1 files changed, 206 insertions, 75 deletions

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 634b9ae713e..713a9722678 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -37,41 +37,59 @@
 #define ASHMEM_NAME_PREFIX_LEN (sizeof(ASHMEM_NAME_PREFIX) - 1)
 #define ASHMEM_FULL_NAME_LEN (ASHMEM_NAME_LEN + ASHMEM_NAME_PREFIX_LEN)
 
-/*
- * ashmem_area - anonymous shared memory area
- * Lifecycle: From our parent file's open() until its release()
- * Locking: Protected by `ashmem_mutex'
- * Big Note: Mappings do NOT pin this structure; it dies on close()
+/**
+ * struct ashmem_area - The anonymous shared memory area
+ * @name:		The optional name in /proc/pid/maps
+ * @unpinned_list:	The list of all ashmem areas
+ * @file:		The shmem-based backing file
+ * @size:		The size of the mapping, in bytes
+ * @prot_masks:		The allowed protection bits, as vm_flags
+ *
+ * The lifecycle of this structure is from our parent file's open() until
+ * its release(). It is also protected by 'ashmem_mutex'
+ *
+ * Warning: Mappings do NOT pin this structure; It dies on close()
  */
 struct ashmem_area {
-	char name[ASHMEM_FULL_NAME_LEN]; /* optional name in /proc/pid/maps */
-	struct list_head unpinned_list;	 /* list of all ashmem areas */
-	struct file *file;		 /* the shmem-based backing file */
-	size_t size;			 /* size of the mapping, in bytes */
-	unsigned long prot_mask;	 /* allowed prot bits, as vm_flags */
+	char name[ASHMEM_FULL_NAME_LEN];
+	struct list_head unpinned_list;
+	struct file *file;
+	size_t size;
+	unsigned long prot_mask;
 };
 
-/*
- * ashmem_range - represents an interval of unpinned (evictable) pages
- * Lifecycle: From unpin to pin
- * Locking: Protected by `ashmem_mutex'
+/**
+ * struct ashmem_range - A range of unpinned/evictable pages
+ * @lru:	         The entry in the LRU list
+ * @unpinned:	         The entry in its area's unpinned list
+ * @asma:	         The associated anonymous shared memory area.
+ * @pgstart:	         The starting page (inclusive)
+ * @pgend:	         The ending page (inclusive)
+ * @purged:	         The purge status (ASHMEM_NOT or ASHMEM_WAS_PURGED)
+ *
+ * The lifecycle of this structure is from unpin to pin.
+ * It is protected by 'ashmem_mutex'
  */
 struct ashmem_range {
-	struct list_head lru;		/* entry in LRU list */
-	struct list_head unpinned;	/* entry in its area's unpinned list */
-	struct ashmem_area *asma;	/* associated area */
-	size_t pgstart;			/* starting page, inclusive */
-	size_t pgend;			/* ending page, inclusive */
-	unsigned int purged;		/* ASHMEM_NOT or ASHMEM_WAS_PURGED */
+	struct list_head lru;
+	struct list_head unpinned;
+	struct ashmem_area *asma;
+	size_t pgstart;
+	size_t pgend;
+	unsigned int purged;
 };
 
 /* LRU list of unpinned pages, protected by ashmem_mutex */
 static LIST_HEAD(ashmem_lru_list);
 
-/* Count of pages on our LRU list, protected by ashmem_mutex */
+/**
+ * long lru_count - The count of pages on our LRU list.
+ *
+ * This is protected by ashmem_mutex.
+ */
 static unsigned long lru_count;
 
-/*
+/**
  * ashmem_mutex - protects the list of and each individual ashmem_area
  *
  * Lock Ordering: ashmex_mutex -> i_mutex -> i_alloc_sem
@@ -105,28 +123,43 @@ static struct kmem_cache *ashmem_range_cachep __read_mostly;
 
 #define PROT_MASK		(PROT_EXEC | PROT_READ | PROT_WRITE)
 
+/**
+ * lru_add() - Adds a range of memory to the LRU list
+ * @range:     The memory range being added.
+ *
+ * The range is first added to the end (tail) of the LRU list.
+ * After this, the size of the range is added to @lru_count
+ */
 static inline void lru_add(struct ashmem_range *range)
 {
 	list_add_tail(&range->lru, &ashmem_lru_list);
 	lru_count += range_size(range);
 }
 
