Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs

Pull ext2, ext3 and quota fixes from Jan Kara:
 "Interesting bits are:
   - removal of a special i_mutex locking subclass (I_MUTEX_QUOTA) since
     quota code does not need i_mutex anymore in any unusual way.
   - backport (from ext4) of a fix of a checkpointing bug (missing cache
     flush) that could lead to fs corruption on power failure

  The rest are just random small fixes & cleanups."

* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs:
  ext2: trivial fix to comment for ext2_free_blocks
  ext2: remove the redundant comment for ext2_export_ops
  ext3: return 32/64-bit dir name hash according to usage type
  quota: Get rid of nested I_MUTEX_QUOTA locking subclass
  quota: Use precomputed value of sb_dqopt in dquot_quota_sync
  ext2: Remove i_mutex use from ext2_quota_write()
  reiserfs: Remove i_mutex use from reiserfs_quota_write()
  ext4: Remove i_mutex use from ext4_quota_write()
  ext3: Remove i_mutex use from ext3_quota_write()
  quota: Fix double lock in add_dquot_ref() with CONFIG_QUOTA_DEBUG
  jbd: Write journal superblock with WRITE_FUA after checkpointing
  jbd: protect all log tail updates with j_checkpoint_mutex
  jbd: Split updating of journal superblock and marking journal empty
  ext2: do not register write_super within VFS
  ext2: Remove s_dirt handling
  ext2: write superblock only once on unmount
  ext3: update documentation with barrier=1 default
  ext3: remove max_debt in find_group_orlov()
  jbd: Refine commit writeout logic

16 files changed, 313 insertions, 211 deletions

diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
index 030c6d277e1..1c361399886 100644
--- a/fs/ext2/balloc.c
+++ b/fs/ext2/balloc.c
@@ -165,7 +165,6 @@ static void release_blocks(struct super_block *sb, int count)
 		struct ext2_sb_info *sbi = EXT2_SB(sb);
 
 		percpu_counter_add(&sbi->s_freeblocks_counter, count);
-		sb->s_dirt = 1;
 	}
 }
 
@@ -180,7 +179,6 @@ static void group_adjust_blocks(struct super_block *sb, int group_no,
 		free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
 		desc->bg_free_blocks_count = cpu_to_le16(free_blocks + count);
 		spin_unlock(sb_bgl_lock(sbi, group_no));
-		sb->s_dirt = 1;
 		mark_buffer_dirty(bh);
 	}
 }
@@ -479,7 +477,7 @@ void ext2_discard_reservation(struct inode *inode)
 }
 
 /**
- * ext2_free_blocks_sb() -- Free given blocks and update quota and i_blocks
+ * ext2_free_blocks() -- Free given blocks and update quota and i_blocks
  * @inode:		inode
  * @block:		start physcial block to free
  * @count:		number of blocks to free
diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c
index 8b15cf8cef3..c13eb7b91a1 100644
--- a/fs/ext2/ialloc.c
+++ b/fs/ext2/ialloc.c
@@ -81,7 +81,6 @@ static void ext2_release_inode(struct super_block *sb, int group, int dir)
 	spin_unlock(sb_bgl_lock(EXT2_SB(sb), group));
 	if (dir)
 		percpu_counter_dec(&EXT2_SB(sb)->s_dirs_counter);
-	sb->s_dirt = 1;
 	mark_buffer_dirty(bh);
 }
 
@@ -543,7 +542,6 @@ got:
 	}
 	spin_unlock(sb_bgl_lock(sbi, group));
 
-	sb->s_dirt = 1;
 	mark_buffer_dirty(bh2);
 	if (test_opt(sb, GRPID)) {
 		inode->i_mode = mode;
diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 38f816071dd..b3621cb7ea3 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -130,9 +130,6 @@ static void ext2_put_super (struct super_block * sb)
 
 	dquot_disable(sb, -1, DQUOT_USAGE_ENABLED | DQUOT_LIMITS_ENABLED);
 
-	if (sb->s_dirt)
-		ext2_write_super(sb);
-
 	ext2_xattr_put_super(sb);
 	if (!(sb->s_flags & MS_RDONLY)) {
 		struct ext2_super_block *es = sbi->s_es;
@@ -307,7 +304,6 @@ static const struct super_operations ext2_sops = {
 	.write_inode	= ext2_write_inode,
 	.evict_inode	= ext2_evict_inode,
 	.put_super	= ext2_put_super,
-	.write_super	= ext2_write_super,
 	.sync_fs	= ext2_sync_fs,
 	.statfs		= ext2_statfs,
 	.remount_fs	= ext2_remount,
@@ -358,11 +354,6 @@ static struct dentry *ext2_fh_to_parent(struct super_block *sb, struct fid *fid,
 				    ext2_nfs_get_inode);
 }
 
-/* Yes, most of these are left as NULL!!
- * A NULL value implies the default, which works with ext2-like file
- * systems, but can be improved upon.
- * Currently only get_parent is required.
- */
 static const struct export_operations ext2_export_ops = {
 	.fh_to_dentry = ext2_fh_to_dentry,
 	.fh_to_parent = ext2_fh_to_parent,
@@ -1176,7 +1167,6 @@ static void ext2_sync_super(struct super_block *sb, struct ext2_super_block *es,
 	mark_buffer_dirty(EXT2_SB(sb)->s_sbh);
 	if (wait)
 		sync_dirty_buffer(EXT2_SB(sb)->s_sbh);
-	sb->s_dirt = 0;
 }
 
 /*
@@ -1209,8 +1199,6 @@ void ext2_write_super(struct super_block *sb)
 {
 	if (!(sb->s_flags & MS_RDONLY))
 		ext2_sync_fs(sb, 1);
-	else
-		sb->s_dirt = 0;
 }
 
 static int ext2_remount (struct super_block * sb, int * flags, char * data)
@@ -1456,7 +1444,6 @@ static ssize_t ext2_quota_write(struct super_block *sb, int type,
 	struct buffer_head tmp_bh;
 	struct buffer_head *bh;
 
