goto copy_out;
 	}
@@ -5430,7 +5657,8 @@ static int get_bitmap_file(struct mddev * mddev, void __user * arg)
 	if (!buf)
 		goto out;
 
-	ptr = d_path(&mddev->bitmap->file->f_path, buf, sizeof(file->pathname));
+	ptr = d_path(&mddev->bitmap->storage.file->f_path,
+		     buf, sizeof(file->pathname));
 	if (IS_ERR(ptr))
 		goto out;
 
@@ -5875,6 +6103,7 @@ static int set_array_info(struct mddev * mddev, mdu_array_info_t *info)
 	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 
 	mddev->bitmap_info.default_offset = MD_SB_BYTES >> 9;
+	mddev->bitmap_info.default_space = 64*2 - (MD_SB_BYTES >> 9);
 	mddev->bitmap_info.offset = 0;
 
 	mddev->reshape_position = MaxSector;
@@ -5888,6 +6117,7 @@ static int set_array_info(struct mddev * mddev, mdu_array_info_t *info)
 	mddev->new_chunk_sectors = mddev->chunk_sectors;
 	mddev->new_layout = mddev->layout;
 	mddev->delta_disks = 0;
+	mddev->reshape_backwards = 0;
 
 	return 0;
 }
@@ -5922,11 +6152,7 @@ static int update_size(struct mddev *mddev, sector_t num_sectors)
 	 */
 	if (mddev->sync_thread)
 		return -EBUSY;
-	if (mddev->bitmap)
-		/* Sorry, cannot grow a bitmap yet, just remove it,
-		 * grow, and re-add.
-		 */
-		return -EBUSY;
+
 	rdev_for_each(rdev, mddev) {
 		sector_t avail = rdev->sectors;
 
@@ -5944,6 +6170,7 @@ static int update_size(struct mddev *mddev, sector_t num_sectors)
 static int update_raid_disks(struct mddev *mddev, int raid_disks)
 {
 	int rv;
+	struct md_rdev *rdev;
 	/* change the number of raid disks */
 	if (mddev->pers->check_reshape == NULL)
 		return -EINVAL;
@@ -5952,11 +6179,27 @@ static int update_raid_disks(struct mddev *mddev, int raid_disks)
 		return -EINVAL;
 	if (mddev->sync_thread || mddev->reshape_position != MaxSector)
 		return -EBUSY;
+
+	rdev_for_each(rdev, mddev) {
+		if (mddev->raid_disks < raid_disks &&
+		    rdev->data_offset < rdev->new_data_offset)
+			return -EINVAL;
+		if (mddev->raid_disks > raid_disks &&
+		    rdev->data_offset > rdev->new_data_offset)
+			return -EINVAL;
+	}
+
 	mddev->delta_disks = raid_disks - mddev->raid_disks;
+	if (mddev->delta_disks < 0)
+		mddev->reshape_backwards = 1;
+	else if (mddev->delta_disks > 0)
+		mddev->reshape_backwards = 0;
 
 	rv = mddev->pers->check_reshape(mddev);
-	if (rv < 0)
+	if (rv < 0) {
 		mddev->delta_disks = 0;
+		mddev->reshape_backwards = 0;
+	}
 	return rv;
 }
 
@@ -6039,6 +6282,8 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 				return -EINVAL;
 			mddev->bitmap_info.offset =
 				mddev->bitmap_info.default_offset;
+			mddev->bitmap_info.space =
+				mddev->bitmap_info.default_space;
 			mddev->pers->quiesce(mddev, 1);
 			rv = bitmap_create(mddev);
 			if (!rv)
@@ -6050,7 +6295,7 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 			/* remove the bitmap */
 			if (!mddev->bitmap)
 				return -ENOENT;
-			if (mddev->bitmap->file)
+			if (mddev->bitmap->storage.file)
 				return -EINVAL;
 			mddev->pers->quiesce(mddev, 1);
 			bitmap_destroy(mddev);
@@ -6373,6 +6618,9 @@ static int md_open(struct block_device *bdev, fmode_t mode)
 	struct mddev *mddev = mddev_find(bdev->bd_dev);
 	int err;
 
+	if (!mddev)
+		return -ENODEV;
+
 	if (mddev->gendisk != bdev->bd_disk) {
 		/* we are racing with mddev_put which is discarding this
 		 * bd_disk.
@@ -6584,7 +6832,8 @@ static void status_resync(struct seq_file *seq, struct mddev * mddev)
 
 	resync = mddev->curr_resync - atomic_read(&mddev->recovery_active);
 
-	if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
+	if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) ||
+	    test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
 		max_sectors = mddev->resync_max_sectors;
 	else
 		max_sectors = mddev->dev_sectors;
@@ -7147,7 +7396,7 @@ void md_do_sync(struct mddev *mddev)
 			j = mddev->recovery_cp;
 
 	} else if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
-		max_sectors = mddev->dev_sectors;
+		max_sectors = mddev->resync_max_sectors;
 	else {
 		/* recovery follows the physical size of devices */
 		max_sectors = mddev->dev_sectors;
@@ -7598,7 +7847,7 @@ void md_check_recovery(struct mddev *mddev)
 			goto unlock;
 
 		if (mddev->pers->sync_request) {
-			if (spares && mddev->bitmap && ! mddev->bitmap->file) {
+			if (spares) {
 				/* We are adding a device or devices to an array
 				 * which has the bitmap stored on all devices.
 				 * So make sure all bitmap pages get written
@@ -7646,6 +7895,20 @@ void md_wait_for_blocked_rdev(struct md_rdev *rdev, struct mddev *mddev)
 }
 EXPORT_SYMBOL(md_wait_for_blocked_rdev);
 
+void md_finish_reshape(struct mddev *mddev)
+{
+	/* called be personality module when reshape completes. */
+	struct md_rdev *rdev;
+
+	rdev_for_each(rdev, mddev) {
+		if (rdev->data_offset > rdev->new_data_offset)
+			rdev->sectors += rdev->data_offset - rdev->new_data_offset;
+		else
+			rdev->sectors -= rdev->new_data_offset - rdev->data_offset;
+		rdev->data_offset = rdev->new_data_offset;
+	}
+}
+EXPORT_SYMBOL(md_finish_reshape);
 
 /* Bad block management.
  * We can record which blocks on each device are 'bad' and so just
@@ -7894,10 +8157,15 @@ static int md_set_badblocks(struct badblocks *bb, sector_t s, int sectors,
 }
 
 int rdev_set_badblocks(struct md_rdev *rdev, sector_t s, int sectors,
-		       int acknowledged)
+		       int is_new)
 {
-	int rv = md_set_badblocks(&rdev->badblocks,
-				  s + rdev->data_offset, sectors, acknowledged);
+	int rv;
+	if (is_new)
+		s += rdev->new_data_offset;
+	else
+		s += rdev->data_offset;
+	rv = md_set_badblocks(&rdev->badblocks,
+			      s, sectors, 0);
 	if (rv) {
 		/* Make sure they get written out promptly */
 		sysfs_notify_dirent_safe(rdev->sysfs_state);
@@ -8003,11 +8271,15 @@ out:
 	return rv;
 }
 
-int rdev_clear_badblocks(struct md_rdev *rdev, sector_t s, int sectors)
+int rdev_clear_badblocks(struct md_rdev *rdev, sector_t s, int sectors,
+			 int is_new)
 {
+	if (is_new)
+		s += rdev->new_data_offset;
+	else
+		s += rdev->data_offset;
 	return md_clear_badblocks(&rdev->badblocks,
-				  s + rdev->data_offset,
-				  sectors);
+				  s, sectors);
 }
 EXPORT_SYMBOL_GPL(rdev_clear_badblocks);
 
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 1c2063ccf48..7b4a3c318ca 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -55,6 +55,7 @@ struct md_rdev {
 	int		sb_loaded;
 	__u64		sb_events;
 	sector_t	data_offset;	/* start of data in array */
+	sector_t	new_data_offset;/* only relevant while reshaping */
 	sector_t 	sb_start;	/* offset of the super block (in 512byte sectors) */
 	int		sb_size;	/* bytes in the superblock */
 	int		preferred_minor;	/* autorun support */
@@ -193,8 +194,9 @@ static inline int is_badblock(struct md_rdev *rdev, sector_t s, int sectors,
 	return 0;
 }
 extern int rdev_set_badblocks(struct md_rdev *rdev, sector_t s, int sectors,
-			      int acknowledged);
-extern int rdev_clear_badblocks(struct md_rdev *rdev, sector_t s, int sectors);
+			      int is_new);
+extern int rdev_clear_badblocks(struct md_rdev *rdev, sector_t s, int sectors,
+				int is_new);
 extern void md_ack_all_badblocks(struct badblocks *bb);
 
 struct mddev {
@@ -262,6 +264,7 @@ struct mddev {
 	sector_t			reshape_position;
 	int				delta_disks, new_level, new_layout;
 	int				new_chunk_sectors;
+	int				reshape_backwards;
 
 	atomic_t			plug_cnt;	/* If device is expecting
 							 * more bios soon.
@@ -390,10 +393,13 @@ struct mddev {
 						 * For external metadata, offset
 						 * from start of device. 
 						 */
+		unsigned long		space; /* space available at this offset */
 		loff_t			default_offset; /* this is the offset to use when
 							 * hot-adding a bitmap.  It should
 							 * eventually be settable by sysfs.
 							 */
+		unsigned long		default_space; /* space available at
+							* default offset */
 		struct mutex		mutex;
 		unsigned long		chunksize;
 		unsigned long		daemon_sleep; /* how many jiffies between updates? */
@@ -591,6 +597,7 @@ extern void md_write_start(struct mddev *mddev, struct bio *bi);
 extern void md_write_end(struct mddev *mddev);
 extern void md_done_sync(struct mddev *mddev, int blocks, int ok);
 extern void md_error(struct mddev *mddev, struct md_rdev *rdev);
+extern void md_finish_reshape(struct mddev *mddev);
 
 extern int mddev_congested(struct mddev *mddev, int bits);
 extern void md_flush_request(struct mddev *mddev, struct bio *bio);
@@ -615,6 +622,7 @@ extern int md_run(struct mddev *mddev);
 extern void md_stop(struct mddev *mddev);
 extern void md_stop_writes(struct mddev *mddev);
 extern int md_rdev_init(struct md_rdev *rdev);
+extern void md_rdev_clear(struct md_rdev *rdev);
 
 extern void mddev_suspend(struct mddev *mddev);
 extern void mddev_resume(struct mddev *mddev);
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 15dd59b84e9..835de7168cd 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1859,7 +1859,9 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
 
 			rdev = conf->mirrors[d].rdev;
 			if (rdev &&
-			    test_bit(In_sync, &rdev->flags) &&
+			    (test_bit(In_sync, &rdev->flags) ||
+			     (!test_bit(Faulty, &rdev->flags) &&
+			      rdev->recovery_offset >= sect + s)) &&
 			    is_badblock(rdev, sect, s,
 					&first_bad, &bad_sectors) == 0 &&
 			    sync_page_io(rdev, sect, s<<9,
@@ -2024,7 +2026,7 @@ static void handle_sync_write_finished(struct r1conf *conf, struct r1bio *r1_bio
 			continue;
 		if (test_bit(BIO_UPTODATE, &bio->bi_flags) &&
 		    test_bit(R1BIO_MadeGood, &r1_bio->state)) {
-			rdev_clear_badblocks(rdev, r1_bio->sector, s);
+			rdev_clear_badblocks(rdev, r1_bio->sector, s, 0);
 		}
 		if (!test_bit(BIO_UPTODATE, &bio->bi_flags) &&
 		    test_bit(R1BIO_WriteError, &r1_bio->state)) {
@@ -2044,7 +2046,7 @@ static void handle_write_finished(struct r1conf *conf, struct r1bio *r1_bio)
 			struct md_rdev *rdev = conf->mirrors[m].rdev;
 			rdev_clear_badblocks(rdev,
 					     r1_bio->sector,
-					     r1_bio->sectors);
+					     r1_bio->sectors, 0);
 			rdev_dec_pending(rdev, conf->mddev);
 		} else if (r1_bio->bios[m] != NULL) {
 			/* This drive got a write error.  We need to
@@ -2598,7 +2600,8 @@ static struct r1conf *setup_conf(struct mddev *mddev)
 		if (!disk->rdev ||
 		    !test_bit(In_sync, &disk->rdev->flags)) {
 			disk->head_position = 0;
-			if (disk->rdev)
+			if (disk->rdev &&
+			    (disk->rdev->saved_raid_disk < 0))
 				conf->fullsync = 1;
 		} else if (conf->last_used < 0)
 			/*
@@ -2750,9 +2753,16 @@ static int raid1_resize(struct mddev *mddev, sector_t sectors)
 	 * any io in the removed space completes, but it hardly seems
 	 * worth it.
 	 */
-	md_set_array_sectors(mddev, raid1_size(mddev, sectors, 0));
-	if (mddev->array_sectors > raid1_size(mddev, sectors, 0))
+	sector_t newsize = raid1_size(mddev, sectors, 0);
+	if (mddev->external_size &&
+	    mddev->array_sectors > newsize)
 		return -EINVAL;
+	if (mddev->bitmap) {
+		int ret = bitmap_resize(mddev->bitmap, newsize, 0, 0);
+		if (ret)
+			return ret;
+	}
+	md_set_array_sectors(mddev, newsize);
 	set_capacity(mddev->gendisk, mddev->array_sectors);
 	revalidate_disk(mddev->gendisk);
 	if (sectors > mddev->dev_sectors &&
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 3f91c2e1dfe..987db37cb87 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -24,6 +24,7 @@
 #include <linux/module.h>
 #include <linux/seq_file.h>
 #include <linux/ratelimit.h>
+#include <linux/kthread.h>
 #include "md.h"
 #include "raid10.h"
 #include "raid0.h"
@@ -68,6 +69,11 @@ static int max_queued_requests = 1024;
 static void allow_barrier(struct r10conf *conf);
 static void lower_barrier(struct r10conf *conf);
 static int enough(struct r10conf *conf, int ignore);
+static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
+				int *skipped);
+static void reshape_request_write(struct mddev *mddev, struct r10bio *r10_bio);
+static void end_reshape_write(struct bio *bio, int error);
+static void end_reshape(struct r10conf *conf);
 
 static void * r10bio_pool_alloc(gfp_t gfp_flags, void *data)
 {
@@ -112,7 +118,8 @@ static void * r10buf_pool_alloc(gfp_t gfp_flags, void *data)
 	if (!r10_bio)
 		return NULL;
 