+/**
+ * lru_del() - Removes a range of memory from the LRU list
+ * @range:     The memory range being removed
+ *
+ * The range is first deleted from the LRU list.
+ * After this, the size of the range is removed from @lru_count
+ */
 static inline void lru_del(struct ashmem_range *range)
 {
 	list_del(&range->lru);
 	lru_count -= range_size(range);
 }
 
-/*
- * range_alloc - allocate and initialize a new ashmem_range structure
+/**
+ * range_alloc() - Allocates and initializes a new ashmem_range structure
+ * @asma:	   The associated ashmem_area
+ * @prev_range:	   The previous ashmem_range in the sorted asma->unpinned list
+ * @purged:	   Initial purge status (ASMEM_NOT_PURGED or ASHMEM_WAS_PURGED)
+ * @start:	   The starting page (inclusive)
+ * @end:	   The ending page (inclusive)
  *
- * 'asma' - associated ashmem_area
- * 'prev_range' - the previous ashmem_range in the sorted asma->unpinned list
- * 'purged' - initial purge value (ASMEM_NOT_PURGED or ASHMEM_WAS_PURGED)
- * 'start' - starting page, inclusive
- * 'end' - ending page, inclusive
+ * This function is protected by ashmem_mutex.
  *
- * Caller must hold ashmem_mutex.
+ * Return: 0 if successful, or -ENOMEM if there is an error
  */
 static int range_alloc(struct ashmem_area *asma,
 		       struct ashmem_range *prev_range, unsigned int purged,
@@ -151,6 +184,10 @@ static int range_alloc(struct ashmem_area *asma,
 	return 0;
 }
 
+/**
+ * range_del() - Deletes and dealloctes an ashmem_range structure
+ * @range:	 The associated ashmem_range that has previously been allocated
+ */
 static void range_del(struct ashmem_range *range)
 {
 	list_del(&range->unpinned);
@@ -159,10 +196,17 @@ static void range_del(struct ashmem_range *range)
 	kmem_cache_free(ashmem_range_cachep, range);
 }
 
-/*
- * range_shrink - shrinks a range
+/**
+ * range_shrink() - Shrinks an ashmem_range
+ * @range:	    The associated ashmem_range being shrunk
+ * @start:	    The starting byte of the new range
+ * @end:	    The ending byte of the new range
  *
- * Caller must hold ashmem_mutex.
+ * This does not modify the data inside the existing range in any way - It
+ * simply shrinks the boundaries of the range.
+ *
+ * Theoretically, with a little tweaking, this could eventually be changed
+ * to range_resize, and expand the lru_count if the new range is larger.
  */
 static inline void range_shrink(struct ashmem_range *range,
 				size_t start, size_t end)
@@ -176,6 +220,16 @@ static inline void range_shrink(struct ashmem_range *range,
 		lru_count -= pre - range_size(range);
 }
 
+/**
+ * ashmem_open() - Opens an Anonymous Shared Memory structure
+ * @inode:	   The backing file's index node(?)
+ * @file:	   The backing file
+ *
+ * Please note that the ashmem_area is not returned by this function - It is
+ * instead written to "file->private_data".
+ *
+ * Return: 0 if successful, or another code if unsuccessful.
+ */
 static int ashmem_open(struct inode *inode, struct file *file)
 {
 	struct ashmem_area *asma;
@@ -197,6 +251,14 @@ static int ashmem_open(struct inode *inode, struct file *file)
 	return 0;
 }
 
+/**
+ * ashmem_release() - Releases an Anonymous Shared Memory structure
+ * @ignored:	      The backing file's Index Node(?) - It is ignored here.
+ * @file:	      The backing file
+ *
+ * Return: 0 if successful. If it is anything else, go have a coffee and
+ * try again.
+ */
 static int ashmem_release(struct inode *ignored, struct file *file)
 {
 	struct ashmem_area *asma = file->private_data;
@@ -214,6 +276,15 @@ static int ashmem_release(struct inode *ignored, struct file *file)
 	return 0;
 }
 
+/**
+ * ashmem_read() - Reads a set of bytes from an Ashmem-enabled file
+ * @file:	   The associated backing file.
+ * @buf:	   The buffer of data being written to
+ * @len:	   The number of bytes being read
+ * @pos:	   The position of the first byte to read.
+ *
+ * Return: 0 if successful, or another return code if not.
+ */
 static ssize_t ashmem_read(struct file *file, char __user *buf,
 			   size_t len, loff_t *pos)
 {
@@ -224,21 +295,29 @@ static ssize_t ashmem_read(struct file *file, char __user *buf,
 