-	mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
 	while (towrite > 0) {
 		tocopy = sb->s_blocksize - offset < towrite ?
 				sb->s_blocksize - offset : towrite;
@@ -1486,16 +1473,13 @@ static ssize_t ext2_quota_write(struct super_block *sb, int type,
 		blk++;
 	}
 out:
-	if (len == towrite) {
-		mutex_unlock(&inode->i_mutex);
+	if (len == towrite)
 		return err;
-	}
 	if (inode->i_size < off+len-towrite)
 		i_size_write(inode, off+len-towrite);
 	inode->i_version++;
 	inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 	mark_inode_dirty(inode);
-	mutex_unlock(&inode->i_mutex);
 	return len - towrite;
 }
 
diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
index 6dcafc7efdf..b6754dbbce3 100644
--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -339,7 +339,6 @@ static void ext2_xattr_update_super_block(struct super_block *sb)
 	spin_lock(&EXT2_SB(sb)->s_lock);
 	EXT2_SET_COMPAT_FEATURE(sb, EXT2_FEATURE_COMPAT_EXT_ATTR);
 	spin_unlock(&EXT2_SB(sb)->s_lock);
-	sb->s_dirt = 1;
 	mark_buffer_dirty(EXT2_SB(sb)->s_sbh);
 }
 
diff --git a/fs/ext3/dir.c b/fs/ext3/dir.c
index cc761ad8fa5..92490e9f85c 100644
--- a/fs/ext3/dir.c
+++ b/fs/ext3/dir.c
@@ -21,30 +21,15 @@
  *
  */
 
+#include <linux/compat.h>
 #include "ext3.h"
 
 static unsigned char ext3_filetype_table[] = {
 	DT_UNKNOWN, DT_REG, DT_DIR, DT_CHR, DT_BLK, DT_FIFO, DT_SOCK, DT_LNK
 };
 
-static int ext3_readdir(struct file *, void *, filldir_t);
 static int ext3_dx_readdir(struct file * filp,
 			   void * dirent, filldir_t filldir);
-static int ext3_release_dir (struct inode * inode,
-				struct file * filp);
-
-const struct file_operations ext3_dir_operations = {
-	.llseek		= generic_file_llseek,
-	.read		= generic_read_dir,
-	.readdir	= ext3_readdir,		/* we take BKL. needed?*/
-	.unlocked_ioctl	= ext3_ioctl,
-#ifdef CONFIG_COMPAT
-	.compat_ioctl	= ext3_compat_ioctl,
-#endif
-	.fsync		= ext3_sync_file,	/* BKL held */
-	.release	= ext3_release_dir,
-};
-
 
 static unsigned char get_dtype(struct super_block *sb, int filetype)
 {
@@ -55,6 +40,25 @@ static unsigned char get_dtype(struct super_block *sb, int filetype)
 	return (ext3_filetype_table[filetype]);
 }
 
+/**
+ * Check if the given dir-inode refers to an htree-indexed directory
+ * (or a directory which chould potentially get coverted to use htree
+ * indexing).
+ *
+ * Return 1 if it is a dx dir, 0 if not
+ */
+static int is_dx_dir(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+
+	if (EXT3_HAS_COMPAT_FEATURE(inode->i_sb,
+		     EXT3_FEATURE_COMPAT_DIR_INDEX) &&
+	    ((EXT3_I(inode)->i_flags & EXT3_INDEX_FL) ||
+	     ((inode->i_size >> sb->s_blocksize_bits) == 1)))
+		return 1;
+
+	return 0;
+}
 
 int ext3_check_dir_entry (const char * function, struct inode * dir,
 			  struct ext3_dir_entry_2 * de,
@@ -94,18 +98,13 @@ static int ext3_readdir(struct file * filp,
 	unsigned long offset;
 	int i, stored;
 	struct ext3_dir_entry_2 *de;
-	struct super_block *sb;
 	int err;
 	struct inode *inode = filp->f_path.dentry->d_inode;
+	struct super_block *sb = inode->i_sb;
 	int ret = 0;
 	int dir_has_error = 0;
 
-	sb = inode->i_sb;
-
-	if (EXT3_HAS_COMPAT_FEATURE(inode->i_sb,
-				    EXT3_FEATURE_COMPAT_DIR_INDEX) &&
-	    ((EXT3_I(inode)->i_flags & EXT3_INDEX_FL) ||
-	     ((inode->i_size >> sb->s_blocksize_bits) == 1))) {
+	if (is_dx_dir(inode)) {
 		err = ext3_dx_readdir(filp, dirent, filldir);
 		if (err != ERR_BAD_DX_DIR) {
 			ret = err;
@@ -227,22 +226,87 @@ out:
 	return ret;
 }
 
