Btrfs: Keep fs_mutex during reads done by snapshot deletion

There was an optimization to drop the fs_mutex when doing snapshot deletion
reads, but this can lead to false positives on checksumming errors.  Keep
the lock for now.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c226656f29b7..cf283b0271ac 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2046,11 +2046,12 @@ static int noinline walk_down_tree(struct btrfs_trans_handle *trans,
                 if (!next || !btrfs_buffer_uptodate(next)) {
                         free_extent_buffer(next);
                         reada_walk_down(root, cur, path->slots[*level]);
-                        mutex_unlock(&root->fs_info->fs_mutex);
                         next = read_tree_block(root, bytenr, blocksize);
-                        mutex_lock(&root->fs_info->fs_mutex);
 
-                        /* we dropped the lock, check one more time */
+                        /* we used to drop the lock above, keep the
+                         * code to double check so that we won't forget
+                         * when we drop the lock again in the future
+                         */
                         ret = lookup_extent_ref(trans, root, bytenr,
                                                 blocksize, &refs);
                         BUG_ON(ret);