-	if (test_bit(MD_RECOVERY_SYNC, &conf->mddev->recovery))
+	if (test_bit(MD_RECOVERY_SYNC, &conf->mddev->recovery) ||
+	    test_bit(MD_RECOVERY_RESHAPE, &conf->mddev->recovery))
 		nalloc = conf->copies; /* resync */
 	else
 		nalloc = 2; /* recovery */
@@ -140,9 +147,10 @@ static void * r10buf_pool_alloc(gfp_t gfp_flags, void *data)
 		struct bio *rbio = r10_bio->devs[j].repl_bio;
 		bio = r10_bio->devs[j].bio;
 		for (i = 0; i < RESYNC_PAGES; i++) {
-			if (j == 1 && !test_bit(MD_RECOVERY_SYNC,
-						&conf->mddev->recovery)) {
-				/* we can share bv_page's during recovery */
+			if (j > 0 && !test_bit(MD_RECOVERY_SYNC,
+					       &conf->mddev->recovery)) {
+				/* we can share bv_page's during recovery
+				 * and reshape */
 				struct bio *rbio = r10_bio->devs[0].bio;
 				page = rbio->bi_io_vec[i].bv_page;
 				get_page(page);
@@ -165,10 +173,11 @@ out_free_pages:
 	while (j--)
 		for (i = 0; i < RESYNC_PAGES ; i++)
 			safe_put_page(r10_bio->devs[j].bio->bi_io_vec[i].bv_page);
-	j = -1;
+	j = 0;
 out_free_bio:
-	while (++j < nalloc) {
-		bio_put(r10_bio->devs[j].bio);
+	for ( ; j < nalloc; j++) {
+		if (r10_bio->devs[j].bio)
+			bio_put(r10_bio->devs[j].bio);
 		if (r10_bio->devs[j].repl_bio)
 			bio_put(r10_bio->devs[j].repl_bio);
 	}
@@ -504,79 +513,96 @@ static void raid10_end_write_request(struct bio *bio, int error)
  * sector offset to a virtual address
  */
 
-static void raid10_find_phys(struct r10conf *conf, struct r10bio *r10bio)
+static void __raid10_find_phys(struct geom *geo, struct r10bio *r10bio)
 {
 	int n,f;
 	sector_t sector;
 	sector_t chunk;
 	sector_t stripe;
 	int dev;
-
 	int slot = 0;
 
 	/* now calculate first sector/dev */
-	chunk = r10bio->sector >> conf->chunk_shift;
-	sector = r10bio->sector & conf->chunk_mask;
+	chunk = r10bio->sector >> geo->chunk_shift;
+	sector = r10bio->sector & geo->chunk_mask;
 
-	chunk *= conf->near_copies;
+	chunk *= geo->near_copies;
 	stripe = chunk;
-	dev = sector_div(stripe, conf->raid_disks);
-	if (conf->far_offset)
-		stripe *= conf->far_copies;
+	dev = sector_div(stripe, geo->raid_disks);
+	if (geo->far_offset)
+		stripe *= geo->far_copies;
 
-	sector += stripe << conf->chunk_shift;
+	sector += stripe << geo->chunk_shift;
 
 	/* and calculate all the others */
-	for (n=0; n < conf->near_copies; n++) {
+	for (n = 0; n < geo->near_copies; n++) {
 		int d = dev;
 		sector_t s = sector;
 		r10bio->devs[slot].addr = sector;
 		r10bio->devs[slot].devnum = d;
 		slot++;
 
-		for (f = 1; f < conf->far_copies; f++) {
-			d += conf->near_copies;
-			if (d >= conf->raid_disks)
-				d -= conf->raid_disks;
-			s += conf->stride;
+		for (f = 1; f < geo->far_copies; f++) {
+			d += geo->near_copies;
+			if (d >= geo->raid_disks)
+				d -= geo->raid_disks;
+			s += geo->stride;
 			r10bio->devs[slot].devnum = d;
 			r10bio->devs[slot].addr = s;
 			slot++;
 		}
 		dev++;
-		if (dev >= conf->raid_disks) {
+		if (dev >= geo->raid_disks) {
 			dev = 0;
-			sector += (conf->chunk_mask + 1);
+			sector += (geo->chunk_mask + 1);
 		}
 	}
-	BUG_ON(slot != conf->copies);
+}
+
+static void raid10_find_phys(struct r10conf *conf, struct r10bio *r10bio)
+{
+	struct geom *geo = &conf->geo;
+
+	if (conf->reshape_progress != MaxSector &&
+	    ((r10bio->sector >= conf->reshape_progress) !=
+	     conf->mddev->reshape_backwards)) {
+		set_bit(R10BIO_Previous, &r10bio->state);
+		geo = &conf->prev;
+	} else
+		clear_bit(R10BIO_Previous, &r10bio->state);
+
+	__raid10_find_phys(geo, r10bio);
 }
 
 static sector_t raid10_find_virt(struct r10conf *conf, sector_t sector, int dev)
 {
 	sector_t offset, chunk, vchunk;
+	/* Never use conf->prev as this is only called during resync
+	 * or recovery, so reshape isn't happening
+	 */
+	struct geom *geo = &conf->geo;
 
-	offset = sector & conf->chunk_mask;
-	if (conf->far_offset) {
+	offset = sector & geo->chunk_mask;
+	if (geo->far_offset) {
 		int fc;
-		chunk = sector >> conf->chunk_shift;
-		fc = sector_div(chunk, conf->far_copies);
-		dev -= fc * conf->near_copies;
+		chunk = sector >> geo->chunk_shift;
+		fc = sector_div(chunk, geo->far_copies);
+		dev -= fc * geo->near_copies;
 		if (dev < 0)
-			dev += conf->raid_disks;
+			dev += geo->raid_disks;
 	} else {
-		while (sector >= conf->stride) {
-			sector -= conf->stride;
-			if (dev < conf->near_copies)
-				dev += conf->raid_disks - conf->near_copies;
+		while (sector >= geo->stride) {
+			sector -= geo->stride;
+			if (dev < geo->near_copies)
+				dev += geo->raid_disks - geo->near_copies;
 			else
-				dev -= conf->near_copies;
+				dev -= geo->near_copies;
 		}
-		chunk = sector >> conf->chunk_shift;
+		chunk = sector >> geo->chunk_shift;
 	}
-	vchunk = chunk * conf->raid_disks + dev;
-	sector_div(vchunk, conf->near_copies);
-	return (vchunk << conf->chunk_shift) + offset;
+	vchunk = chunk * geo->raid_disks + dev;
+	sector_div(vchunk, geo->near_copies);
+	return (vchunk << geo->chunk_shift) + offset;
 }
 
 /**
@@ -597,10 +623,17 @@ static int raid10_mergeable_bvec(struct request_queue *q,
 	struct r10conf *conf = mddev->private;
 	sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
 	int max;
-	unsigned int chunk_sectors = mddev->chunk_sectors;
+	unsigned int chunk_sectors;
 	unsigned int bio_sectors = bvm->bi_size >> 9;
+	struct geom *geo = &conf->geo;
+
+	chunk_sectors = (conf->geo.chunk_mask & conf->prev.chunk_mask) + 1;
+	if (conf->reshape_progress != MaxSector &&
+	    ((sector >= conf->reshape_progress) !=
+	     conf->mddev->reshape_backwards))
+		geo = &conf->prev;
 
-	if (conf->near_copies < conf->raid_disks) {
+	if (geo->near_copies < geo->raid_disks) {
 		max = (chunk_sectors - ((sector & (chunk_sectors - 1))
 					+ bio_sectors)) << 9;
 		if (max < 0)
@@ -614,6 +647,12 @@ static int raid10_mergeable_bvec(struct request_queue *q,
 	if (mddev->merge_check_needed) {
 		struct r10bio r10_bio;
 		int s;
+		if (conf->reshape_progress != MaxSector) {
+			/* Cannot give any guidance during reshape */
+			if (max <= biovec->bv_len && bio_sectors == 0)
+				return biovec->bv_len;
+			return 0;
+		}
 		r10_bio.sector = sector;
 		raid10_find_phys(conf, &r10_bio);
 		rcu_read_lock();
@@ -681,6 +720,7 @@ static struct md_rdev *read_balance(struct r10conf *conf,
 	struct md_rdev *rdev, *best_rdev;
 	int do_balance;
 	int best_slot;
+	struct geom *geo = &conf->geo;
 
 	raid10_find_phys(conf, r10_bio);
 	rcu_read_lock();
@@ -761,11 +801,11 @@ retry:
 		 * sequential read speed for 'far copies' arrays.  So only
 		 * keep it for 'near' arrays, and review those later.
 		 */
-		if (conf->near_copies > 1 && !atomic_read(&rdev->nr_pending))
+		if (geo->near_copies > 1 && !atomic_read(&rdev->nr_pending))
 			break;
 
 		/* for far > 1 always use the lowest address */
-		if (conf->far_copies > 1)
+		if (geo->far_copies > 1)
 			new_distance = r10_bio->devs[slot].addr;
 		else
 			new_distance = abs(r10_bio->devs[slot].addr -
@@ -812,7 +852,10 @@ static int raid10_congested(void *data, int bits)
 	if (mddev_congested(mddev, bits))
 		return 1;
 	rcu_read_lock();
-	for (i = 0; i < conf->raid_disks && ret == 0; i++) {
+	for (i = 0;
+	     (i < conf->geo.raid_disks || i < conf->prev.raid_disks)
+		     && ret == 0;
+	     i++) {
 		struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
 		if (rdev && !test_bit(Faulty, &rdev->flags)) {
 			struct request_queue *q = bdev_get_queue(rdev->bdev);
@@ -973,13 +1016,24 @@ static void unfreeze_array(struct r10conf *conf)
 	spin_unlock_irq(&conf->resync_lock);
 }
 
+static sector_t choose_data_offset(struct r10bio *r10_bio,
+				   struct md_rdev *rdev)
+{
+	if (!test_bit(MD_RECOVERY_RESHAPE, &rdev->mddev->recovery) ||
+	    test_bit(R10BIO_Previous, &r10_bio->state))
+		return rdev->data_offset;
+	else
+		return rdev->new_data_offset;
+}
+
 static void make_request(struct mddev *mddev, struct bio * bio)
 {
 	struct r10conf *conf = mddev->private;
 	struct r10bio *r10_bio;
 	struct bio *read_bio;
 	int i;
-	int chunk_sects = conf->chunk_mask + 1;
+	sector_t chunk_mask = (conf->geo.chunk_mask & conf->prev.chunk_mask);
+	int chunk_sects = chunk_mask + 1;
 	const int rw = bio_data_dir(bio);
 	const unsigned long do_sync = (bio->bi_rw & REQ_SYNC);
 	const unsigned long do_fua = (bio->bi_rw & REQ_FUA);
@@ -988,6 +1042,7 @@ static void make_request(struct mddev *mddev, struct bio * bio)
 	int plugged;
 	int sectors_handled;
 	int max_sectors;
+	int sectors;
 
 	if (unlikely(bio->bi_rw & REQ_FLUSH)) {
 		md_flush_request(mddev, bio);
@@ -997,9 +1052,10 @@ static void make_request(struct mddev *mddev, struct bio * bio)
 	/* If this request crosses a chunk boundary, we need to
 	 * split it.  This will only happen for 1 PAGE (or less) requests.
 	 */
-	if (unlikely( (bio->bi_sector & conf->chunk_mask) + (bio->bi_size >> 9)
-		      > chunk_sects &&
-		    conf->near_copies < conf->raid_disks)) {
+	if (unlikely((bio->bi_sector & chunk_mask) + (bio->bi_size >> 9)
+		     > chunk_sects
+		     && (conf->geo.near_copies < conf->geo.raid_disks
+			 || conf->prev.near_copies < conf->prev.raid_disks))) {
 		struct bio_pair *bp;
 		/* Sanity check -- queue functions should prevent this happening */
 		if (bio->bi_vcnt != 1 ||
@@ -1051,10 +1107,41 @@ static void make_request(struct mddev *mddev, struct bio * bio)
 	 */
 	wait_barrier(conf);
 
+	sectors = bio->bi_size >> 9;
+	while (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
+	    bio->bi_sector < conf->reshape_progress &&
+	    bio->bi_sector + sectors > conf->reshape_progress) {
+		/* IO spans the reshape position.  Need to wait for
+		 * reshape to pass
+		 */
+		allow_barrier(conf);
+		wait_event(conf->wait_barrier,
+			   conf->reshape_progress <= bio->bi_sector ||
+			   conf->reshape_progress >= bio->bi_sector + sectors);
+		wait_barrier(conf);
+	}
+	if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
+	    bio_data_dir(bio) == WRITE &&
+	    (mddev->reshape_backwards
+	     ? (bio->bi_sector < conf->reshape_safe &&
+		bio->bi_sector + sectors > conf->reshape_progress)
+	     : (bio->bi_sector + sectors > conf->reshape_safe &&
+		bio->bi_sector < conf->reshape_progress))) {
+		/* Need to update reshape_position in metadata */
+		mddev->reshape_position = conf->reshape_progress;
+		set_bit(MD_CHANGE_DEVS, &mddev->flags);
+		set_bit(MD_CHANGE_PENDING, &mddev->flags);
+		md_wakeup_thread(mddev->thread);
+		wait_event(mddev->sb_wait,
+			   !test_bit(MD_CHANGE_PENDING, &mddev->flags));
+
+		conf->reshape_safe = mddev->reshape_position;
+	}
+
 	r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);
 
 	r10_bio->master_bio = bio;
-	r10_bio->sectors = bio->bi_size >> 9;
+	r10_bio->sectors = sectors;
 
 	r10_bio->mddev = mddev;
 	r10_bio->sector = bio->bi_sector;
@@ -1093,7 +1180,7 @@ read_again:
 		r10_bio->devs[slot].rdev = rdev;
 
 		read_bio->bi_sector = r10_bio->devs[slot].addr +
-			rdev->data_offset;
+			choose_data_offset(r10_bio, rdev);
 		read_bio->bi_bdev = rdev->bdev;
 		read_bio->bi_end_io = raid10_end_read_request;
 		read_bio->bi_rw = READ | do_sync;
@@ -1297,7 +1384,8 @@ retry_write:
 		r10_bio->devs[i].bio = mbio;
 
 		mbio->bi_sector	= (r10_bio->devs[i].addr+
-				   conf->mirrors[d].rdev->data_offset);
+				   choose_data_offset(r10_bio,
+						      conf->mirrors[d].rdev));
 		mbio->bi_bdev = conf->mirrors[d].rdev->bdev;
 		mbio->bi_end_io	= raid10_end_write_request;
 		mbio->bi_rw = WRITE | do_sync | do_fua;
@@ -1321,8 +1409,10 @@ retry_write:
 		 * so it cannot disappear, so the replacement cannot
 		 * become NULL here
 		 */
-		mbio->bi_sector	= (r10_bio->devs[i].addr+
-				   conf->mirrors[d].replacement->data_offset);
+		mbio->bi_sector	= (r10_bio->devs[i].addr +
+				   choose_data_offset(
+					   r10_bio,
+					   conf->mirrors[d].replacement));
 		mbio->bi_bdev = conf->mirrors[d].replacement->bdev;
 		mbio->bi_end_io	= raid10_end_write_request;
 		mbio->bi_rw = WRITE | do_sync | do_fua;
@@ -1368,19 +1458,19 @@ static void status(struct seq_file *seq, struct mddev *mddev)
 	struct r10conf *conf = mddev->private;
 	int i;
 
