ext4: call ext4_ext_drop_refs() from ext4_ext_find_extent()

In nearly all of the calls to ext4_ext_find_extent() where the caller
is trying to recycle the path object, ext4_ext_drop_refs() gets called
to release the buffer heads before the path object gets overwritten.
To simplify things for the callers, and to avoid the possibility of a
memory leak, make ext4_ext_find_extent() responsible for dropping the
buffers.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/extents.c

@@ -867,8 +867,10 @@ ext4_ext_find_extent(struct inode *inode, ext4_lblk_t block,
 	eh = ext_inode_hdr(inode);
 	depth = ext_depth(inode);
 
-	/* account possible depth increase */
-	if (!path) {
+	if (path)
+		ext4_ext_drop_refs(path);
+	else {
+		/* account possible depth increase */
 		path = kzalloc(sizeof(struct ext4_ext_path) * (depth + 2),
 				GFP_NOFS);
 		if (unlikely(!path))
@@ -1356,7 +1358,6 @@ repeat:
 			goto out;
 
 		/* refill path */
-		ext4_ext_drop_refs(path);
 		path = ext4_ext_find_extent(inode,
 				    (ext4_lblk_t)le32_to_cpu(newext->ee_block),
 				    ppath, gb_flags);
@@ -1369,7 +1370,6 @@ repeat:
 			goto out;
 
 		/* refill path */
-		ext4_ext_drop_refs(path);
 		path = ext4_ext_find_extent(inode,
 				   (ext4_lblk_t)le32_to_cpu(newext->ee_block),
 				    ppath, gb_flags);
@@ -3319,7 +3319,6 @@ static int ext4_split_extent(handle_t *handle,
 	 * Update path is required because previous ext4_split_extent_at() may
 	 * result in split of original leaf or extent zeroout.
 	 */
-	ext4_ext_drop_refs(path);
 	path = ext4_ext_find_extent(inode, map->m_lblk, ppath, 0);
 	if (IS_ERR(path))
 		return PTR_ERR(path);
@@ -3718,7 +3717,6 @@ static int ext4_convert_unwritten_extents_endio(handle_t *handle,
 						 EXT4_GET_BLOCKS_CONVERT);
 		if (err < 0)
 			return err;
-		ext4_ext_drop_refs(path);
 		path = ext4_ext_find_extent(inode, map->m_lblk, ppath, 0);
 		if (IS_ERR(path))
 			return PTR_ERR(path);
@@ -3947,7 +3945,6 @@ convert_initialized_extent(handle_t *handle, struct inode *inode,
 				EXT4_GET_BLOCKS_CONVERT_UNWRITTEN);
 		if (err < 0)
 			return err;
-		ext4_ext_drop_refs(path);
 		path = ext4_ext_find_extent(inode, map->m_lblk, ppath, 0);
 		if (IS_ERR(path))
 			return PTR_ERR(path);