+static inline int is_32bit_api(void)
+{
+#ifdef CONFIG_COMPAT
+	return is_compat_task();
+#else
+	return (BITS_PER_LONG == 32);
+#endif
+}
+
 /*
  * These functions convert from the major/minor hash to an f_pos
- * value.
+ * value for dx directories
  *
- * Currently we only use major hash numer.  This is unfortunate, but
- * on 32-bit machines, the same VFS interface is used for lseek and
- * llseek, so if we use the 64 bit offset, then the 32-bit versions of
- * lseek/telldir/seekdir will blow out spectacularly, and from within
- * the ext2 low-level routine, we don't know if we're being called by
- * a 64-bit version of the system call or the 32-bit version of the
- * system call.  Worse yet, NFSv2 only allows for a 32-bit readdir
- * cookie.  Sigh.
+ * Upper layer (for example NFS) should specify FMODE_32BITHASH or
+ * FMODE_64BITHASH explicitly. On the other hand, we allow ext3 to be mounted
+ * directly on both 32-bit and 64-bit nodes, under such case, neither
+ * FMODE_32BITHASH nor FMODE_64BITHASH is specified.
  */
-#define hash2pos(major, minor)	(major >> 1)
-#define pos2maj_hash(pos)	((pos << 1) & 0xffffffff)
-#define pos2min_hash(pos)	(0)
+static inline loff_t hash2pos(struct file *filp, __u32 major, __u32 minor)
+{
+	if ((filp->f_mode & FMODE_32BITHASH) ||
+	    (!(filp->f_mode & FMODE_64BITHASH) && is_32bit_api()))
+		return major >> 1;
+	else
+		return ((__u64)(major >> 1) << 32) | (__u64)minor;
+}
+
+static inline __u32 pos2maj_hash(struct file *filp, loff_t pos)
+{
+	if ((filp->f_mode & FMODE_32BITHASH) ||
+	    (!(filp->f_mode & FMODE_64BITHASH) && is_32bit_api()))
+		return (pos << 1) & 0xffffffff;
+	else
+		return ((pos >> 32) << 1) & 0xffffffff;
+}
+
+static inline __u32 pos2min_hash(struct file *filp, loff_t pos)
+{
+	if ((filp->f_mode & FMODE_32BITHASH) ||
+	    (!(filp->f_mode & FMODE_64BITHASH) && is_32bit_api()))
+		return 0;
+	else
+		return pos & 0xffffffff;
+}
+
+/*
+ * Return 32- or 64-bit end-of-file for dx directories
+ */
+static inline loff_t ext3_get_htree_eof(struct file *filp)
+{
+	if ((filp->f_mode & FMODE_32BITHASH) ||
+	    (!(filp->f_mode & FMODE_64BITHASH) && is_32bit_api()))
+		return EXT3_HTREE_EOF_32BIT;
+	else
+		return EXT3_HTREE_EOF_64BIT;
+}
+
+
+/*
+ * ext3_dir_llseek() calls generic_file_llseek[_size]() to handle both
+ * non-htree and htree directories, where the "offset" is in terms
+ * of the filename hash value instead of the byte offset.
+ *
+ * Because we may return a 64-bit hash that is well beyond s_maxbytes,
+ * we need to pass the max hash as the maximum allowable offset in
+ * the htree directory case.
+ *
+ * NOTE: offsets obtained *before* ext3_set_inode_flag(dir, EXT3_INODE_INDEX)
+ *       will be invalid once the directory was converted into a dx directory
+ */
+loff_t ext3_dir_llseek(struct file *file, loff_t offset, int origin)
+{
+	struct inode *inode = file->f_mapping->host;
+	int dx_dir = is_dx_dir(inode);
+
+	if (likely(dx_dir))
+		return generic_file_llseek_size(file, offset, origin,
+					        ext3_get_htree_eof(file));
+	else
+		return generic_file_llseek(file, offset, origin);
+}
 
 /*
  * This structure holds the nodes of the red-black tree used to store
@@ -303,15 +367,16 @@ static void free_rb_tree_fname(struct rb_root *root)
 }
 
 
-static struct dir_private_info *ext3_htree_create_dir_info(loff_t pos)
+static struct dir_private_info *ext3_htree_create_dir_info(struct file *filp,
+							   loff_t pos)
 {
 	struct dir_private_info *p;
 
 	p = kzalloc(sizeof(struct dir_private_info), GFP_KERNEL);
 	if (!p)
 		return NULL;
-	p->curr_hash = pos2maj_hash(pos);
-	p->curr_minor_hash = pos2min_hash(pos);
+	p->curr_hash = pos2maj_hash(filp, pos);
+	p->curr_minor_hash = pos2min_hash(filp, pos);
 	return p;
 }
 
@@ -401,7 +466,7 @@ static int call_filldir(struct file * filp, void * dirent,
 		printk("call_filldir: called with null fname?!?\n");
 		return 0;
 	}
-	curr_pos = hash2pos(fname->hash, fname->minor_hash);
+	curr_pos = hash2pos(filp, fname->hash, fname->minor_hash);
 	while (fname) {
 		error = filldir(dirent, fname->name,
 				fname->name_len, curr_pos,
@@ -426,13 +491,13 @@ static int ext3_dx_readdir(struct file * filp,
 	int	ret;
 
 	if (!info) {
-		info = ext3_htree_create_dir_info(filp->f_pos);
+		info = ext3_htree_create_dir_info(filp, filp->f_pos);
 		if (!info)
 			return -ENOMEM;
 		filp->private_data = info;
 	}
 
-	if (filp->f_pos == EXT3_HTREE_EOF)
+	if (filp->f_pos == ext3_get_htree_eof(filp))
 		return 0;	/* EOF */
 
 	/* Some one has messed with f_pos; reset the world */
@@ -440,8 +505,8 @@ static int ext3_dx_readdir(struct file * filp,
 		free_rb_tree_fname(&info->root);
 		info->curr_node = NULL;
 		info->extra_fname = NULL;
-		info->curr_hash = pos2maj_hash(filp->f_pos);
-		info->curr_minor_hash = pos2min_hash(filp->f_pos);
+		info->curr_hash = pos2maj_hash(filp, filp->f_pos);
+		info->curr_minor_hash = pos2min_hash(filp, filp->f_pos);
 	}
 
 	/*
@@ -473,7 +538,7 @@ static int ext3_dx_readdir(struct file * filp,
 			if (ret < 0)
 				return ret;
 			if (ret == 0) {
-				filp->f_pos = EXT3_HTREE_EOF;
+				filp->f_pos = ext3_get_htree_eof(filp);
 				break;
 			}
 			info->curr_node = rb_first(&info->root);
@@ -493,7 +558,7 @@ static int ext3_dx_readdir(struct file * filp,
 			info->curr_minor_hash = fname->minor_hash;
 		} else {
 			if (info->next_hash == ~0) {
-				filp->f_pos = EXT3_HTREE_EOF;
+				filp->f_pos = ext3_get_htree_eof(filp);
 				break;
 			}
 			info->curr_hash = info->next_hash;
@@ -512,3 +577,15 @@ static int ext3_release_dir (struct inode * inode, struct file * filp)
 
 	return 0;
 }
+
+const struct file_operations ext3_dir_operations = {
+	.llseek		= ext3_dir_llseek,
+	.read		= generic_read_dir,
+	.readdir	= ext3_readdir,
+	.unlocked_ioctl = ext3_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl	= ext3_compat_ioctl,
+#endif
+	.fsync		= ext3_sync_file,
+	.release	= ext3_release_dir,
+};
diff --git a/fs/ext3/ext3.h b/fs/ext3/ext3.h
index 7977973a24f..e85ff15a060 100644
--- a/fs/ext3/ext3.h
+++ b/fs/ext3/ext3.h
@@ -920,7 +920,11 @@ struct dx_hash_info
 	u32		*seed;
 };
 
