btrfs: Go readonly on bad extent refs in update_ref_for_cow()

update_ref_for_cow() will BUG_ON() after it's call to
btrfs_lookup_extent_info() if no existing references are found.  Since refs
are computed directly from disk, this should be treated as a corruption
instead of a logic error.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index e2e43c07f6b1..3b767d2b68e8 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -333,7 +333,11 @@ static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans,
                                                buf->len, &refs, &flags);
                 if (ret)
                         return ret;
-                BUG_ON(refs == 0);
+                if (refs == 0) {
+                        ret = -EROFS;
+                        btrfs_std_error(root->fs_info, ret);
+                        return ret;
+                }
         } else {
                 refs = 1;
                 if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||