btrfs: fix oops on failure path

If lookup_extent_backref fails, path->nodes[0] reasonably could be
null along with other callers of btrfs_print_leaf, so ensure we have a
valid extent buffer before dereferencing.

Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c
index fb2605d998e..f38e452486b 100644
--- a/fs/btrfs/print-tree.c
+++ b/fs/btrfs/print-tree.c
@@ -158,8 +158,7 @@ static void print_extent_ref_v0(struct extent_buffer *eb, int slot)
 void btrfs_print_leaf(struct btrfs_root *root, struct extent_buffer *l)
 {
         int i;
-        u32 type;
-        u32 nr = btrfs_header_nritems(l);
+        u32 type, nr;
         struct btrfs_item *item;
         struct btrfs_root_item *ri;
         struct btrfs_dir_item *di;
@@ -172,6 +171,11 @@ void btrfs_print_leaf(struct btrfs_root *root, struct extent_buffer *l)
         struct btrfs_key key;
         struct btrfs_key found_key;
 
+        if (!l)
+                return;
+
+        nr = btrfs_header_nritems(l);
+
         printk(KERN_INFO "leaf %llu total ptrs %d free space %d\n",
                 (unsigned long long)btrfs_header_bytenr(l), nr,
                 btrfs_leaf_free_space(root, l));