-#define EXT3_HTREE_EOF	0x7fffffff
+
+/* 32 and 64 bit signed EOF for dx directories */
+#define EXT3_HTREE_EOF_32BIT   ((1UL  << (32 - 1)) - 1)
+#define EXT3_HTREE_EOF_64BIT   ((1ULL << (64 - 1)) - 1)
+
 
 /*
  * Control parameters used by ext3_htree_next_block
diff --git a/fs/ext3/hash.c b/fs/ext3/hash.c
index d10231ddcf8..ede315cdf12 100644
--- a/fs/ext3/hash.c
+++ b/fs/ext3/hash.c
@@ -198,8 +198,8 @@ int ext3fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
 		return -1;
 	}
 	hash = hash & ~1;
-	if (hash == (EXT3_HTREE_EOF << 1))
-		hash = (EXT3_HTREE_EOF-1) << 1;
+	if (hash == (EXT3_HTREE_EOF_32BIT << 1))
+		hash = (EXT3_HTREE_EOF_32BIT - 1) << 1;
 	hinfo->hash = hash;
 	hinfo->minor_hash = minor_hash;
 	return 0;
diff --git a/fs/ext3/ialloc.c b/fs/ext3/ialloc.c
index e3c39e4cec1..082afd78b10 100644
--- a/fs/ext3/ialloc.c
+++ b/fs/ext3/ialloc.c
@@ -180,8 +180,7 @@ error_return:
  * It's OK to put directory into a group unless
  * it has too many directories already (max_dirs) or
  * it has too few free inodes left (min_inodes) or
- * it has too few free blocks left (min_blocks) or
- * it's already running too large debt (max_debt).
+ * it has too few free blocks left (min_blocks).
  * Parent's group is preferred, if it doesn't satisfy these
  * conditions we search cyclically through the rest. If none
  * of the groups look good we just look for a group with more
@@ -191,21 +190,16 @@ error_return:
  * when we allocate an inode, within 0--255.
  */
 
-#define INODE_COST 64
-#define BLOCK_COST 256
-
 static int find_group_orlov(struct super_block *sb, struct inode *parent)
 {
 	int parent_group = EXT3_I(parent)->i_block_group;
 	struct ext3_sb_info *sbi = EXT3_SB(sb);
-	struct ext3_super_block *es = sbi->s_es;
 	int ngroups = sbi->s_groups_count;
 	int inodes_per_group = EXT3_INODES_PER_GROUP(sb);
 	unsigned int freei, avefreei;
 	ext3_fsblk_t freeb, avefreeb;
-	ext3_fsblk_t blocks_per_dir;
 	unsigned int ndirs;
-	int max_debt, max_dirs, min_inodes;
+	int max_dirs, min_inodes;
 	ext3_grpblk_t min_blocks;
 	int group = -1, i;
 	struct ext3_group_desc *desc;
@@ -242,20 +236,10 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent)
 		goto fallback;
 	}
 
-	blocks_per_dir = (le32_to_cpu(es->s_blocks_count) - freeb) / ndirs;
-
 	max_dirs = ndirs / ngroups + inodes_per_group / 16;
 	min_inodes = avefreei - inodes_per_group / 4;
 	min_blocks = avefreeb - EXT3_BLOCKS_PER_GROUP(sb) / 4;
 
-	max_debt = EXT3_BLOCKS_PER_GROUP(sb) / max(blocks_per_dir, (ext3_fsblk_t)BLOCK_COST);
-	if (max_debt * INODE_COST > inodes_per_group)
-		max_debt = inodes_per_group / INODE_COST;
-	if (max_debt > 255)
-		max_debt = 255;
-	if (max_debt == 0)
-		max_debt = 1;
-
 	for (i = 0; i < ngroups; i++) {
 		group = (parent_group + i) % ngroups;
 		desc = ext3_get_group_desc (sb, group, NULL);
diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 94ef7e61612..8c3a44b7c37 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -3015,7 +3015,6 @@ static ssize_t ext3_quota_write(struct super_block *sb, int type,
 			(unsigned long long)off, (unsigned long long)len);
 		return -EIO;
 	}
-	mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
 	bh = ext3_bread(handle, inode, blk, 1, &err);
 	if (!bh)
 		goto out;
@@ -3039,10 +3038,8 @@ static ssize_t ext3_quota_write(struct super_block *sb, int type,
 	}
 	brelse(bh);
 out:
-	if (err) {
-		mutex_unlock(&inode->i_mutex);
+	if (err)
 		return err;
-	}
 	if (inode->i_size < off + len) {
 		i_size_write(inode, off + len);
 		EXT3_I(inode)->i_disksize = inode->i_size;
@@ -3050,7 +3047,6 @@ out:
 	inode->i_version++;
 	inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 	ext3_mark_inode_dirty(handle, inode);
-	mutex_unlock(&inode->i_mutex);
 	return len;
 }
 
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 436b4223df6..1867a98e0c4 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4758,7 +4758,6 @@ static ssize_t ext4_quota_write(struct super_block *sb, int type,
 		return -EIO;
 	}
 