 	/* If size is not set, or set to 0, always return EOF. */
 	if (asma->size == 0)
-		goto out;
+		goto out_unlock;
 
 	if (!asma->file) {
 		ret = -EBADF;
-		goto out;
+		goto out_unlock;
 	}
 
-	ret = asma->file->f_op->read(asma->file, buf, len, pos);
-	if (ret < 0)
-		goto out;
+	mutex_unlock(&ashmem_mutex);
 
-	/** Update backing file pos, since f_ops->read() doesn't */
-	asma->file->f_pos = *pos;
+	/*
+	 * asma and asma->file are used outside the lock here.  We assume
+	 * once asma->file is set it will never be changed, and will not
+	 * be destroyed until all references to the file are dropped and
+	 * ashmem_release is called.
+	 */
+	ret = asma->file->f_op->read(asma->file, buf, len, pos);
+	if (ret >= 0) {
+		/** Update backing file pos, since f_ops->read() doesn't */
+		asma->file->f_pos = *pos;
+	}
+	return ret;
 
-out:
+out_unlock:
 	mutex_unlock(&ashmem_mutex);
 	return ret;
 }
@@ -341,27 +420,26 @@ out:
 /*
  * ashmem_shrink - our cache shrinker, called from mm/vmscan.c :: shrink_slab
  *
- * 'nr_to_scan' is the number of objects (pages) to prune, or 0 to query how
- * many objects (pages) we have in total.
+ * 'nr_to_scan' is the number of objects to scan for freeing.
  *
  * 'gfp_mask' is the mask of the allocation that got us into this mess.
  *
- * Return value is the number of objects (pages) remaining, or -1 if we cannot
+ * Return value is the number of objects freed or -1 if we cannot
  * proceed without risk of deadlock (due to gfp_mask).
  *
  * We approximate LRU via least-recently-unpinned, jettisoning unpinned partial
  * chunks of ashmem regions LRU-wise one-at-a-time until we hit 'nr_to_scan'
  * pages freed.
  */
-static int ashmem_shrink(struct shrinker *s, struct shrink_control *sc)
+static unsigned long
+ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 {
 	struct ashmem_range *range, *next;
+	unsigned long freed = 0;
 
 	/* We might recurse into filesystem code, so bail out if necessary */
-	if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
-		return -1;
-	if (!sc->nr_to_scan)
-		return lru_count;
+	if (!(sc->gfp_mask & __GFP_FS))
+		return SHRINK_STOP;
 
 	mutex_lock(&ashmem_mutex);
 	list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) {
@@ -374,17 +452,32 @@ static int ashmem_shrink(struct shrinker *s, struct shrink_control *sc)
 		range->purged = ASHMEM_WAS_PURGED;
 		lru_del(range);
 
-		sc->nr_to_scan -= range_size(range);
-		if (sc->nr_to_scan <= 0)
+		freed += range_size(range);
+		if (--sc->nr_to_scan <= 0)
 			break;
 	}
 	mutex_unlock(&ashmem_mutex);
+	return freed;
+}
 
+static unsigned long
+ashmem_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
+{
+	/*
+	 * note that lru_count is count of pages on the lru, not a count of
+	 * objects on the list. This means the scan function needs to return the
+	 * number of pages freed, not the number of objects scanned.
+	 */
 	return lru_count;
 }
 
 static struct shrinker ashmem_shrinker = {
-	.shrink = ashmem_shrink,
+	.count_objects = ashmem_shrink_count,
+	.scan_objects = ashmem_shrink_scan,
+	/*
+	 * XXX (dchinner): I wish people would comment on why they need on
+	 * significant changes to the default value here
+	 */
 	.seeks = DEFAULT_SEEKS * 4,
 };
 
@@ -413,50 +506,68 @@ out:
 
 static int set_name(struct ashmem_area *asma, void __user *name)
 {
+	int len;
 	int ret = 0;
+	char local_name[ASHMEM_NAME_LEN];
 
+	/*
+	 * Holding the ashmem_mutex while doing a copy_from_user might cause
+	 * an data abort which would try to access mmap_sem. If another
+	 * thread has invoked ashmem_mmap then it will be holding the
+	 * semaphore and will be waiting for ashmem_mutex, there by leading to
+	 * deadlock. We'll release the mutex  and take the name to a local
+	 * variable that does not need protection and later copy the local
+	 * variable to the structure member with lock held.
+	 */
+	len = strncpy_from_user(local_name, name, ASHMEM_NAME_LEN);
+	if (len < 0)
+		return len;
+	if (len == ASHMEM_NAME_LEN)
+		local_name[ASHMEM_NAME_LEN - 1] = '\0';
 	mutex_lock(&ashmem_mutex);
-
 	/* cannot change an existing mapping's name */
-	if (unlikely(asma->file)) {
+	if (unlikely(asma->file))
 		ret = -EINVAL;
-		goto out;
-	}
+	else
+		strcpy(asma->name + ASHMEM_NAME_PREFIX_LEN, local_name);
 