-	if (conf->near_copies < conf->raid_disks)
+	if (conf->geo.near_copies < conf->geo.raid_disks)
 		seq_printf(seq, " %dK chunks", mddev->chunk_sectors / 2);
-	if (conf->near_copies > 1)
-		seq_printf(seq, " %d near-copies", conf->near_copies);
-	if (conf->far_copies > 1) {
-		if (conf->far_offset)
-			seq_printf(seq, " %d offset-copies", conf->far_copies);
+	if (conf->geo.near_copies > 1)
+		seq_printf(seq, " %d near-copies", conf->geo.near_copies);
+	if (conf->geo.far_copies > 1) {
+		if (conf->geo.far_offset)
+			seq_printf(seq, " %d offset-copies", conf->geo.far_copies);
 		else
-			seq_printf(seq, " %d far-copies", conf->far_copies);
+			seq_printf(seq, " %d far-copies", conf->geo.far_copies);
 	}
-	seq_printf(seq, " [%d/%d] [", conf->raid_disks,
-					conf->raid_disks - mddev->degraded);
-	for (i = 0; i < conf->raid_disks; i++)
+	seq_printf(seq, " [%d/%d] [", conf->geo.raid_disks,
+					conf->geo.raid_disks - mddev->degraded);
+	for (i = 0; i < conf->geo.raid_disks; i++)
 		seq_printf(seq, "%s",
 			      conf->mirrors[i].rdev &&
 			      test_bit(In_sync, &conf->mirrors[i].rdev->flags) ? "U" : "_");
@@ -1392,7 +1482,7 @@ static void status(struct seq_file *seq, struct mddev *mddev)
  * Don't consider the device numbered 'ignore'
  * as we might be about to remove it.
  */
-static int enough(struct r10conf *conf, int ignore)
+static int _enough(struct r10conf *conf, struct geom *geo, int ignore)
 {
 	int first = 0;
 
@@ -1403,7 +1493,7 @@ static int enough(struct r10conf *conf, int ignore)
 			if (conf->mirrors[first].rdev &&
 			    first != ignore)
 				cnt++;
-			first = (first+1) % conf->raid_disks;
+			first = (first+1) % geo->raid_disks;
 		}
 		if (cnt == 0)
 			return 0;
@@ -1411,6 +1501,12 @@ static int enough(struct r10conf *conf, int ignore)
 	return 1;
 }
 
+static int enough(struct r10conf *conf, int ignore)
+{
+	return _enough(conf, &conf->geo, ignore) &&
+		_enough(conf, &conf->prev, ignore);
+}
+
 static void error(struct mddev *mddev, struct md_rdev *rdev)
 {
 	char b[BDEVNAME_SIZE];
@@ -1445,7 +1541,7 @@ static void error(struct mddev *mddev, struct md_rdev *rdev)
 	       "md/raid10:%s: Disk failure on %s, disabling device.\n"
 	       "md/raid10:%s: Operation continuing on %d devices.\n",
 	       mdname(mddev), bdevname(rdev->bdev, b),
-	       mdname(mddev), conf->raid_disks - mddev->degraded);
+	       mdname(mddev), conf->geo.raid_disks - mddev->degraded);
 }
 
 static void print_conf(struct r10conf *conf)
@@ -1458,10 +1554,10 @@ static void print_conf(struct r10conf *conf)
 		printk(KERN_DEBUG "(!conf)\n");
 		return;
 	}
-	printk(KERN_DEBUG " --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
-		conf->raid_disks);
+	printk(KERN_DEBUG " --- wd:%d rd:%d\n", conf->geo.raid_disks - conf->mddev->degraded,
+		conf->geo.raid_disks);
 
-	for (i = 0; i < conf->raid_disks; i++) {
+	for (i = 0; i < conf->geo.raid_disks; i++) {
 		char b[BDEVNAME_SIZE];
 		tmp = conf->mirrors + i;
 		if (tmp->rdev)
@@ -1493,7 +1589,7 @@ static int raid10_spare_active(struct mddev *mddev)
 	 * Find all non-in_sync disks within the RAID10 configuration
 	 * and mark them in_sync
 	 */
-	for (i = 0; i < conf->raid_disks; i++) {
+	for (i = 0; i < conf->geo.raid_disks; i++) {
 		tmp = conf->mirrors + i;
 		if (tmp->replacement
 		    && tmp->replacement->recovery_offset == MaxSector
@@ -1535,7 +1631,7 @@ static int raid10_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 	int err = -EEXIST;
 	int mirror;
 	int first = 0;
-	int last = conf->raid_disks - 1;
+	int last = conf->geo.raid_disks - 1;
 	struct request_queue *q = bdev_get_queue(rdev->bdev);
 
 	if (mddev->recovery_cp < MaxSector)
@@ -1543,7 +1639,7 @@ static int raid10_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 		 * very different from resync
 		 */
 		return -EBUSY;
-	if (rdev->saved_raid_disk < 0 && !enough(conf, -1))
+	if (rdev->saved_raid_disk < 0 && !_enough(conf, &conf->prev, -1))
 		return -EINVAL;
 
 	if (rdev->raid_disk >= 0)
@@ -1635,6 +1731,7 @@ static int raid10_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 	if (!test_bit(Faulty, &rdev->flags) &&
 	    mddev->recovery_disabled != p->recovery_disabled &&
 	    (!p->replacement || p->replacement == rdev) &&
+	    number < conf->geo.raid_disks &&
 	    enough(conf, -1)) {
 		err = -EBUSY;
 		goto abort;
@@ -1676,7 +1773,11 @@ static void end_sync_read(struct bio *bio, int error)
 	struct r10conf *conf = r10_bio->mddev->private;
 	int d;
 
-	d = find_bio_disk(conf, r10_bio, bio, NULL, NULL);
+	if (bio == r10_bio->master_bio) {
+		/* this is a reshape read */
+		d = r10_bio->read_slot; /* really the read dev */
+	} else
+		d = find_bio_disk(conf, r10_bio, bio, NULL, NULL);
 
 	if (test_bit(BIO_UPTODATE, &bio->bi_flags))
 		set_bit(R10BIO_Uptodate, &r10_bio->state);
@@ -2218,7 +2319,9 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 				       " (%d sectors at %llu on %s)\n",
 				       mdname(mddev), s,
 				       (unsigned long long)(
-					       sect + rdev->data_offset),
+					       sect +
+					       choose_data_offset(r10_bio,
+								  rdev)),
 				       bdevname(rdev->bdev, b));
 				printk(KERN_NOTICE "md/raid10:%s: %s: failing "
 				       "drive\n",
@@ -2256,7 +2359,8 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 				       " (%d sectors at %llu on %s)\n",
 				       mdname(mddev), s,
 				       (unsigned long long)(
-					       sect + rdev->data_offset),
+					       sect +
+					       choose_data_offset(r10_bio, rdev)),
 				       bdevname(rdev->bdev, b));
 				printk(KERN_NOTICE "md/raid10:%s: %s: failing "
 				       "drive\n",
@@ -2269,7 +2373,8 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 				       " (%d sectors at %llu on %s)\n",
 				       mdname(mddev), s,
 				       (unsigned long long)(
-					       sect + rdev->data_offset),
+					       sect +
+					       choose_data_offset(r10_bio, rdev)),
 				       bdevname(rdev->bdev, b));
 				atomic_add(s, &rdev->corrected_errors);
 			}
@@ -2343,7 +2448,7 @@ static int narrow_write_error(struct r10bio *r10_bio, int i)
 		wbio = bio_clone_mddev(bio, GFP_NOIO, mddev);
 		md_trim_bio(wbio, sector - bio->bi_sector, sectors);
 		wbio->bi_sector = (r10_bio->devs[i].addr+
-				   rdev->data_offset+
+				   choose_data_offset(r10_bio, rdev) +
 				   (sector - r10_bio->sector));
 		wbio->bi_bdev = rdev->bdev;
 		if (submit_bio_wait(WRITE, wbio) == 0)
@@ -2420,7 +2525,7 @@ read_more:
 	r10_bio->devs[slot].bio = bio;
 	r10_bio->devs[slot].rdev = rdev;
 	bio->bi_sector = r10_bio->devs[slot].addr
-		+ rdev->data_offset;
+		+ choose_data_offset(r10_bio, rdev);
 	bio->bi_bdev = rdev->bdev;
 	bio->bi_rw = READ | do_sync;
 	bio->bi_private = r10_bio;
@@ -2480,7 +2585,7 @@ static void handle_write_completed(struct r10conf *conf, struct r10bio *r10_bio)
 				rdev_clear_badblocks(
 					rdev,
 					r10_bio->devs[m].addr,
-					r10_bio->sectors);
+					r10_bio->sectors, 0);
 			} else {
 				if (!rdev_set_badblocks(
 					    rdev,
@@ -2496,7 +2601,7 @@ static void handle_write_completed(struct r10conf *conf, struct r10bio *r10_bio)
 				rdev_clear_badblocks(
 					rdev,
 					r10_bio->devs[m].addr,
-					r10_bio->sectors);
+					r10_bio->sectors, 0);
 			} else {
 				if (!rdev_set_badblocks(
 					    rdev,
@@ -2515,7 +2620,7 @@ static void handle_write_completed(struct r10conf *conf, struct r10bio *r10_bio)
 				rdev_clear_badblocks(
 					rdev,
 					r10_bio->devs[m].addr,
-					r10_bio->sectors);
+					r10_bio->sectors, 0);
 				rdev_dec_pending(rdev, conf->mddev);
 			} else if (bio != NULL &&
 				   !test_bit(BIO_UPTODATE, &bio->bi_flags)) {
@@ -2532,7 +2637,7 @@ static void handle_write_completed(struct r10conf *conf, struct r10bio *r10_bio)
 				rdev_clear_badblocks(
 					rdev,
 					r10_bio->devs[m].addr,
-					r10_bio->sectors);
+					r10_bio->sectors, 0);
 				rdev_dec_pending(rdev, conf->mddev);
 			}
 		}
@@ -2573,6 +2678,8 @@ static void raid10d(struct mddev *mddev)
 		if (test_bit(R10BIO_MadeGood, &r10_bio->state) ||
 		    test_bit(R10BIO_WriteError, &r10_bio->state))
 			handle_write_completed(conf, r10_bio);
+		else if (test_bit(R10BIO_IsReshape, &r10_bio->state))
+			reshape_request_write(mddev, r10_bio);
 		else if (test_bit(R10BIO_IsSync, &r10_bio->state))
 			sync_request_write(mddev, r10_bio);
 		else if (test_bit(R10BIO_IsRecover, &r10_bio->state))
@@ -2603,7 +2710,7 @@ static int init_resync(struct r10conf *conf)
 	buffs = RESYNC_WINDOW / RESYNC_BLOCK_SIZE;
 	BUG_ON(conf->r10buf_pool);
 	conf->have_replacement = 0;
-	for (i = 0; i < conf->raid_disks; i++)
+	for (i = 0; i < conf->geo.raid_disks; i++)
 		if (conf->mirrors[i].replacement)
 			conf->have_replacement = 1;
 	conf->r10buf_pool = mempool_create(buffs, r10buf_pool_alloc, r10buf_pool_free, conf);
@@ -2657,6 +2764,7 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 	sector_t sync_blocks;
 	sector_t sectors_skipped = 0;
 	int chunks_skipped = 0;
+	sector_t chunk_mask = conf->geo.chunk_mask;
 
 	if (!conf->r10buf_pool)
 		if (init_resync(conf))
@@ -2664,7 +2772,8 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 
  skipped:
 	max_sector = mddev->dev_sectors;
-	if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
+	if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) ||
+	    test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
 		max_sector = mddev->resync_max_sectors;
 	if (sector_nr >= max_sector) {
 		/* If we aborted, we need to abort the
@@ -2676,11 +2785,16 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 		 * we need to convert that to several
 		 * virtual addresses.
 		 */
+		if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery)) {
+			end_reshape(conf);
+			return 0;
+		}
+
 		if (mddev->curr_resync < max_sector) { /* aborted */
 			if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
 				bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
 						&sync_blocks, 1);
-			else for (i=0; i<conf->raid_disks; i++) {
+			else for (i = 0; i < conf->geo.raid_disks; i++) {
 				sector_t sect =
 					raid10_find_virt(conf, mddev->curr_resync, i);
 				bitmap_end_sync(mddev->bitmap, sect,
@@ -2694,7 +2808,7 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 				/* Completed a full sync so the replacements
 				 * are now fully recovered.
 				 */
-				for (i = 0; i < conf->raid_disks; i++)
+				for (i = 0; i < conf->geo.raid_disks; i++)
 					if (conf->mirrors[i].replacement)
 						conf->mirrors[i].replacement
 							->recovery_offset
@@ -2707,7 +2821,11 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 		*skipped = 1;
 		return sectors_skipped;
 	}
-	if (chunks_skipped >= conf->raid_disks) {
+
+	if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
+		return reshape_request(mddev, sector_nr, skipped);
+
+	if (chunks_skipped >= conf->geo.raid_disks) {
 		/* if there has been nothing to do on any drive,
 		 * then there is nothing to do at all..
 		 */
@@ -2721,9 +2839,9 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 	/* make sure whole request will fit in a chunk - if chunks
 	 * are meaningful
 	 */
-	if (conf->near_copies < conf->raid_disks &&
-	    max_sector > (sector_nr | conf->chunk_mask))
-		max_sector = (sector_nr | conf->chunk_mask) + 1;
+	if (conf->geo.near_copies < conf->geo.raid_disks &&
+	    max_sector > (sector_nr | chunk_mask))
+		max_sector = (sector_nr | chunk_mask) + 1;
 	/*
 	 * If there is non-resync activity waiting for us then
 	 * put in a delay to throttle resync.
@@ -2752,7 +2870,7 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 		int j;
 		r10_bio = NULL;
 