-	mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
 	bh = ext4_bread(handle, inode, blk, 1, &err);
 	if (!bh)
 		goto out;
@@ -4774,16 +4773,13 @@ static ssize_t ext4_quota_write(struct super_block *sb, int type,
 	err = ext4_handle_dirty_metadata(handle, NULL, bh);
 	brelse(bh);
 out:
-	if (err) {
-		mutex_unlock(&inode->i_mutex);
+	if (err)
 		return err;
-	}
 	if (inode->i_size < off + len) {
 		i_size_write(inode, off + len);
 		EXT4_I(inode)->i_disksize = inode->i_size;
 		ext4_mark_inode_dirty(handle, inode);
 	}
-	mutex_unlock(&inode->i_mutex);
 	return len;
 }
 
diff --git a/fs/jbd/checkpoint.c b/fs/jbd/checkpoint.c
index 05f0754f2b4..08c03044abd 100644
--- a/fs/jbd/checkpoint.c
+++ b/fs/jbd/checkpoint.c
@@ -508,20 +508,19 @@ int cleanup_journal_tail(journal_t *journal)
 	/*
 	 * We need to make sure that any blocks that were recently written out
 	 * --- perhaps by log_do_checkpoint() --- are flushed out before we
-	 * drop the transactions from the journal. It's unlikely this will be
-	 * necessary, especially with an appropriately sized journal, but we
-	 * need this to guarantee correctness.  Fortunately
-	 * cleanup_journal_tail() doesn't get called all that often.
+	 * drop the transactions from the journal. Similarly we need to be sure
+	 * superblock makes it to disk before next transaction starts reusing
+	 * freed space (otherwise we could replay some blocks of the new
+	 * transaction thinking they belong to the old one). So we use
+	 * WRITE_FLUSH_FUA. It's unlikely this will be necessary, especially
+	 * with an appropriately sized journal, but we need this to guarantee
+	 * correctness.  Fortunately cleanup_journal_tail() doesn't get called
+	 * all that often.
 	 */
-	if (journal->j_flags & JFS_BARRIER)
-		blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL);
+	journal_update_sb_log_tail(journal, first_tid, blocknr,
+				   WRITE_FLUSH_FUA);
 
 	spin_lock(&journal->j_state_lock);
-	if (!tid_gt(first_tid, journal->j_tail_sequence)) {
-		spin_unlock(&journal->j_state_lock);
-		/* Someone else cleaned up journal so return 0 */
-		return 0;
-	}
 	/* OK, update the superblock to recover the freed space.
 	 * Physical blocks come first: have we wrapped beyond the end of
 	 * the log?  */
@@ -539,8 +538,6 @@ int cleanup_journal_tail(journal_t *journal)
 	journal->j_tail_sequence = first_tid;
 	journal->j_tail = blocknr;
 	spin_unlock(&journal->j_state_lock);
-	if (!(journal->j_flags & JFS_ABORT))
-		journal_update_superblock(journal, 1);
 	return 0;
 }
 
diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
index f2b9a571f4c..52c15c77602 100644
--- a/fs/jbd/commit.c
+++ b/fs/jbd/commit.c
@@ -298,6 +298,7 @@ void journal_commit_transaction(journal_t *journal)
 	int tag_flag;
 	int i;
 	struct blk_plug plug;
+	int write_op = WRITE;
 
 	/*
 	 * First job: lock down the current transaction and wait for
@@ -307,7 +308,16 @@ void journal_commit_transaction(journal_t *journal)
 	/* Do we need to erase the effects of a prior journal_flush? */
 	if (journal->j_flags & JFS_FLUSHED) {
 		jbd_debug(3, "super block updated\n");
-		journal_update_superblock(journal, 1);
+		mutex_lock(&journal->j_checkpoint_mutex);
+		/*
+		 * We hold j_checkpoint_mutex so tail cannot change under us.
+		 * We don't need any special data guarantees for writing sb
+		 * since journal is empty and it is ok for write to be
+		 * flushed only with transaction commit.
+		 */
+		journal_update_sb_log_tail(journal, journal->j_tail_sequence,
+					   journal->j_tail, WRITE_SYNC);
+		mutex_unlock(&journal->j_checkpoint_mutex);
 	} else {
 		jbd_debug(3, "superblock not updated\n");
 	}
@@ -413,13 +423,16 @@ void journal_commit_transaction(journal_t *journal)
 
 	jbd_debug (3, "JBD: commit phase 2\n");
 
+	if (tid_geq(journal->j_commit_waited, commit_transaction->t_tid))
+		write_op = WRITE_SYNC;
+
 	/*
 	 * Now start flushing things to disk, in the order they appear
 	 * on the transaction lists.  Data blocks go first.
 	 */
 	blk_start_plug(&plug);
 	err = journal_submit_data_buffers(journal, commit_transaction,
-					  WRITE_SYNC);
+					  write_op);
 	blk_finish_plug(&plug);
 
 	/*
@@ -478,7 +491,7 @@ void journal_commit_transaction(journal_t *journal)
 
 	blk_start_plug(&plug);
 
-	journal_write_revoke_records(journal, commit_transaction, WRITE_SYNC);
+	journal_write_revoke_records(journal, commit_transaction, write_op);
 
 	/*
 	 * If we found any dirty or locked buffers, then we should have
@@ -649,7 +662,7 @@ start_journal_io:
 				clear_buffer_dirty(bh);
 				set_buffer_uptodate(bh);
 				bh->b_end_io = journal_end_buffer_io_sync;
-				submit_bh(WRITE_SYNC, bh);
+				submit_bh(write_op, bh);
 			}
 			cond_resched();
 
diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index 0971e921780..425c2f2cf17 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -563,6 +563,8 @@ int log_wait_commit(journal_t *journal, tid_t tid)
 	spin_unlock(&journal->j_state_lock);
 #endif
 	spin_lock(&journal->j_state_lock);
+	if (!tid_geq(journal->j_commit_waited, tid))
+		journal->j_commit_waited = tid;
 	while (tid_gt(tid, journal->j_commit_sequence)) {
 		jbd_debug(1, "JBD: want %d, j_commit_sequence=%d\n",
 				  tid, journal->j_commit_sequence);
@@ -921,8 +923,33 @@ static int journal_reset(journal_t *journal)
 
 	journal->j_max_transaction_buffers = journal->j_maxlen / 4;
 
