Btrfs: Fix oopsen when dropping empty tree.

When dropping a empty tree, walk_down_tree() skips checking
extent information for the tree root. This will triggers a
BUG_ON in walk_up_proc().

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 432a2da4641e..559f72489b3b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5402,10 +5402,6 @@ static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
         int ret;
 
         while (level >= 0) {
-                if (path->slots[level] >=
-                    btrfs_header_nritems(path->nodes[level]))
-                        break;
-
                 ret = walk_down_proc(trans, root, path, wc, lookup_info);
                 if (ret > 0)
                         break;
@@ -5413,6 +5409,10 @@ static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
                 if (level == 0)
                         break;
 
+                if (path->slots[level] >=
+                    btrfs_header_nritems(path->nodes[level]))
+                        break;
+
                 ret = do_walk_down(trans, root, path, wc, &lookup_info);
                 if (ret > 0) {
                         path->slots[level]++;