-		for (i=0 ; i<conf->raid_disks; i++) {
+		for (i = 0 ; i < conf->geo.raid_disks; i++) {
 			int still_degraded;
 			struct r10bio *rb2;
 			sector_t sect;
@@ -2806,7 +2924,7 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 			/* Need to check if the array will still be
 			 * degraded
 			 */
-			for (j=0; j<conf->raid_disks; j++)
+			for (j = 0; j < conf->geo.raid_disks; j++)
 				if (conf->mirrors[j].rdev == NULL ||
 				    test_bit(Faulty, &conf->mirrors[j].rdev->flags)) {
 					still_degraded = 1;
@@ -2984,9 +3102,9 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 		r10_bio->sector = sector_nr;
 		set_bit(R10BIO_IsSync, &r10_bio->state);
 		raid10_find_phys(conf, r10_bio);
-		r10_bio->sectors = (sector_nr | conf->chunk_mask) - sector_nr +1;
+		r10_bio->sectors = (sector_nr | chunk_mask) - sector_nr + 1;
 
-		for (i=0; i<conf->copies; i++) {
+		for (i = 0; i < conf->copies; i++) {
 			int d = r10_bio->devs[i].devnum;
 			sector_t first_bad, sector;
 			int bad_sectors;
@@ -3152,16 +3270,17 @@ raid10_size(struct mddev *mddev, sector_t sectors, int raid_disks)
 	struct r10conf *conf = mddev->private;
 
 	if (!raid_disks)
-		raid_disks = conf->raid_disks;
+		raid_disks = min(conf->geo.raid_disks,
+				 conf->prev.raid_disks);
 	if (!sectors)
 		sectors = conf->dev_sectors;
 
-	size = sectors >> conf->chunk_shift;
-	sector_div(size, conf->far_copies);
+	size = sectors >> conf->geo.chunk_shift;
+	sector_div(size, conf->geo.far_copies);
 	size = size * raid_disks;
-	sector_div(size, conf->near_copies);
+	sector_div(size, conf->geo.near_copies);
 
-	return size << conf->chunk_shift;
+	return size << conf->geo.chunk_shift;
 }
 
 static void calc_sectors(struct r10conf *conf, sector_t size)
@@ -3171,10 +3290,10 @@ static void calc_sectors(struct r10conf *conf, sector_t size)
 	 * conf->stride
 	 */
 
-	size = size >> conf->chunk_shift;
-	sector_div(size, conf->far_copies);
-	size = size * conf->raid_disks;
-	sector_div(size, conf->near_copies);
+	size = size >> conf->geo.chunk_shift;
+	sector_div(size, conf->geo.far_copies);
+	size = size * conf->geo.raid_disks;
+	sector_div(size, conf->geo.near_copies);
 	/* 'size' is now the number of chunks in the array */
 	/* calculate "used chunks per device" */
 	size = size * conf->copies;
@@ -3182,38 +3301,76 @@ static void calc_sectors(struct r10conf *conf, sector_t size)
 	/* We need to round up when dividing by raid_disks to
 	 * get the stride size.
 	 */
-	size = DIV_ROUND_UP_SECTOR_T(size, conf->raid_disks);
+	size = DIV_ROUND_UP_SECTOR_T(size, conf->geo.raid_disks);
 
-	conf->dev_sectors = size << conf->chunk_shift;
+	conf->dev_sectors = size << conf->geo.chunk_shift;
 
-	if (conf->far_offset)
-		conf->stride = 1 << conf->chunk_shift;
+	if (conf->geo.far_offset)
+		conf->geo.stride = 1 << conf->geo.chunk_shift;
 	else {
-		sector_div(size, conf->far_copies);
-		conf->stride = size << conf->chunk_shift;
+		sector_div(size, conf->geo.far_copies);
+		conf->geo.stride = size << conf->geo.chunk_shift;
 	}
 }
 
+enum geo_type {geo_new, geo_old, geo_start};
+static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new)
+{
+	int nc, fc, fo;
+	int layout, chunk, disks;
+	switch (new) {
+	case geo_old:
+		layout = mddev->layout;
+		chunk = mddev->chunk_sectors;
+		disks = mddev->raid_disks - mddev->delta_disks;
+		break;
+	case geo_new:
+		layout = mddev->new_layout;
+		chunk = mddev->new_chunk_sectors;
+		disks = mddev->raid_disks;
+		break;
+	default: /* avoid 'may be unused' warnings */
+	case geo_start: /* new when starting reshape - raid_disks not
+			 * updated yet. */
+		layout = mddev->new_layout;
+		chunk = mddev->new_chunk_sectors;
+		disks = mddev->raid_disks + mddev->delta_disks;
+		break;
+	}
+	if (layout >> 17)
+		return -1;
+	if (chunk < (PAGE_SIZE >> 9) ||
+	    !is_power_of_2(chunk))
+		return -2;
+	nc = layout & 255;
+	fc = (layout >> 8) & 255;
+	fo = layout & (1<<16);
+	geo->raid_disks = disks;
+	geo->near_copies = nc;
+	geo->far_copies = fc;
+	geo->far_offset = fo;
+	geo->chunk_mask = chunk - 1;
+	geo->chunk_shift = ffz(~chunk);
+	return nc*fc;
+}
+
 static struct r10conf *setup_conf(struct mddev *mddev)
 {
 	struct r10conf *conf = NULL;
-	int nc, fc, fo;
 	int err = -EINVAL;
+	struct geom geo;
+	int copies;
+
+	copies = setup_geo(&geo, mddev, geo_new);
 
-	if (mddev->new_chunk_sectors < (PAGE_SIZE >> 9) ||
-	    !is_power_of_2(mddev->new_chunk_sectors)) {
+	if (copies == -2) {
 		printk(KERN_ERR "md/raid10:%s: chunk size must be "
 		       "at least PAGE_SIZE(%ld) and be a power of 2.\n",
 		       mdname(mddev), PAGE_SIZE);
 		goto out;
 	}
 
-	nc = mddev->new_layout & 255;
-	fc = (mddev->new_layout >> 8) & 255;
-	fo = mddev->new_layout & (1<<16);
-
-	if ((nc*fc) <2 || (nc*fc) > mddev->raid_disks ||
-	    (mddev->new_layout >> 17)) {
+	if (copies < 2 || copies > mddev->raid_disks) {
 		printk(KERN_ERR "md/raid10:%s: unsupported raid10 layout: 0x%8x\n",
 		       mdname(mddev), mddev->new_layout);
 		goto out;
@@ -3224,7 +3381,9 @@ static struct r10conf *setup_conf(struct mddev *mddev)
 	if (!conf)
 		goto out;
 
-	conf->mirrors = kzalloc(sizeof(struct mirror_info)*mddev->raid_disks,
+	/* FIXME calc properly */
+	conf->mirrors = kzalloc(sizeof(struct mirror_info)*(mddev->raid_disks +
+							    max(0,mddev->delta_disks)),
 				GFP_KERNEL);
 	if (!conf->mirrors)
 		goto out;
@@ -3233,22 +3392,29 @@ static struct r10conf *setup_conf(struct mddev *mddev)
 	if (!conf->tmppage)
 		goto out;
 
-
-	conf->raid_disks = mddev->raid_disks;
-	conf->near_copies = nc;
-	conf->far_copies = fc;
-	conf->copies = nc*fc;
-	conf->far_offset = fo;
-	conf->chunk_mask = mddev->new_chunk_sectors - 1;
-	conf->chunk_shift = ffz(~mddev->new_chunk_sectors);
-
+	conf->geo = geo;
+	conf->copies = copies;
 	conf->r10bio_pool = mempool_create(NR_RAID10_BIOS, r10bio_pool_alloc,
 					   r10bio_pool_free, conf);
 	if (!conf->r10bio_pool)
 		goto out;
 
 	calc_sectors(conf, mddev->dev_sectors);
-
+	if (mddev->reshape_position == MaxSector) {
+		conf->prev = conf->geo;
+		conf->reshape_progress = MaxSector;
+	} else {
+		if (setup_geo(&conf->prev, mddev, geo_old) != conf->copies) {
+			err = -EINVAL;
+			goto out;
+		}
+		conf->reshape_progress = mddev->reshape_position;
+		if (conf->prev.far_offset)
+			conf->prev.stride = 1 << conf->prev.chunk_shift;
+		else
+			/* far_copies must be 1 */
+			conf->prev.stride = conf->dev_sectors;
+	}
 	spin_lock_init(&conf->device_lock);
 	INIT_LIST_HEAD(&conf->retry_list);
 
@@ -3263,8 +3429,9 @@ static struct r10conf *setup_conf(struct mddev *mddev)
 	return conf;
 
  out:
-	printk(KERN_ERR "md/raid10:%s: couldn't allocate memory.\n",
-	       mdname(mddev));
+	if (err == -ENOMEM)
+		printk(KERN_ERR "md/raid10:%s: couldn't allocate memory.\n",
+		       mdname(mddev));
 	if (conf) {
 		if (conf->r10bio_pool)
 			mempool_destroy(conf->r10bio_pool);
@@ -3282,12 +3449,8 @@ static int run(struct mddev *mddev)
 	struct mirror_info *disk;
 	struct md_rdev *rdev;
 	sector_t size;
-
-	/*
-	 * copy the already verified devices into our private RAID10
-	 * bookkeeping area. [whatever we allocate in run(),
-	 * should be freed in stop()]
-	 */
+	sector_t min_offset_diff = 0;
+	int first = 1;
 
 	if (mddev->private == NULL) {
 		conf = setup_conf(mddev);
@@ -3304,17 +3467,20 @@ static int run(struct mddev *mddev)
 
 	chunk_size = mddev->chunk_sectors << 9;
 	blk_queue_io_min(mddev->queue, chunk_size);
-	if (conf->raid_disks % conf->near_copies)
-		blk_queue_io_opt(mddev->queue, chunk_size * conf->raid_disks);
+	if (conf->geo.raid_disks % conf->geo.near_copies)
+		blk_queue_io_opt(mddev->queue, chunk_size * conf->geo.raid_disks);
 	else
 		blk_queue_io_opt(mddev->queue, chunk_size *
-				 (conf->raid_disks / conf->near_copies));
+				 (conf->geo.raid_disks / conf->geo.near_copies));
 
 	rdev_for_each(rdev, mddev) {
+		long long diff;
 
 		disk_idx = rdev->raid_disk;
-		if (disk_idx >= conf->raid_disks
-		    || disk_idx < 0)
+		if (disk_idx < 0)
+			continue;
+		if (disk_idx >= conf->geo.raid_disks &&
+		    disk_idx >= conf->prev.raid_disks)
 			continue;
 		disk = conf->mirrors + disk_idx;
 
@@ -3327,12 +3493,20 @@ static int run(struct mddev *mddev)
 				goto out_free_conf;
 			disk->rdev = rdev;
 		}
+		diff = (rdev->new_data_offset - rdev->data_offset);
+		if (!mddev->reshape_backwards)
+			diff = -diff;
+		if (diff < 0)
+			diff = 0;
+		if (first || diff < min_offset_diff)
+			min_offset_diff = diff;
 
 		disk_stack_limits(mddev->gendisk, rdev->bdev,
 				  rdev->data_offset << 9);
 
 		disk->head_position = 0;
 	}
+
 	/* need to check that every block has at least one working mirror */
 	if (!enough(conf, -1)) {
 		printk(KERN_ERR "md/raid10:%s: not enough operational mirrors.\n",
@@ -3340,8 +3514,21 @@ static int run(struct mddev *mddev)
 		goto out_free_conf;
 	}
 
+	if (conf->reshape_progress != MaxSector) {
+		/* must ensure that shape change is supported */
+		if (conf->geo.far_copies != 1 &&
+		    conf->geo.far_offset == 0)
+			goto out_free_conf;
+		if (conf->prev.far_copies != 1 &&
+		    conf->geo.far_offset == 0)
+			goto out_free_conf;
+	}
+
 	mddev->degraded = 0;
-	for (i = 0; i < conf->raid_disks; i++) {
+	for (i = 0;
+	     i < conf->geo.raid_disks
+		     || i < conf->prev.raid_disks;
+	     i++) {
 
 		disk = conf->mirrors + i;
 
@@ -3368,8 +3555,8 @@ static int run(struct mddev *mddev)
 		       mdname(mddev));
 	printk(KERN_INFO
 		"md/raid10:%s: active with %d out of %d devices\n",
-		mdname(mddev), conf->raid_disks - mddev->degraded,
-		conf->raid_disks);
+		mdname(mddev), conf->geo.raid_disks - mddev->degraded,
+		conf->geo.raid_disks);
 	/*
 	 * Ok, everything is just fine now
 	 */
@@ -3386,11 +3573,11 @@ static int run(struct mddev *mddev)
 	 * maybe...
 	 */
 	{
-		int stripe = conf->raid_disks *
+		int stripe = conf->geo.raid_disks *
 			((mddev->chunk_sectors << 9) / PAGE_SIZE);
-		stripe /= conf->near_copies;
-		if (mddev->queue->backing_dev_info.ra_pages < 2* stripe)
-			mddev->queue->backing_dev_info.ra_pages = 2* stripe;
+		stripe /= conf->geo.near_copies;
+		if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
+			mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
 	}
 
 	blk_queue_merge_bvec(mddev->queue, raid10_mergeable_bvec);
@@ -3398,6 +3585,30 @@ static int run(struct mddev *mddev)
 	if (md_integrity_register(mddev))
 		goto out_free_conf;
 