-	if (unlikely(copy_from_user(asma->name + ASHMEM_NAME_PREFIX_LEN,
-				    name, ASHMEM_NAME_LEN)))
-		ret = -EFAULT;
-	asma->name[ASHMEM_FULL_NAME_LEN-1] = '\0';
-
-out:
 	mutex_unlock(&ashmem_mutex);
-
 	return ret;
 }
 
 static int get_name(struct ashmem_area *asma, void __user *name)
 {
 	int ret = 0;
+	size_t len;
+	/*
+	 * Have a local variable to which we'll copy the content
+	 * from asma with the lock held. Later we can copy this to the user
+	 * space safely without holding any locks. So even if we proceed to
+	 * wait for mmap_sem, it won't lead to deadlock.
+	 */
+	char local_name[ASHMEM_NAME_LEN];
 
 	mutex_lock(&ashmem_mutex);
 	if (asma->name[ASHMEM_NAME_PREFIX_LEN] != '\0') {
-		size_t len;
 
 		/*
 		 * Copying only `len', instead of ASHMEM_NAME_LEN, bytes
 		 * prevents us from revealing one user's stack to another.
 		 */
 		len = strlen(asma->name + ASHMEM_NAME_PREFIX_LEN) + 1;
-		if (unlikely(copy_to_user(name,
-				asma->name + ASHMEM_NAME_PREFIX_LEN, len)))
-			ret = -EFAULT;
+		memcpy(local_name, asma->name + ASHMEM_NAME_PREFIX_LEN, len);
 	} else {
-		if (unlikely(copy_to_user(name, ASHMEM_NAME_DEF,
-					  sizeof(ASHMEM_NAME_DEF))))
-			ret = -EFAULT;
+		len = sizeof(ASHMEM_NAME_DEF);
+		memcpy(local_name, ASHMEM_NAME_DEF, len);
 	}
 	mutex_unlock(&ashmem_mutex);
 
+	/*
+	 * Now we are just copying from the stack variable to userland
+	 * No lock held
+	 */
+	if (unlikely(copy_to_user(name, local_name, len)))
+		ret = -EFAULT;
 	return ret;
 }
 
@@ -671,11 +782,11 @@ static long ashmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		if (capable(CAP_SYS_ADMIN)) {
 			struct shrink_control sc = {
 				.gfp_mask = GFP_KERNEL,
-				.nr_to_scan = 0,
+				.nr_to_scan = LONG_MAX,
 			};
-			ret = ashmem_shrink(&ashmem_shrinker, &sc);
-			sc.nr_to_scan = ret;
-			ashmem_shrink(&ashmem_shrinker, &sc);
+			ret = ashmem_shrink_count(&ashmem_shrinker, &sc);
+			nodes_setall(sc.nodes_to_scan);
+			ashmem_shrink_scan(&ashmem_shrinker, &sc);
 		}
 		break;
 	}
@@ -683,6 +794,24 @@ static long ashmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	return ret;
 }
 
+/* support of 32bit userspace on 64bit platforms */
+#ifdef CONFIG_COMPAT
+static long compat_ashmem_ioctl(struct file *file, unsigned int cmd,
+				unsigned long arg)
+{
+
+	switch (cmd) {
+	case COMPAT_ASHMEM_SET_SIZE:
+		cmd = ASHMEM_SET_SIZE;
+		break;
+	case COMPAT_ASHMEM_SET_PROT_MASK:
+		cmd = ASHMEM_SET_PROT_MASK;
+		break;
+	}
+	return ashmem_ioctl(file, cmd, arg);
+}
+#endif
+
 static const struct file_operations ashmem_fops = {
 	.owner = THIS_MODULE,
 	.open = ashmem_open,
@@ -691,7 +820,9 @@ static const struct file_operations ashmem_fops = {
 	.llseek = ashmem_llseek,
 	.mmap = ashmem_mmap,
 	.unlocked_ioctl = ashmem_ioctl,
-	.compat_ioctl = ashmem_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl = compat_ashmem_ioctl,
+#endif
 };
 
 static struct miscdevice ashmem_misc = {