-	/* Add the dynamic fields and write it to disk. */
-	journal_update_superblock(journal, 1);
+	/*
+	 * As a special case, if the on-disk copy is already marked as needing
+	 * no recovery (s_start == 0), then we can safely defer the superblock
+	 * update until the next commit by setting JFS_FLUSHED.  This avoids
+	 * attempting a write to a potential-readonly device.
+	 */
+	if (sb->s_start == 0) {
+		jbd_debug(1,"JBD: Skipping superblock update on recovered sb "
+			"(start %u, seq %d, errno %d)\n",
+			journal->j_tail, journal->j_tail_sequence,
+			journal->j_errno);
+		journal->j_flags |= JFS_FLUSHED;
+	} else {
+		/* Lock here to make assertions happy... */
+		mutex_lock(&journal->j_checkpoint_mutex);
+		/*
+		 * Update log tail information. We use WRITE_FUA since new
+		 * transaction will start reusing journal space and so we
+		 * must make sure information about current log tail is on
+		 * disk before that.
+		 */
+		journal_update_sb_log_tail(journal,
+					   journal->j_tail_sequence,
+					   journal->j_tail,
+					   WRITE_FUA);
+		mutex_unlock(&journal->j_checkpoint_mutex);
+	}
 	return journal_start_thread(journal);
 }
 
@@ -999,35 +1026,15 @@ int journal_create(journal_t *journal)
 	return journal_reset(journal);
 }
 
-/**
- * void journal_update_superblock() - Update journal sb on disk.
- * @journal: The journal to update.
- * @wait: Set to '0' if you don't want to wait for IO completion.
- *
- * Update a journal's dynamic superblock fields and write it to disk,
- * optionally waiting for the IO to complete.
- */
-void journal_update_superblock(journal_t *journal, int wait)
+static void journal_write_superblock(journal_t *journal, int write_op)
 {
-	journal_superblock_t *sb = journal->j_superblock;
 	struct buffer_head *bh = journal->j_sb_buffer;
+	int ret;
 
-	/*
-	 * As a special case, if the on-disk copy is already marked as needing
-	 * no recovery (s_start == 0) and there are no outstanding transactions
-	 * in the filesystem, then we can safely defer the superblock update
-	 * until the next commit by setting JFS_FLUSHED.  This avoids
-	 * attempting a write to a potential-readonly device.
-	 */
-	if (sb->s_start == 0 && journal->j_tail_sequence ==
-				journal->j_transaction_sequence) {
-		jbd_debug(1,"JBD: Skipping superblock update on recovered sb "
-			"(start %u, seq %d, errno %d)\n",
-			journal->j_tail, journal->j_tail_sequence,
-			journal->j_errno);
-		goto out;
-	}
-
+	trace_journal_write_superblock(journal, write_op);
+	if (!(journal->j_flags & JFS_BARRIER))
+		write_op &= ~(REQ_FUA | REQ_FLUSH);
+	lock_buffer(bh);
 	if (buffer_write_io_error(bh)) {
 		char b[BDEVNAME_SIZE];
 		/*
@@ -1045,42 +1052,100 @@ void journal_update_superblock(journal_t *journal, int wait)
 		set_buffer_uptodate(bh);
 	}
 
+	get_bh(bh);
+	bh->b_end_io = end_buffer_write_sync;
+	ret = submit_bh(write_op, bh);
+	wait_on_buffer(bh);
+	if (buffer_write_io_error(bh)) {
+		clear_buffer_write_io_error(bh);
+		set_buffer_uptodate(bh);
+		ret = -EIO;
+	}
+	if (ret) {
+		char b[BDEVNAME_SIZE];
+		printk(KERN_ERR "JBD: Error %d detected "
+		       "when updating journal superblock for %s.\n",
+		       ret, journal_dev_name(journal, b));
+	}
+}
+
+/**
+ * journal_update_sb_log_tail() - Update log tail in journal sb on disk.
+ * @journal: The journal to update.
+ * @tail_tid: TID of the new transaction at the tail of the log
+ * @tail_block: The first block of the transaction at the tail of the log
+ * @write_op: With which operation should we write the journal sb
+ *
+ * Update a journal's superblock information about log tail and write it to
+ * disk, waiting for the IO to complete.
+ */
+void journal_update_sb_log_tail(journal_t *journal, tid_t tail_tid,
+				unsigned int tail_block, int write_op)
+{
+	journal_superblock_t *sb = journal->j_superblock;
+
+	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
+	jbd_debug(1,"JBD: updating superblock (start %u, seq %u)\n",
+		  tail_block, tail_tid);
+
+	sb->s_sequence = cpu_to_be32(tail_tid);
+	sb->s_start    = cpu_to_be32(tail_block);
+
+	journal_write_superblock(journal, write_op);
+
+	/* Log is no longer empty */
+	spin_lock(&journal->j_state_lock);
+	WARN_ON(!sb->s_sequence);
+	journal->j_flags &= ~JFS_FLUSHED;
+	spin_unlock(&journal->j_state_lock);
+}
+
+/**
+ * mark_journal_empty() - Mark on disk journal as empty.
+ * @journal: The journal to update.
+ *
+ * Update a journal's dynamic superblock fields to show that journal is empty.
+ * Write updated superblock to disk waiting for IO to complete.
+ */
+static void mark_journal_empty(journal_t *journal)
+{
+	journal_superblock_t *sb = journal->j_superblock;
+
+	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
 	spin_lock(&journal->j_state_lock);
-	jbd_debug(1,"JBD: updating superblock (start %u, seq %d, errno %d)\n",
-		  journal->j_tail, journal->j_tail_sequence, journal->j_errno);
+	jbd_debug(1, "JBD: Marking journal as empty (seq %d)\n",
+        	  journal->j_tail_sequence);
 
 	sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
-	sb->s_start    = cpu_to_be32(journal->j_tail);
-	sb->s_errno    = cpu_to_be32(journal->j_errno);
+	sb->s_start    = cpu_to_be32(0);
 	spin_unlock(&journal->j_state_lock);
 