+	if (conf->reshape_progress != MaxSector) {
+		unsigned long before_length, after_length;
+
+		before_length = ((1 << conf->prev.chunk_shift) *
+				 conf->prev.far_copies);
+		after_length = ((1 << conf->geo.chunk_shift) *
+				conf->geo.far_copies);
+
+		if (max(before_length, after_length) > min_offset_diff) {
+			/* This cannot work */
+			printk("md/raid10: offset difference not enough to continue reshape\n");
+			goto out_free_conf;
+		}
+		conf->offset_diff = min_offset_diff;
+
+		conf->reshape_safe = conf->reshape_progress;
+		clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
+		clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
+		set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
+		set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
+		mddev->sync_thread = md_register_thread(md_do_sync, mddev,
+							"reshape");
+	}
+
 	return 0;
 
 out_free_conf:
@@ -3460,14 +3671,23 @@ static int raid10_resize(struct mddev *mddev, sector_t sectors)
 	struct r10conf *conf = mddev->private;
 	sector_t oldsize, size;
 
-	if (conf->far_copies > 1 && !conf->far_offset)
+	if (mddev->reshape_position != MaxSector)
+		return -EBUSY;
+
+	if (conf->geo.far_copies > 1 && !conf->geo.far_offset)
 		return -EINVAL;
 
 	oldsize = raid10_size(mddev, 0, 0);
 	size = raid10_size(mddev, sectors, 0);
-	md_set_array_sectors(mddev, size);
-	if (mddev->array_sectors > size)
+	if (mddev->external_size &&
+	    mddev->array_sectors > size)
 		return -EINVAL;
+	if (mddev->bitmap) {
+		int ret = bitmap_resize(mddev->bitmap, size, 0, 0);
+		if (ret)
+			return ret;
+	}
+	md_set_array_sectors(mddev, size);
 	set_capacity(mddev->gendisk, mddev->array_sectors);
 	revalidate_disk(mddev->gendisk);
 	if (sectors > mddev->dev_sectors &&
@@ -3534,6 +3754,758 @@ static void *raid10_takeover(struct mddev *mddev)
 	return ERR_PTR(-EINVAL);
 }
 
+static int raid10_check_reshape(struct mddev *mddev)
+{
+	/* Called when there is a request to change
+	 * - layout (to ->new_layout)
+	 * - chunk size (to ->new_chunk_sectors)
+	 * - raid_disks (by delta_disks)
+	 * or when trying to restart a reshape that was ongoing.
+	 *
+	 * We need to validate the request and possibly allocate
+	 * space if that might be an issue later.
+	 *
+	 * Currently we reject any reshape of a 'far' mode array,
+	 * allow chunk size to change if new is generally acceptable,
+	 * allow raid_disks to increase, and allow
+	 * a switch between 'near' mode and 'offset' mode.
+	 */
+	struct r10conf *conf = mddev->private;
+	struct geom geo;
+
+	if (conf->geo.far_copies != 1 && !conf->geo.far_offset)
+		return -EINVAL;
+
+	if (setup_geo(&geo, mddev, geo_start) != conf->copies)
+		/* mustn't change number of copies */
+		return -EINVAL;
+	if (geo.far_copies > 1 && !geo.far_offset)
+		/* Cannot switch to 'far' mode */
+		return -EINVAL;
+
+	if (mddev->array_sectors & geo.chunk_mask)
+			/* not factor of array size */
+			return -EINVAL;
+
+	if (!enough(conf, -1))
+		return -EINVAL;
+
+	kfree(conf->mirrors_new);
+	conf->mirrors_new = NULL;
+	if (mddev->delta_disks > 0) {
+		/* allocate new 'mirrors' list */
+		conf->mirrors_new = kzalloc(
+			sizeof(struct mirror_info)
+			*(mddev->raid_disks +
+			  mddev->delta_disks),
+			GFP_KERNEL);
+		if (!conf->mirrors_new)
+			return -ENOMEM;
+	}
+	return 0;
+}
+
+/*
+ * Need to check if array has failed when deciding whether to:
+ *  - start an array
+ *  - remove non-faulty devices
+ *  - add a spare
+ *  - allow a reshape
+ * This determination is simple when no reshape is happening.
+ * However if there is a reshape, we need to carefully check
+ * both the before and after sections.
+ * This is because some failed devices may only affect one
+ * of the two sections, and some non-in_sync devices may
+ * be insync in the section most affected by failed devices.
+ */
+static int calc_degraded(struct r10conf *conf)
+{
+	int degraded, degraded2;
+	int i;
+
+	rcu_read_lock();
+	degraded = 0;
+	/* 'prev' section first */
+	for (i = 0; i < conf->prev.raid_disks; i++) {
+		struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
+		if (!rdev || test_bit(Faulty, &rdev->flags))
+			degraded++;
+		else if (!test_bit(In_sync, &rdev->flags))
+			/* When we can reduce the number of devices in
+			 * an array, this might not contribute to
+			 * 'degraded'.  It does now.
+			 */
+			degraded++;
+	}
+	rcu_read_unlock();
+	if (conf->geo.raid_disks == conf->prev.raid_disks)
+		return degraded;
+	rcu_read_lock();
+	degraded2 = 0;
+	for (i = 0; i < conf->geo.raid_disks; i++) {
+		struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
+		if (!rdev || test_bit(Faulty, &rdev->flags))
+			degraded2++;
+		else if (!test_bit(In_sync, &rdev->flags)) {
+			/* If reshape is increasing the number of devices,
+			 * this section has already been recovered, so
+			 * it doesn't contribute to degraded.
+			 * else it does.
+			 */
+			if (conf->geo.raid_disks <= conf->prev.raid_disks)
+				degraded2++;
+		}
+	}
+	rcu_read_unlock();
+	if (degraded2 > degraded)
+		return degraded2;
+	return degraded;
+}
+
+static int raid10_start_reshape(struct mddev *mddev)
+{
+	/* A 'reshape' has been requested. This commits
+	 * the various 'new' fields and sets MD_RECOVER_RESHAPE
+	 * This also checks if there are enough spares and adds them
+	 * to the array.
+	 * We currently require enough spares to make the final
+	 * array non-degraded.  We also require that the difference
+	 * between old and new data_offset - on each device - is
+	 * enough that we never risk over-writing.
+	 */
+
+	unsigned long before_length, after_length;
+	sector_t min_offset_diff = 0;
+	int first = 1;
+	struct geom new;
+	struct r10conf *conf = mddev->private;
+	struct md_rdev *rdev;
+	int spares = 0;
+	int ret;
+
+	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+		return -EBUSY;
+
+	if (setup_geo(&new, mddev, geo_start) != conf->copies)
+		return -EINVAL;
+
+	before_length = ((1 << conf->prev.chunk_shift) *
+			 conf->prev.far_copies);
+	after_length = ((1 << conf->geo.chunk_shift) *
+			conf->geo.far_copies);
+
+	rdev_for_each(rdev, mddev) {
+		if (!test_bit(In_sync, &rdev->flags)
+		    && !test_bit(Faulty, &rdev->flags))
+			spares++;
+		if (rdev->raid_disk >= 0) {
+			long long diff = (rdev->new_data_offset
+					  - rdev->data_offset);
+			if (!mddev->reshape_backwards)
+				diff = -diff;
+			if (diff < 0)
+				diff = 0;
+			if (first || diff < min_offset_diff)
+				min_offset_diff = diff;
+		}
+	}
+
+	if (max(before_length, after_length) > min_offset_diff)
+		return -EINVAL;
+
+	if (spares < mddev->delta_disks)
+		return -EINVAL;
+
+	conf->offset_diff = min_offset_diff;
+	spin_lock_irq(&conf->device_lock);
+	if (conf->mirrors_new) {
+		memcpy(conf->mirrors_new, conf->mirrors,
+		       sizeof(struct mirror_info)*conf->prev.raid_disks);
+		smp_mb();
+		kfree(conf->mirrors_old); /* FIXME and elsewhere */
+		conf->mirrors_old = conf->mirrors;
+		conf->mirrors = conf->mirrors_new;
+		conf->mirrors_new = NULL;
+	}
+	setup_geo(&conf->geo, mddev, geo_start);
+	smp_mb();
+	if (mddev->reshape_backwards) {
+		sector_t size = raid10_size(mddev, 0, 0);
+		if (size < mddev->array_sectors) {
+			spin_unlock_irq(&conf->device_lock);
+			printk(KERN_ERR "md/raid10:%s: array size must be reduce before number of disks\n",
+			       mdname(mddev));
+			return -EINVAL;
+		}
+		mddev->resync_max_sectors = size;
+		conf->reshape_progress = size;
+	} else
+		conf->reshape_progress = 0;
+	spin_unlock_irq(&conf->device_lock);
+
+	if (mddev->delta_disks && mddev->bitmap) {
+		ret = bitmap_resize(mddev->bitmap,
+				    raid10_size(mddev, 0,
+						conf->geo.raid_disks),
+				    0, 0);
+		if (ret)
+			goto abort;
+	}
+	if (mddev->delta_disks > 0) {
+		rdev_for_each(rdev, mddev)
+			if (rdev->raid_disk < 0 &&
+			    !test_bit(Faulty, &rdev->flags)) {
+				if (raid10_add_disk(mddev, rdev) == 0) {
+					if (rdev->raid_disk >=
+					    conf->prev.raid_disks)
+						set_bit(In_sync, &rdev->flags);
+					else
+						rdev->recovery_offset = 0;
+
+					if (sysfs_link_rdev(mddev, rdev))
+						/* Failure here  is OK */;
+				}
+			} else if (rdev->raid_disk >= conf->prev.raid_disks
+				   && !test_bit(Faulty, &rdev->flags)) {
+				/* This is a spare that was manually added */
+				set_bit(In_sync, &rdev->flags);
+			}
+	}
+	/* When a reshape changes the number of devices,
+	 * ->degraded is measured against the larger of the
+	 * pre and  post numbers.
+	 */
+	spin_lock_irq(&conf->device_lock);
+	mddev->degraded = calc_degraded(conf);
+	spin_unlock_irq(&conf->device_lock);
+	mddev->raid_disks = conf->geo.raid_disks;
+	mddev->reshape_position = conf->reshape_progress;
+	set_bit(MD_CHANGE_DEVS, &mddev->flags);
+
+	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
+	clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
+	set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
+	set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
+
+	mddev->sync_thread = md_register_thread(md_do_sync, mddev,
+						"reshape");
+	if (!mddev->sync_thread) {
+		ret = -EAGAIN;
+		goto abort;
+	}
+	conf->reshape_checkpoint = jiffies;
+	md_wakeup_thread(mddev->sync_thread);
+	md_new_event(mddev);
+	return 0;
+
+abort:
+	mddev->recovery = 0;
+	spin_lock_irq(&conf->device_lock);
+	conf->geo = conf->prev;
+	mddev->raid_disks = conf->geo.raid_disks;
+	rdev_for_each(rdev, mddev)
+		rdev->new_data_offset = rdev->data_offset;
+	smp_wmb();
+	conf->reshape_progress = MaxSector;
+	mddev->reshape_position = MaxSector;
+	spin_unlock_irq(&conf->device_lock);
+	return ret;
+}
+
+/* Calculate the last device-address that could contain
+ * any block from the chunk that includes the array-address 's'
+ * and report the next address.
+ * i.e. the address returned will be chunk-aligned and after
+ * any data that is in the chunk containing 's'.
+ */
+static sector_t last_dev_address(sector_t s, struct geom *geo)
+{
+	s = (s | geo->chunk_mask) + 1;
+	s >>= geo->chunk_shift;
+	s *= geo->near_copies;
+	s = DIV_ROUND_UP_SECTOR_T(s, geo->raid_disks);
+	s *= geo->far_copies;
+	s <<= geo->chunk_shift;
+	return s;
+}
+
+/* Calculate the first device-address that could contain
+ * any block from the chunk that includes the array-address 's'.
+ * This too will be the start of a chunk
+ */
+static sector_t first_dev_address(sector_t s, struct geom *geo)
+{
+	s >>= geo->chunk_shift;
+	s *= geo->near_copies;
+	sector_div(s, geo->raid_disks);
+	s *= geo->far_copies;
+	s <<= geo->chunk_shift;
+	return s;
+}
+
+static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
+				int *skipped)
+{
+	/* We simply copy at most one chunk (smallest of old and new)
+	 * at a time, possibly less if that exceeds RESYNC_PAGES,
+	 * or we hit a bad block or something.
+	 * This might mean we pause for normal IO in the middle of
+	 * a chunk, but that is not a problem was mddev->reshape_position
+	 * can record any location.
+	 *
+	 * If we will want to write to a location that isn't
+	 * yet recorded as 'safe' (i.e. in metadata on disk) then
+	 * we need to flush all reshape requests and update the metadata.
+	 *
+	 * When reshaping forwards (e.g. to more devices), we interpret
+	 * 'safe' as the earliest block which might not have been copied
+	 * down yet.  We divide this by previous stripe size and multiply
+	 * by previous stripe length to get lowest device offset that we
+	 * cannot write to yet.
+	 * We interpret 'sector_nr' as an address that we want to write to.
+	 * From this we use last_device_address() to find where we might
+	 * write to, and first_device_address on the  'safe' position.
+	 * If this 'next' write position is after the 'safe' position,
+	 * we must update the metadata to increase the 'safe' position.
+	 *
+	 * When reshaping backwards, we round in the opposite direction
+	 * and perform the reverse test:  next write position must not be
+	 * less than current safe position.
+	 *
+	 * In all this the minimum difference in data offsets
+	 * (conf->offset_diff - always positive) allows a bit of slack,
+	 * so next can be after 'safe', but not by more than offset_disk
+	 *
+	 * We need to prepare all the bios here before we start any IO
+	 * to ensure the size we choose is acceptable to all devices.
+	 * The means one for each copy for write-out and an extra one for
+	 * read-in.
+	 * We store the read-in bio in ->master_bio and the others in
+	 * ->devs[x].bio and ->devs[x].repl_bio.
+	 */
+	struct r10conf *conf = mddev->private;
+	struct r10bio *r10_bio;
+	sector_t next, safe, last;
+	int max_sectors;
+	int nr_sectors;
+	int s;
+	struct md_rdev *rdev;
+	int need_flush = 0;
+	struct bio *blist;
+	struct bio *bio, *read_bio;
+	int sectors_done = 0;
+
+	if (sector_nr == 0) {
+		/* If restarting in the middle, skip the initial sectors */
+		if (mddev->reshape_backwards &&
+		    conf->reshape_progress < raid10_size(mddev, 0, 0)) {
+			sector_nr = (raid10_size(mddev, 0, 0)
+				     - conf->reshape_progress);
+		} else if (!mddev->reshape_backwards &&
+			   conf->reshape_progress > 0)
+			sector_nr = conf->reshape_progress;
+		if (sector_nr) {
+			mddev->curr_resync_completed = sector_nr;
+			sysfs_notify(&mddev->kobj, NULL, "sync_completed");
+			*skipped = 1;
+			return sector_nr;
+		}
+	}
+
+	/* We don't use sector_nr to track where we are up to
+	 * as that doesn't work well for ->reshape_backwards.
+	 * So just use ->reshape_progress.
+	 */
+	if (mddev->reshape_backwards) {
+		/* 'next' is the earliest device address that we might
+		 * write to for this chunk in the new layout
+		 */
+		next = first_dev_address(conf->reshape_progress - 1,
+					 &conf->geo);
+
+		/* 'safe' is the last device address that we might read from
+		 * in the old layout after a restart
+		 */
+		safe = last_dev_address(conf->reshape_safe - 1,
+					&conf->prev);
+
+		if (next + conf->offset_diff < safe)
+			need_flush = 1;
+
+		last = conf->reshape_progress - 1;
+		sector_nr = last & ~(sector_t)(conf->geo.chunk_mask
+					       & conf->prev.chunk_mask);
+		if (sector_nr + RESYNC_BLOCK_SIZE/512 < last)
+			sector_nr = last + 1 - RESYNC_BLOCK_SIZE/512;
+	} else {
+		/* 'next' is after the last device address that we
+		 * might write to for this chunk in the new layout
+		 */
+		next = last_dev_address(conf->reshape_progress, &conf->geo);
+
+		/* 'safe' is the earliest device address that we might
+		 * read from in the old layout after a restart
+		 */
+		safe = first_dev_address(conf->reshape_safe, &conf->prev);
+
+		/* Need to update metadata if 'next' might be beyond 'safe'
+		 * as that would possibly corrupt data
+		 */
+		if (next > safe + conf->offset_diff)
+			need_flush = 1;
+
+		sector_nr = conf->reshape_progress;
+		last  = sector_nr | (conf->geo.chunk_mask
+				     & conf->prev.chunk_mask);
+
+		if (sector_nr + RESYNC_BLOCK_SIZE/512 <= last)
+			last = sector_nr + RESYNC_BLOCK_SIZE/512 - 1;
+	}
+
+	if (need_flush ||
+	    time_after(jiffies, conf->reshape_checkpoint + 10*HZ)) {
+		/* Need to update reshape_position in metadata */
+		wait_barrier(conf);
+		mddev->reshape_position = conf->reshape_progress;
+		if (mddev->reshape_backwards)
+			mddev->curr_resync_completed = raid10_size(mddev, 0, 0)
+				- conf->reshape_progress;
+		else
+			mddev->curr_resync_completed = conf->reshape_progress;
+		conf->reshape_checkpoint = jiffies;
+		set_bit(MD_CHANGE_DEVS, &mddev->flags);
+		md_wakeup_thread(mddev->thread);
+		wait_event(mddev->sb_wait, mddev->flags == 0 ||
+			   kthread_should_stop());
+		conf->reshape_safe = mddev->reshape_position;
+		allow_barrier(conf);
+	}
+
+read_more:
+	/* Now schedule reads for blocks from sector_nr to last */
+	r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);
+	raise_barrier(conf, sectors_done != 0);
+	atomic_set(&r10_bio->remaining, 0);
+	r10_bio->mddev = mddev;
+	r10_bio->sector = sector_nr;
+	set_bit(R10BIO_IsReshape, &r10_bio->state);
+	r10_bio->sectors = last - sector_nr + 1;
+	rdev = read_balance(conf, r10_bio, &max_sectors);
+	BUG_ON(!test_bit(R10BIO_Previous, &r10_bio->state));
+
+	if (!rdev) {
+		/* Cannot read from here, so need to record bad blocks
+		 * on all the target devices.
+		 */
+		// FIXME
+		set_bit(MD_RECOVERY_INTR, &mddev->recovery);
+		return sectors_done;
+	}
+
+	read_bio = bio_alloc_mddev(GFP_KERNEL, RESYNC_PAGES, mddev);
+
+	read_bio->bi_bdev = rdev->bdev;
+	read_bio->bi_sector = (r10_bio->devs[r10_bio->read_slot].addr
+			       + rdev->data_offset);
+	read_bio->bi_private = r10_bio;
+	read_bio->bi_end_io = end_sync_read;
+	read_bio->bi_rw = READ;
+	read_bio->bi_flags &= ~(BIO_POOL_MASK - 1);
+	read_bio->bi_flags |= 1 << BIO_UPTODATE;
+	read_bio->bi_vcnt = 0;
+	read_bio->bi_idx = 0;
+	read_bio->bi_size = 0;
+	r10_bio->master_bio = read_bio;
+	r10_bio->read_slot = r10_bio->devs[r10_bio->read_slot].devnum;
+
+	/* Now find the locations in the new layout */
+	__raid10_find_phys(&conf->geo, r10_bio);
+
+	blist = read_bio;
+	read_bio->bi_next = NULL;
+
+	for (s = 0; s < conf->copies*2; s++) {
+		struct bio *b;
+		int d = r10_bio->devs[s/2].devnum;
+		struct md_rdev *rdev2;
+		if (s&1) {
+			rdev2 = conf->mirrors[d].replacement;
+			b = r10_bio->devs[s/2].repl_bio;
+		} else {
+			rdev2 = conf->mirrors[d].rdev;
+			b = r10_bio->devs[s/2].bio;
+		}
+		if (!rdev2 || test_bit(Faulty, &rdev2->flags))
+			continue;
+		b->bi_bdev = rdev2->bdev;
+		b->bi_sector = r10_bio->devs[s/2].addr + rdev2->new_data_offset;
+		b->bi_private = r10_bio;
+		b->bi_end_io = end_reshape_write;
+		b->bi_rw = WRITE;
+		b->bi_flags &= ~(BIO_POOL_MASK - 1);
+		b->bi_flags |= 1 << BIO_UPTODATE;
+		b->bi_next = blist;
+		b->bi_vcnt = 0;
+		b->bi_idx = 0;
+		b->bi_size = 0;
+		blist = b;
+	}
+
+	/* Now add as many pages as possible to all of these bios. */
+
+	nr_sectors = 0;
+	for (s = 0 ; s < max_sectors; s += PAGE_SIZE >> 9) {
+		struct page *page = r10_bio->devs[0].bio->bi_io_vec[s/(PAGE_SIZE>>9)].bv_page;
+		int len = (max_sectors - s) << 9;
+		if (len > PAGE_SIZE)
+			len = PAGE_SIZE;
+		for (bio = blist; bio ; bio = bio->bi_next) {
+			struct bio *bio2;
+			if (bio_add_page(bio, page, len, 0))
+				continue;
+
+			/* Didn't fit, must stop */
+			for (bio2 = blist;
+			     bio2 && bio2 != bio;
+			     bio2 = bio2->bi_next) {
+				/* Remove last page from this bio */
+				bio2->bi_vcnt--;
+				bio2->bi_size -= len;
+				bio2->bi_flags &= ~(1<<BIO_SEG_VALID);
+			}
+			goto bio_full;
+		}
+		sector_nr += len >> 9;
+		nr_sectors += len >> 9;
+	}
+bio_full:
+	r10_bio->sectors = nr_sectors;
+
+	/* Now submit the read */
+	md_sync_acct(read_bio->bi_bdev, r10_bio->sectors);
+	atomic_inc(&r10_bio->remaining);
+	read_bio->bi_next = NULL;
+	generic_make_request(read_bio);
+	sector_nr += nr_sectors;
+	sectors_done += nr_sectors;
+	if (sector_nr <= last)
+		goto read_more;
+
+	/* Now that we have done the whole section we can
+	 * update reshape_progress
+	 */
+	if (mddev->reshape_backwards)
+		conf->reshape_progress -= sectors_done;
+	else
+		conf->reshape_progress += sectors_done;
+
+	return sectors_done;
+}
+
+static void end_reshape_request(struct r10bio *r10_bio);
+static int handle_reshape_read_error(struct mddev *mddev,
+				     struct r10bio *r10_bio);
+static void reshape_request_write(struct mddev *mddev, struct r10bio *r10_bio)
+{
+	/* Reshape read completed.  Hopefully we have a block
+	 * to write out.
+	 * If we got a read error then we do sync 1-page reads from
+	 * elsewhere until we find the data - or give up.
+	 */
+	struct r10conf *conf = mddev->private;
+	int s;
+
+	if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
+		if (handle_reshape_read_error(mddev, r10_bio) < 0) {
+			/* Reshape has been aborted */
+			md_done_sync(mddev, r10_bio->sectors, 0);
+			return;
+		}
+
+	/* We definitely have the data in the pages, schedule the
+	 * writes.
+	 */
+	atomic_set(&r10_bio->remaining, 1);
+	for (s = 0; s < conf->copies*2; s++) {
+		struct bio *b;
+		int d = r10_bio->devs[s/2].devnum;
+		struct md_rdev *rdev;
+		if (s&1) {
+			rdev = conf->mirrors[d].replacement;
+			b = r10_bio->devs[s/2].repl_bio;
+		} else {
+			rdev = conf->mirrors[d].rdev;
+			b = r10_bio->devs[s/2].bio;
+		}
+		if (!rdev || test_bit(Faulty, &rdev->flags))
+			continue;
+		atomic_inc(&rdev->nr_pending);
+		md_sync_acct(b->bi_bdev, r10_bio->sectors);
+		atomic_inc(&r10_bio->remaining);
+		b->bi_next = NULL;
+		generic_make_request(b);
+	}
+	end_reshape_request(r10_bio);
+}
+
+static void end_reshape(struct r10conf *conf)
+{
+	if (test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery))
+		return;
+
+	spin_lock_irq(&conf->device_lock);
+	conf->prev = conf->geo;
+	md_finish_reshape(conf->mddev);
+	smp_wmb();
+	conf->reshape_progress = MaxSector;
+	spin_unlock_irq(&conf->device_lock);
+
+	/* read-ahead size must cover two whole stripes, which is
+	 * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
+	 */
+	if (conf->mddev->queue) {
+		int stripe = conf->geo.raid_disks *
+			((conf->mddev->chunk_sectors << 9) / PAGE_SIZE);
+		stripe /= conf->geo.near_copies;
+		if (conf->mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
+			conf->mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
+	}
+	conf->fullsync = 0;
+}
+
+
+static int handle_reshape_read_error(struct mddev *mddev,
+				     struct r10bio *r10_bio)
+{
+	/* Use sync reads to get the blocks from somewhere else */
+	int sectors = r10_bio->sectors;
+	struct r10bio r10b;
+	struct r10conf *conf = mddev->private;
+	int slot = 0;
+	int idx = 0;
+	struct bio_vec *bvec = r10_bio->master_bio->bi_io_vec;
+
+	r10b.sector = r10_bio->sector;
+	__raid10_find_phys(&conf->prev, &r10b);
+
+	while (sectors) {
+		int s = sectors;
+		int success = 0;
+		int first_slot = slot;
+
+		if (s > (PAGE_SIZE >> 9))
+			s = PAGE_SIZE >> 9;
+
+		while (!success) {
+			int d = r10b.devs[slot].devnum;
+			struct md_rdev *rdev = conf->mirrors[d].rdev;
+			sector_t addr;
+			if (rdev == NULL ||
+			    test_bit(Faulty, &rdev->flags) ||
+			    !test_bit(In_sync, &rdev->flags))
+				goto failed;
+
+			addr = r10b.devs[slot].addr + idx * PAGE_SIZE;
+			success = sync_page_io(rdev,
+					       addr,
+					       s << 9,
+					       bvec[idx].bv_page,
+					       READ, false);
+			if (success)
+				break;
+		failed:
+			slot++;
+			if (slot >= conf->copies)
+				slot = 0;
+			if (slot == first_slot)
+				break;
+		}
+		if (!success) {
+			/* couldn't read this block, must give up */
+			set_bit(MD_RECOVERY_INTR,
+				&mddev->recovery);
+			return -EIO;
+		}
+		sectors -= s;
+		idx++;
+	}
+	return 0;
+}
+
+static void end_reshape_write(struct bio *bio, int error)
+{
+	int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
+	struct r10bio *r10_bio = bio->bi_private;
+	struct mddev *mddev = r10_bio->mddev;
+	struct r10conf *conf = mddev->private;
+	int d;
+	int slot;
+	int repl;
+	struct md_rdev *rdev = NULL;
+
+	d = find_bio_disk(conf, r10_bio, bio, &slot, &repl);
+	if (repl)
+		rdev = conf->mirrors[d].replacement;
+	if (!rdev) {
+		smp_mb();
+		rdev = conf->mirrors[d].rdev;
+	}
+
+	if (!uptodate) {
+		/* FIXME should record badblock */
+		md_error(mddev, rdev);
+	}
+
+	rdev_dec_pending(rdev, mddev);
+	end_reshape_request(r10_bio);
+}
+
+static void end_reshape_request(struct r10bio *r10_bio)
+{
+	if (!atomic_dec_and_test(&r10_bio->remaining))
+		return;
+	md_done_sync(r10_bio->mddev, r10_bio->sectors, 1);
+	bio_put(r10_bio->master_bio);
+	put_buf(r10_bio);
+}
+
+static void raid10_finish_reshape(struct mddev *mddev)
+{
+	struct r10conf *conf = mddev->private;
+
+	if (test_bit(MD_RECOVERY_INTR, &mddev->recovery))
+		return;
+
+	if (mddev->delta_disks > 0) {
+		sector_t size = raid10_size(mddev, 0, 0);
+		md_set_array_sectors(mddev, size);
+		if (mddev->recovery_cp > mddev->resync_max_sectors) {
+			mddev->recovery_cp = mddev->resync_max_sectors;
+			set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+		}
+		mddev->resync_max_sectors = size;
+		set_capacity(mddev->gendisk, mddev->array_sectors);
+		revalidate_disk(mddev->gendisk);
+	} else {
+		int d;
+		for (d = conf->geo.raid_disks ;
+		     d < conf->geo.raid_disks - mddev->delta_disks;
+		     d++) {
+			struct md_rdev *rdev = conf->mirrors[d].rdev;
+			if (rdev)
+				clear_bit(In_sync, &rdev->flags);
+			rdev = conf->mirrors[d].replacement;
+			if (rdev)
+				clear_bit(In_sync, &rdev->flags);
+		}
+	}
+	mddev->layout = mddev->new_layout;
+	mddev->chunk_sectors = 1 << conf->geo.chunk_shift;
+	mddev->reshape_position = MaxSector;
+	mddev->delta_disks = 0;
+	mddev->reshape_backwards = 0;
+}
+
 static struct md_personality raid10_personality =
 {
 	.name		= "raid10",
@@ -3552,6 +4524,9 @@ static struct md_personality raid10_personality =
 	.size		= raid10_size,
 	.resize		= raid10_resize,
 	.takeover	= raid10_takeover,
+	.check_reshape	= raid10_check_reshape,
+	.start_reshape	= raid10_start_reshape,
+	.finish_reshape	= raid10_finish_reshape,
 };
 
 static int __init raid_init(void)
diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h
index 7c615613c38..135b1b0a155 100644
--- a/drivers/md/raid10.h
+++ b/drivers/md/raid10.h
@@ -14,32 +14,38 @@ struct mirror_info {
 struct r10conf {
 	struct mddev		*mddev;
 	struct mirror_info	*mirrors;
-	int			raid_disks;
+	struct mirror_info	*mirrors_new, *mirrors_old;
 	spinlock_t		device_lock;
 