-	BUFFER_TRACE(bh, "marking dirty");
-	mark_buffer_dirty(bh);
-	if (wait) {
-		sync_dirty_buffer(bh);
-		if (buffer_write_io_error(bh)) {
-			char b[BDEVNAME_SIZE];
-			printk(KERN_ERR "JBD: I/O error detected "
-			       "when updating journal superblock for %s.\n",
-			       journal_dev_name(journal, b));
-			clear_buffer_write_io_error(bh);
-			set_buffer_uptodate(bh);
-		}
-	} else
-		write_dirty_buffer(bh, WRITE);
+	journal_write_superblock(journal, WRITE_FUA);
 
-	trace_jbd_update_superblock_end(journal, wait);
-out:
-	/* If we have just flushed the log (by marking s_start==0), then
-	 * any future commit will have to be careful to update the
-	 * superblock again to re-record the true start of the log. */
+	spin_lock(&journal->j_state_lock);
+	/* Log is empty */
+	journal->j_flags |= JFS_FLUSHED;
+	spin_unlock(&journal->j_state_lock);
+}
+
+/**
+ * journal_update_sb_errno() - Update error in the journal.
+ * @journal: The journal to update.
+ *
+ * Update a journal's errno.  Write updated superblock to disk waiting for IO
+ * to complete.
+ */
+static void journal_update_sb_errno(journal_t *journal)
+{
+	journal_superblock_t *sb = journal->j_superblock;
 
 	spin_lock(&journal->j_state_lock);
-	if (sb->s_start)
-		journal->j_flags &= ~JFS_FLUSHED;
-	else
-		journal->j_flags |= JFS_FLUSHED;
+	jbd_debug(1, "JBD: updating superblock error (errno %d)\n",
+        	  journal->j_errno);
+	sb->s_errno = cpu_to_be32(journal->j_errno);
 	spin_unlock(&journal->j_state_lock);
+
+	journal_write_superblock(journal, WRITE_SYNC);
 }
 
 /*
@@ -1251,6 +1316,8 @@ int journal_destroy(journal_t *journal)
 
 	/* Force any old transactions to disk */
 
+	/* We cannot race with anybody but must keep assertions happy */
+	mutex_lock(&journal->j_checkpoint_mutex);
 	/* Totally anal locking here... */
 	spin_lock(&journal->j_list_lock);
 	while (journal->j_checkpoint_transactions != NULL) {
@@ -1266,16 +1333,14 @@ int journal_destroy(journal_t *journal)
 
 	if (journal->j_sb_buffer) {
 		if (!is_journal_aborted(journal)) {
-			/* We can now mark the journal as empty. */
-			journal->j_tail = 0;
 			journal->j_tail_sequence =
 				++journal->j_transaction_sequence;
-			journal_update_superblock(journal, 1);
-		} else {
+			mark_journal_empty(journal);
+		} else
 			err = -EIO;
-		}
 		brelse(journal->j_sb_buffer);
 	}
+	mutex_unlock(&journal->j_checkpoint_mutex);
 
 	if (journal->j_inode)
 		iput(journal->j_inode);
@@ -1455,7 +1520,6 @@ int journal_flush(journal_t *journal)
 {
 	int err = 0;
 	transaction_t *transaction = NULL;
-	unsigned int old_tail;
 
 	spin_lock(&journal->j_state_lock);
 
@@ -1490,6 +1554,7 @@ int journal_flush(journal_t *journal)
 	if (is_journal_aborted(journal))
 		return -EIO;
 
+	mutex_lock(&journal->j_checkpoint_mutex);
 	cleanup_journal_tail(journal);
 
 	/* Finally, mark the journal as really needing no recovery.
@@ -1497,14 +1562,9 @@ int journal_flush(journal_t *journal)
 	 * the magic code for a fully-recovered superblock.  Any future
 	 * commits of data to the journal will restore the current
 	 * s_start value. */
+	mark_journal_empty(journal);
+	mutex_unlock(&journal->j_checkpoint_mutex);
 	spin_lock(&journal->j_state_lock);
-	old_tail = journal->j_tail;
-	journal->j_tail = 0;
-	spin_unlock(&journal->j_state_lock);
-	journal_update_superblock(journal, 1);
-	spin_lock(&journal->j_state_lock);
-	journal->j_tail = old_tail;
-
 	J_ASSERT(!journal->j_running_transaction);
 	J_ASSERT(!journal->j_committing_transaction);
 	J_ASSERT(!journal->j_checkpoint_transactions);
@@ -1544,8 +1604,12 @@ int journal_wipe(journal_t *journal, int write)
 		write ? "Clearing" : "Ignoring");
 
 	err = journal_skip_recovery(journal);
-	if (write)
-		journal_update_superblock(journal, 1);
+	if (write) {
+		/* Lock to make assertions happy... */
+		mutex_lock(&journal->j_checkpoint_mutex);
+		mark_journal_empty(journal);
+		mutex_unlock(&journal->j_checkpoint_mutex);
+	}
 
  no_recovery:
 	return err;
@@ -1613,7 +1677,7 @@ static void __journal_abort_soft (journal_t *journal, int errno)
 	__journal_abort_hard(journal);
 
 	if (errno)
-		journal_update_superblock(journal, 1);
+		journal_update_sb_errno(journal);
 }
 
 /**
diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c
index b2a7e5244e3..febc10db5ce 100644
--- a/fs/jbd/transaction.c
+++ b/fs/jbd/transaction.c
@@ -1433,8 +1433,6 @@ int journal_stop(handle_t *handle)
 		}
 	}
 