 	/* geometry */
-	int			near_copies;  /* number of copies laid out
+	struct geom {
+		int		raid_disks;
+		int		near_copies;  /* number of copies laid out
 					       * raid0 style */
-	int 			far_copies;   /* number of copies laid out
+		int		far_copies;   /* number of copies laid out
 					       * at large strides across drives
 					       */
-	int			far_offset;   /* far_copies are offset by 1
+		int		far_offset;   /* far_copies are offset by 1
 					       * stripe instead of many
 					       */
-	int			copies;	      /* near_copies * far_copies.
-					       * must be <= raid_disks
-					       */
-	sector_t		stride;	      /* distance between far copies.
+		sector_t	stride;	      /* distance between far copies.
 					       * This is size / far_copies unless
 					       * far_offset, in which case it is
 					       * 1 stripe.
 					       */
+		int		chunk_shift; /* shift from chunks to sectors */
+		sector_t	chunk_mask;
+	} prev, geo;
+	int			copies;	      /* near_copies * far_copies.
+					       * must be <= raid_disks
+					       */
 
 	sector_t		dev_sectors;  /* temp copy of
 					       * mddev->dev_sectors */
-
-	int			chunk_shift; /* shift from chunks to sectors */
-	sector_t		chunk_mask;
+	sector_t		reshape_progress;
+	sector_t		reshape_safe;
+	unsigned long		reshape_checkpoint;
+	sector_t		offset_diff;
 
 	struct list_head	retry_list;
 	/* queue pending writes and submit them on unplug */
@@ -136,6 +142,7 @@ enum r10bio_state {
 	R10BIO_Uptodate,
 	R10BIO_IsSync,
 	R10BIO_IsRecover,
+	R10BIO_IsReshape,
 	R10BIO_Degraded,
 /* Set ReadError on bios that experience a read error
  * so that raid10d knows what to do with them.
@@ -146,5 +153,10 @@ enum r10bio_state {
  */
 	R10BIO_MadeGood,
 	R10BIO_WriteError,
+/* During a reshape we might be performing IO on the
+ * 'previous' part of the array, in which case this
+ * flag is set
+ */
+	R10BIO_Previous,
 };
 #endif
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index f351422938e..d26767246d2 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -488,6 +488,27 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
 	return sh;
 }
 
+/* Determine if 'data_offset' or 'new_data_offset' should be used
+ * in this stripe_head.
+ */
+static int use_new_offset(struct r5conf *conf, struct stripe_head *sh)
+{
+	sector_t progress = conf->reshape_progress;
+	/* Need a memory barrier to make sure we see the value
+	 * of conf->generation, or ->data_offset that was set before
+	 * reshape_progress was updated.
+	 */
+	smp_rmb();
+	if (progress == MaxSector)
+		return 0;
+	if (sh->generation == conf->generation - 1)
+		return 0;
+	/* We are in a reshape, and this is a new-generation stripe,
+	 * so use new_data_offset.
+	 */
+	return 1;
+}
+
 static void
 raid5_end_read_request(struct bio *bi, int error);
 static void
@@ -518,6 +539,8 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
 			replace_only = 1;
 		} else
 			continue;
+		if (test_and_clear_bit(R5_SyncIO, &sh->dev[i].flags))
+			rw |= REQ_SYNC;
 
 		bi = &sh->dev[i].req;
 		rbi = &sh->dev[i].rreq; /* For writing to replacement */
@@ -603,7 +626,12 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
 				__func__, (unsigned long long)sh->sector,
 				bi->bi_rw, i);
 			atomic_inc(&sh->count);
-			bi->bi_sector = sh->sector + rdev->data_offset;
+			if (use_new_offset(conf, sh))
+				bi->bi_sector = (sh->sector
+						 + rdev->new_data_offset);
+			else
+				bi->bi_sector = (sh->sector
+						 + rdev->data_offset);
 			bi->bi_flags = 1 << BIO_UPTODATE;
 			bi->bi_idx = 0;
 			bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
@@ -627,7 +655,12 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
 				__func__, (unsigned long long)sh->sector,
 				rbi->bi_rw, i);
 			atomic_inc(&sh->count);
-			rbi->bi_sector = sh->sector + rrdev->data_offset;
+			if (use_new_offset(conf, sh))
+				rbi->bi_sector = (sh->sector
+						  + rrdev->new_data_offset);
+			else
+				rbi->bi_sector = (sh->sector
+						  + rrdev->data_offset);
 			rbi->bi_flags = 1 << BIO_UPTODATE;
 			rbi->bi_idx = 0;
 			rbi->bi_io_vec[0].bv_len = STRIPE_SIZE;
@@ -1114,6 +1147,8 @@ ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
 				dev->sector + STRIPE_SECTORS) {
 				if (wbi->bi_rw & REQ_FUA)
 					set_bit(R5_WantFUA, &dev->flags);
+				if (wbi->bi_rw & REQ_SYNC)
+					set_bit(R5_SyncIO, &dev->flags);
 				tx = async_copy_data(1, wbi, dev->page,
 					dev->sector, tx);
 				wbi = r5_next_bio(wbi, dev->sector);
@@ -1131,13 +1166,15 @@ static void ops_complete_reconstruct(void *stripe_head_ref)
 	int pd_idx = sh->pd_idx;
 	int qd_idx = sh->qd_idx;
 	int i;
-	bool fua = false;
+	bool fua = false, sync = false;
 
 	pr_debug("%s: stripe %llu\n", __func__,
 		(unsigned long long)sh->sector);
 
-	for (i = disks; i--; )
+	for (i = disks; i--; ) {
 		fua |= test_bit(R5_WantFUA, &sh->dev[i].flags);
+		sync |= test_bit(R5_SyncIO, &sh->dev[i].flags);
+	}
 
 	for (i = disks; i--; ) {
 		struct r5dev *dev = &sh->dev[i];
@@ -1146,6 +1183,8 @@ static void ops_complete_reconstruct(void *stripe_head_ref)
 			set_bit(R5_UPTODATE, &dev->flags);
 			if (fua)
 				set_bit(R5_WantFUA, &dev->flags);
+			if (sync)
+				set_bit(R5_SyncIO, &dev->flags);
 		}
 	}
 
@@ -1648,7 +1687,7 @@ static void raid5_end_read_request(struct bio * bi, int error)
 	int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
 	char b[BDEVNAME_SIZE];
 	struct md_rdev *rdev = NULL;
-
+	sector_t s;
 
 	for (i=0 ; i<disks; i++)
 		if (bi == &sh->dev[i].req)
@@ -1671,6 +1710,10 @@ static void raid5_end_read_request(struct bio * bi, int error)
 	if (!rdev)
 		rdev = conf->disks[i].rdev;
 
+	if (use_new_offset(conf, sh))
+		s = sh->sector + rdev->new_data_offset;
+	else
+		s = sh->sector + rdev->data_offset;
 	if (uptodate) {
 		set_bit(R5_UPTODATE, &sh->dev[i].flags);
 		if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
@@ -1683,8 +1726,7 @@ static void raid5_end_read_request(struct bio * bi, int error)
 				"md/raid:%s: read error corrected"
 				" (%lu sectors at %llu on %s)\n",
 				mdname(conf->mddev), STRIPE_SECTORS,
-				(unsigned long long)(sh->sector
-						     + rdev->data_offset),
+				(unsigned long long)s,
 				bdevname(rdev->bdev, b));
 			atomic_add(STRIPE_SECTORS, &rdev->corrected_errors);
 			clear_bit(R5_ReadError, &sh->dev[i].flags);
@@ -1704,8 +1746,7 @@ static void raid5_end_read_request(struct bio * bi, int error)
 				"md/raid:%s: read error on replacement device "
 				"(sector %llu on %s).\n",
 				mdname(conf->mddev),
-				(unsigned long long)(sh->sector
-						     + rdev->data_offset),
+				(unsigned long long)s,
 				bdn);
 		else if (conf->mddev->degraded >= conf->max_degraded)
 			printk_ratelimited(
@@ -1713,8 +1754,7 @@ static void raid5_end_read_request(struct bio * bi, int error)
 				"md/raid:%s: read error not correctable "
 				"(sector %llu on %s).\n",
 				mdname(conf->mddev),
-				(unsigned long long)(sh->sector
-						     + rdev->data_offset),
+				(unsigned long long)s,
 				bdn);
 		else if (test_bit(R5_ReWrite, &sh->dev[i].flags))
 			/* Oh, no!!! */
@@ -1723,8 +1763,7 @@ static void raid5_end_read_request(struct bio * bi, int error)
 				"md/raid:%s: read error NOT corrected!! "
 				"(sector %llu on %s).\n",
 				mdname(conf->mddev),
-				(unsigned long long)(sh->sector
-						     + rdev->data_offset),
+				(unsigned long long)s,
 				bdn);
 		else if (atomic_read(&rdev->read_errors)
 			 > conf->max_nr_stripes)
@@ -3561,7 +3600,7 @@ finish:
 			if (test_and_clear_bit(R5_MadeGood, &dev->flags)) {
 				rdev = conf->disks[i].rdev;
 				rdev_clear_badblocks(rdev, sh->sector,
-						     STRIPE_SECTORS);
+						     STRIPE_SECTORS, 0);
 				rdev_dec_pending(rdev, conf->mddev);
 			}
 			if (test_and_clear_bit(R5_MadeGoodRepl, &dev->flags)) {
@@ -3570,7 +3609,7 @@ finish:
 					/* rdev have been moved down */
 					rdev = conf->disks[i].rdev;
 				rdev_clear_badblocks(rdev, sh->sector,
-						     STRIPE_SECTORS);
+						     STRIPE_SECTORS, 0);
 				rdev_dec_pending(rdev, conf->mddev);
 			}
 		}
@@ -3842,6 +3881,7 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
 		raid_bio->bi_next = (void*)rdev;
 		align_bi->bi_bdev =  rdev->bdev;
 		align_bi->bi_flags &= ~(1 << BIO_SEG_VALID);
+		/* No reshape active, so we can trust rdev->data_offset */
 		align_bi->bi_sector += rdev->data_offset;
 
 		if (!bio_fits_rdev(align_bi) ||
@@ -3953,12 +3993,10 @@ static void make_request(struct mddev *mddev, struct bio * bi)
 	plugged = mddev_check_plugged(mddev);
 	for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
 		DEFINE_WAIT(w);
-		int disks, data_disks;
 		int previous;
 
 	retry:
 		previous = 0;
-		disks = conf->raid_disks;
 		prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
 		if (unlikely(conf->reshape_progress != MaxSector)) {
 			/* spinlock is needed as reshape_progress may be
@@ -3970,13 +4008,12 @@ static void make_request(struct mddev *mddev, struct bio * bi)
 			 * to check again.
 			 */
 			spin_lock_irq(&conf->device_lock);
-			if (mddev->delta_disks < 0
+			if (mddev->reshape_backwards
 			    ? logical_sector < conf->reshape_progress
 			    : logical_sector >= conf->reshape_progress) {
-				disks = conf->previous_raid_disks;
 				previous = 1;
 			} else {
-				if (mddev->delta_disks < 0
+				if (mddev->reshape_backwards
 				    ? logical_sector < conf->reshape_safe
 				    : logical_sector >= conf->reshape_safe) {
 					spin_unlock_irq(&conf->device_lock);
@@ -3986,7 +4023,6 @@ static void make_request(struct mddev *mddev, struct bio * bi)
 			}
 			spin_unlock_irq(&conf->device_lock);
 		}
-		data_disks = disks - conf->max_degraded;
 
 		new_sector = raid5_compute_sector(conf, logical_sector,
 						  previous,
@@ -4009,7 +4045,7 @@ static void make_request(struct mddev *mddev, struct bio * bi)
 				 */
 				int must_retry = 0;
 				spin_lock_irq(&conf->device_lock);
-				if (mddev->delta_disks < 0
+				if (mddev->reshape_backwards
 				    ? logical_sector >= conf->reshape_progress
 				    : logical_sector < conf->reshape_progress)
 					/* mismatch, need to try again */
@@ -4108,11 +4144,11 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr, int *sk
 
 	if (sector_nr == 0) {
 		/* If restarting in the middle, skip the initial sectors */
-		if (mddev->delta_disks < 0 &&
+		if (mddev->reshape_backwards &&
 		    conf->reshape_progress < raid5_size(mddev, 0, 0)) {
 			sector_nr = raid5_size(mddev, 0, 0)
 				- conf->reshape_progress;
-		} else if (mddev->delta_disks >= 0 &&
+		} else if (!mddev->reshape_backwards &&
 			   conf->reshape_progress > 0)
 			sector_nr = conf->reshape_progress;
 		sector_div(sector_nr, new_data_disks);
@@ -4133,13 +4169,11 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr, int *sk
 	else
 		reshape_sectors = mddev->chunk_sectors;
 
-	/* we update the metadata when there is more than 3Meg
-	 * in the block range (that is rather arbitrary, should
-	 * probably be time based) or when the data about to be
-	 * copied would over-write the source of the data at
-	 * the front of the range.
-	 * i.e. one new_stripe along from reshape_progress new_maps
-	 * to after where reshape_safe old_maps to
+	/* We update the metadata at least every 10 seconds, or when
+	 * the data about to be copied would over-write the source of
+	 * the data at the front of the range.  i.e. one new_stripe
+	 * along from reshape_progress new_maps to after where
+	 * reshape_safe old_maps to
 	 */
 	writepos = conf->reshape_progress;
 	sector_div(writepos, new_data_disks);
@@ -4147,7 +4181,7 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr, int *sk
 	sector_div(readpos, data_disks);
 	safepos = conf->reshape_safe;
 	sector_div(safepos, data_disks);
-	if (mddev->delta_disks < 0) {
+	if (mddev->reshape_backwards) {
 		writepos -= min_t(sector_t, reshape_sectors, writepos);
 		readpos += reshape_sectors;
 		safepos += reshape_sectors;
@@ -4157,11 +4191,29 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr, int *sk
 		safepos -= min_t(sector_t, reshape_sectors, safepos);
 	}
 