-	if (handle->h_sync)
-		transaction->t_synchronous_commit = 1;
 	current->journal_info = NULL;
 	spin_lock(&journal->j_state_lock);
 	spin_lock(&transaction->t_handle_lock);
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index d69a1d1d7e1..10cbe841cb7 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -116,15 +116,15 @@
  * spinlock to internal buffers before writing.
  *
  * Lock ordering (including related VFS locks) is the following:
- *   i_mutex > dqonoff_sem > journal_lock > dqptr_sem > dquot->dq_lock >
+ *   dqonoff_mutex > i_mutex > journal_lock > dqptr_sem > dquot->dq_lock >
  *   dqio_mutex
+ * dqonoff_mutex > i_mutex comes from dquot_quota_sync, dquot_enable, etc.
  * The lock ordering of dqptr_sem imposed by quota code is only dqonoff_sem >
  * dqptr_sem. But filesystem has to count with the fact that functions such as
  * dquot_alloc_space() acquire dqptr_sem and they usually have to be called
  * from inside a transaction to keep filesystem consistency after a crash. Also
  * filesystems usually want to do some IO on dquot from ->mark_dirty which is
  * called with dqptr_sem held.
- * i_mutex on quota files is special (it's below dqio_mutex)
  */
 
 static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dq_list_lock);
@@ -638,7 +638,7 @@ int dquot_quota_sync(struct super_block *sb, int type, int wait)
 	dqstats_inc(DQST_SYNCS);
 	mutex_unlock(&dqopt->dqonoff_mutex);
 
-	if (!wait || (sb_dqopt(sb)->flags & DQUOT_QUOTA_SYS_FILE))
+	if (!wait || (dqopt->flags & DQUOT_QUOTA_SYS_FILE))
 		return 0;
 
 	/* This is not very clever (and fast) but currently I don't know about
@@ -652,18 +652,17 @@ int dquot_quota_sync(struct super_block *sb, int type, int wait)
 	 * Now when everything is written we can discard the pagecache so
 	 * that userspace sees the changes.
 	 */
-	mutex_lock(&sb_dqopt(sb)->dqonoff_mutex);
+	mutex_lock(&dqopt->dqonoff_mutex);
 	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
 		if (type != -1 && cnt != type)
 			continue;
 		if (!sb_has_quota_active(sb, cnt))
 			continue;
-		mutex_lock_nested(&sb_dqopt(sb)->files[cnt]->i_mutex,
-				  I_MUTEX_QUOTA);
-		truncate_inode_pages(&sb_dqopt(sb)->files[cnt]->i_data, 0);
-		mutex_unlock(&sb_dqopt(sb)->files[cnt]->i_mutex);
+		mutex_lock(&dqopt->files[cnt]->i_mutex);
+		truncate_inode_pages(&dqopt->files[cnt]->i_data, 0);
+		mutex_unlock(&dqopt->files[cnt]->i_mutex);
 	}
-	mutex_unlock(&sb_dqopt(sb)->dqonoff_mutex);
+	mutex_unlock(&dqopt->dqonoff_mutex);
 
 	return 0;
 }
@@ -907,14 +906,14 @@ static void add_dquot_ref(struct super_block *sb, int type)
 			spin_unlock(&inode->i_lock);
 			continue;
 		}
-#ifdef CONFIG_QUOTA_DEBUG
-		if (unlikely(inode_get_rsv_space(inode) > 0))
-			reserved = 1;
-#endif
 		__iget(inode);
 		spin_unlock(&inode->i_lock);
 		spin_unlock(&inode_sb_list_lock);
 
+#ifdef CONFIG_QUOTA_DEBUG
+		if (unlikely(inode_get_rsv_space(inode) > 0))
+			reserved = 1;
+#endif
 		iput(old_inode);
 		__dquot_initialize(inode, type);
 
@@ -2037,8 +2036,7 @@ int dquot_disable(struct super_block *sb, int type, unsigned int flags)
 			/* If quota was reenabled in the meantime, we have
 			 * nothing to do */
 			if (!sb_has_quota_loaded(sb, cnt)) {
-				mutex_lock_nested(&toputinode[cnt]->i_mutex,
-						  I_MUTEX_QUOTA);
+				mutex_lock(&toputinode[cnt]->i_mutex);
 				toputinode[cnt]->i_flags &= ~(S_IMMUTABLE |
 				  S_NOATIME | S_NOQUOTA);
 				truncate_inode_pages(&toputinode[cnt]->i_data,
@@ -2133,7 +2131,7 @@ static int vfs_load_quota_inode(struct inode *inode, int type, int format_id,
 		/* We don't want quota and atime on quota files (deadlocks
 		 * possible) Also nobody should write to the file - we use
 		 * special IO operations which ignore the immutable bit. */
-		mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
+		mutex_lock(&inode->i_mutex);
 		oldflags = inode->i_flags & (S_NOATIME | S_IMMUTABLE |
 					     S_NOQUOTA);
 		inode->i_flags |= S_NOQUOTA | S_NOATIME | S_IMMUTABLE;
@@ -2180,7 +2178,7 @@ out_file_init:
 	iput(inode);
 out_lock:
 	if (oldflags != -1) {
-		mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
+		mutex_lock(&inode->i_mutex);
 		/* Set the flags back (in the case of accidental quotaon()
 		 * on a wrong file we don't want to mess up the flags) */
 		inode->i_flags &= ~(S_NOATIME | S_NOQUOTA | S_IMMUTABLE);
diff --git a/fs/reiserfs/super.c b/fs/reiserfs/super.c
index 8b7616ef06d..c07b7d70944 100644
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -2270,7 +2270,6 @@ static ssize_t reiserfs_quota_write(struct super_block *sb, int type,
 			(unsigned long long)off, (unsigned long long)len);
 		return -EIO;
 	}
-	mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
 	while (towrite > 0) {
 		tocopy = sb->s_blocksize - offset < towrite ?
 		    sb->s_blocksize - offset : towrite;
@@ -2302,16 +2301,13 @@ static ssize_t reiserfs_quota_write(struct super_block *sb, int type,
 		blk++;
 	}
 out:
-	if (len == towrite) {
-		mutex_unlock(&inode->i_mutex);
+	if (len == towrite)
 		return err;
-	}
 	if (inode->i_size < off + len - towrite)
 		i_size_write(inode, off + len - towrite);
 	inode->i_version++;
 	inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 	mark_inode_dirty(inode);
-	mutex_unlock(&inode->i_mutex);
 	return len - towrite;
 }