+	/* Having calculated the 'writepos' possibly use it
+	 * to set 'stripe_addr' which is where we will write to.
+	 */
+	if (mddev->reshape_backwards) {
+		BUG_ON(conf->reshape_progress == 0);
+		stripe_addr = writepos;
+		BUG_ON((mddev->dev_sectors &
+			~((sector_t)reshape_sectors - 1))
+		       - reshape_sectors - stripe_addr
+		       != sector_nr);
+	} else {
+		BUG_ON(writepos != sector_nr + reshape_sectors);
+		stripe_addr = sector_nr;
+	}
+
 	/* 'writepos' is the most advanced device address we might write.
 	 * 'readpos' is the least advanced device address we might read.
 	 * 'safepos' is the least address recorded in the metadata as having
 	 *     been reshaped.
-	 * If 'readpos' is behind 'writepos', then there is no way that we can
+	 * If there is a min_offset_diff, these are adjusted either by
+	 * increasing the safepos/readpos if diff is negative, or
+	 * increasing writepos if diff is positive.
+	 * If 'readpos' is then behind 'writepos', there is no way that we can
 	 * ensure safety in the face of a crash - that must be done by userspace
 	 * making a backup of the data.  So in that case there is no particular
 	 * rush to update metadata.
@@ -4174,7 +4226,13 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr, int *sk
 	 * Maybe that number should be configurable, but I'm not sure it is
 	 * worth it.... maybe it could be a multiple of safemode_delay???
 	 */
-	if ((mddev->delta_disks < 0
+	if (conf->min_offset_diff < 0) {
+		safepos += -conf->min_offset_diff;
+		readpos += -conf->min_offset_diff;
+	} else
+		writepos += conf->min_offset_diff;
+
+	if ((mddev->reshape_backwards
 	     ? (safepos > writepos && readpos < writepos)
 	     : (safepos < writepos && readpos > writepos)) ||
 	    time_after(jiffies, conf->reshape_checkpoint + 10*HZ)) {
@@ -4195,17 +4253,6 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr, int *sk
 		sysfs_notify(&mddev->kobj, NULL, "sync_completed");
 	}
 
-	if (mddev->delta_disks < 0) {
-		BUG_ON(conf->reshape_progress == 0);
-		stripe_addr = writepos;
-		BUG_ON((mddev->dev_sectors &
-			~((sector_t)reshape_sectors - 1))
-		       - reshape_sectors - stripe_addr
-		       != sector_nr);
-	} else {
-		BUG_ON(writepos != sector_nr + reshape_sectors);
-		stripe_addr = sector_nr;
-	}
 	INIT_LIST_HEAD(&stripes);
 	for (i = 0; i < reshape_sectors; i += STRIPE_SECTORS) {
 		int j;
@@ -4239,7 +4286,7 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr, int *sk
 		list_add(&sh->lru, &stripes);
 	}
 	spin_lock_irq(&conf->device_lock);
-	if (mddev->delta_disks < 0)
+	if (mddev->reshape_backwards)
 		conf->reshape_progress -= reshape_sectors * new_data_disks;
 	else
 		conf->reshape_progress += reshape_sectors * new_data_disks;
@@ -4952,16 +4999,42 @@ static int run(struct mddev *mddev)
 	struct md_rdev *rdev;
 	sector_t reshape_offset = 0;
 	int i;
+	long long min_offset_diff = 0;
+	int first = 1;
 
 	if (mddev->recovery_cp != MaxSector)
 		printk(KERN_NOTICE "md/raid:%s: not clean"
 		       " -- starting background reconstruction\n",
 		       mdname(mddev));
+
+	rdev_for_each(rdev, mddev) {
+		long long diff;
+		if (rdev->raid_disk < 0)
+			continue;
+		diff = (rdev->new_data_offset - rdev->data_offset);
+		if (first) {
+			min_offset_diff = diff;
+			first = 0;
+		} else if (mddev->reshape_backwards &&
+			 diff < min_offset_diff)
+			min_offset_diff = diff;
+		else if (!mddev->reshape_backwards &&
+			 diff > min_offset_diff)
+			min_offset_diff = diff;
+	}
+
 	if (mddev->reshape_position != MaxSector) {
 		/* Check that we can continue the reshape.
-		 * Currently only disks can change, it must
-		 * increase, and we must be past the point where
-		 * a stripe over-writes itself
+		 * Difficulties arise if the stripe we would write to
+		 * next is at or after the stripe we would read from next.
+		 * For a reshape that changes the number of devices, this
+		 * is only possible for a very short time, and mdadm makes
+		 * sure that time appears to have past before assembling
+		 * the array.  So we fail if that time hasn't passed.
+		 * For a reshape that keeps the number of devices the same
+		 * mdadm must be monitoring the reshape can keeping the
+		 * critical areas read-only and backed up.  It will start
+		 * the array in read-only mode, so we check for that.
 		 */
 		sector_t here_new, here_old;
 		int old_disks;
@@ -4993,26 +5066,34 @@ static int run(struct mddev *mddev)
 		/* here_old is the first stripe that we might need to read
 		 * from */
 		if (mddev->delta_disks == 0) {
+			if ((here_new * mddev->new_chunk_sectors !=
+			     here_old * mddev->chunk_sectors)) {
+				printk(KERN_ERR "md/raid:%s: reshape position is"
+				       " confused - aborting\n", mdname(mddev));
+				return -EINVAL;
+			}
 			/* We cannot be sure it is safe to start an in-place
-			 * reshape.  It is only safe if user-space if monitoring
+			 * reshape.  It is only safe if user-space is monitoring
 			 * and taking constant backups.
 			 * mdadm always starts a situation like this in
 			 * readonly mode so it can take control before
 			 * allowing any writes.  So just check for that.
 			 */
-			if ((here_new * mddev->new_chunk_sectors != 
-			     here_old * mddev->chunk_sectors) ||
-			    mddev->ro == 0) {
-				printk(KERN_ERR "md/raid:%s: in-place reshape must be started"
-				       " in read-only mode - aborting\n",
+			if (abs(min_offset_diff) >= mddev->chunk_sectors &&
+			    abs(min_offset_diff) >= mddev->new_chunk_sectors)
+				/* not really in-place - so OK */;
+			else if (mddev->ro == 0) {
+				printk(KERN_ERR "md/raid:%s: in-place reshape "
+				       "must be started in read-only mode "
+				       "- aborting\n",
 				       mdname(mddev));
 				return -EINVAL;
 			}
-		} else if (mddev->delta_disks < 0
-		    ? (here_new * mddev->new_chunk_sectors <=
+		} else if (mddev->reshape_backwards
+		    ? (here_new * mddev->new_chunk_sectors + min_offset_diff <=
 		       here_old * mddev->chunk_sectors)
 		    : (here_new * mddev->new_chunk_sectors >=
-		       here_old * mddev->chunk_sectors)) {
+		       here_old * mddev->chunk_sectors + (-min_offset_diff))) {
 			/* Reading from the same stripe as writing to - bad */
 			printk(KERN_ERR "md/raid:%s: reshape_position too early for "
 			       "auto-recovery - aborting.\n",
@@ -5037,6 +5118,7 @@ static int run(struct mddev *mddev)
 	if (IS_ERR(conf))
 		return PTR_ERR(conf);
 
+	conf->min_offset_diff = min_offset_diff;
 	mddev->thread = conf->thread;
 	conf->thread = NULL;
 	mddev->private = conf;
@@ -5182,9 +5264,12 @@ static int run(struct mddev *mddev)
 		blk_queue_io_opt(mddev->queue, chunk_size *
 				 (conf->raid_disks - conf->max_degraded));
 
-		rdev_for_each(rdev, mddev)
+		rdev_for_each(rdev, mddev) {
 			disk_stack_limits(mddev->gendisk, rdev->bdev,
 					  rdev->data_offset << 9);
+			disk_stack_limits(mddev->gendisk, rdev->bdev,
+					  rdev->new_data_offset << 9);
+		}
 	}
 
 	return 0;
@@ -5418,12 +5503,18 @@ static int raid5_resize(struct mddev *mddev, sector_t sectors)
 	 * any io in the removed space completes, but it hardly seems
 	 * worth it.
 	 */
+	sector_t newsize;
 	sectors &= ~((sector_t)mddev->chunk_sectors - 1);
-	md_set_array_sectors(mddev, raid5_size(mddev, sectors,
-					       mddev->raid_disks));
-	if (mddev->array_sectors >
-	    raid5_size(mddev, sectors, mddev->raid_disks))
+	newsize = raid5_size(mddev, sectors, mddev->raid_disks);
+	if (mddev->external_size &&
+	    mddev->array_sectors > newsize)
 		return -EINVAL;
+	if (mddev->bitmap) {
+		int ret = bitmap_resize(mddev->bitmap, sectors, 0, 0);
+		if (ret)
+			return ret;
+	}
+	md_set_array_sectors(mddev, newsize);
 	set_capacity(mddev->gendisk, mddev->array_sectors);
 	revalidate_disk(mddev->gendisk);
 	if (sectors > mddev->dev_sectors &&
@@ -5468,9 +5559,6 @@ static int check_reshape(struct mddev *mddev)
 	    mddev->new_layout == mddev->layout &&
 	    mddev->new_chunk_sectors == mddev->chunk_sectors)
 		return 0; /* nothing to do */
-	if (mddev->bitmap)
-		/* Cannot grow a bitmap yet */
-		return -EBUSY;
 	if (has_failed(conf))
 		return -EINVAL;
 	if (mddev->delta_disks < 0) {
@@ -5505,10 +5593,14 @@ static int raid5_start_reshape(struct mddev *mddev)
 	if (!check_stripe_cache(mddev))
 		return -ENOSPC;
 
-	rdev_for_each(rdev, mddev)
+	if (has_failed(conf))
+		return -EINVAL;
+
+	rdev_for_each(rdev, mddev) {
 		if (!test_bit(In_sync, &rdev->flags)
 		    && !test_bit(Faulty, &rdev->flags))
 			spares++;
+	}
 
 	if (spares - mddev->degraded < mddev->delta_disks - conf->max_degraded)
 		/* Not enough devices even to make a degraded array
@@ -5535,12 +5627,16 @@ static int raid5_start_reshape(struct mddev *mddev)
 	conf->chunk_sectors = mddev->new_chunk_sectors;
 	conf->prev_algo = conf->algorithm;
 	conf->algorithm = mddev->new_layout;
-	if (mddev->delta_disks < 0)
+	conf->generation++;
+	/* Code that selects data_offset needs to see the generation update
+	 * if reshape_progress has been set - so a memory barrier needed.
+	 */
+	smp_mb();
+	if (mddev->reshape_backwards)
 		conf->reshape_progress = raid5_size(mddev, 0, 0);
 	else
 		conf->reshape_progress = 0;
 	conf->reshape_safe = conf->reshape_progress;
-	conf->generation++;
 	spin_unlock_irq(&conf->device_lock);
 
 	/* Add some new drives, as many as will fit.
@@ -5592,6 +5688,9 @@ static int raid5_start_reshape(struct mddev *mddev)
 		mddev->recovery = 0;
 		spin_lock_irq(&conf->device_lock);
 		mddev->raid_disks = conf->raid_disks = conf->previous_raid_disks;
+		rdev_for_each(rdev, mddev)
+			rdev->new_data_offset = rdev->data_offset;
+		smp_wmb();
 		conf->reshape_progress = MaxSector;
 		mddev->reshape_position = MaxSector;
 		spin_unlock_irq(&conf->device_lock);
@@ -5610,9 +5709,13 @@ static void end_reshape(struct r5conf *conf)
 {
 
 	if (!test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery)) {
+		struct md_rdev *rdev;
 
 		spin_lock_irq(&conf->device_lock);
 		conf->previous_raid_disks = conf->raid_disks;
+		rdev_for_each(rdev, conf->mddev)
+			rdev->data_offset = rdev->new_data_offset;
+		smp_wmb();
 		conf->reshape_progress = MaxSector;
 		spin_unlock_irq(&conf->device_lock);
 		wake_up(&conf->wait_for_overlap);
@@ -5652,17 +5755,18 @@ static void raid5_finish_reshape(struct mddev *mddev)
 			     d < conf->raid_disks - mddev->delta_disks;
 			     d++) {
 				struct md_rdev *rdev = conf->disks[d].rdev;
-				if (rdev &&
-				    raid5_remove_disk(mddev, rdev) == 0) {
-					sysfs_unlink_rdev(mddev, rdev);
-					rdev->raid_disk = -1;
-				}
+				if (rdev)
+					clear_bit(In_sync, &rdev->flags);
+				rdev = conf->disks[d].replacement;
+				if (rdev)
+					clear_bit(In_sync, &rdev->flags);
 			}
 		}
 		mddev->layout = conf->algorithm;
 		mddev->chunk_sectors = conf->chunk_sectors;
 		mddev->reshape_position = MaxSector;
 		mddev->delta_disks = 0;
+		mddev->reshape_backwards = 0;
 	}
 }
 
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 8d8e13934a4..2164021f3b5 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -285,6 +285,7 @@ enum r5dev_flags {
 			 */
 	R5_Wantdrain,	/* dev->towrite needs to be drained */
 	R5_WantFUA,	/* Write should be FUA */
+	R5_SyncIO,	/* The IO is sync */
 	R5_WriteError,	/* got a write error - need to record it */
 	R5_MadeGood,	/* A bad block has been fixed by writing to it */
 	R5_ReadRepl,	/* Will/did read from replacement rather than orig */
@@ -385,6 +386,12 @@ struct r5conf {
 	short			generation; /* increments with every reshape */
 	unsigned long		reshape_checkpoint; /* Time we last updated
 						     * metadata */
+	long long		min_offset_diff; /* minimum difference between
+						  * data_offset and
+						  * new_data_offset across all
+						  * devices.  May be negative,
+						  * but is closest to zero.
+						  */
 
 	struct list_head	handle_list; /* stripes needing handling */
 	struct list_head	hold_list; /* preread ready stripes */