btrfs: fix ref-verify to catch operations on 0 ref extents

While debugging I noticed I wasn't getting ref verify errors before
everything blew up.  Turns out it's because we don't warn when we try to
add a normal ref via btrfs_inc_ref() if the block entry exists but has 0
references.  This is incorrect, we should never be doing anything other
than adding a new extent once a block entry drops to 0 references.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/ref-verify.c b/fs/btrfs/ref-verify.c
index 454a1015d026b741ec1a1b168375755d6df5971a..7887317033c98218a45bf710157fa37459d09b91 100644 (file)
--- a/fs/btrfs/ref-verify.c
+++ b/fs/btrfs/ref-verify.c
@@ -803,6 +803,15 @@ int btrfs_ref_tree_mod(struct btrfs_fs_info *fs_info,
                        kfree(ref);
                        kfree(ra);
                        goto out_unlock;
+               } else if (be->num_refs == 0) {
+                       btrfs_err(fs_info,
+               "trying to do action %d for a bytenr that has 0 total references",
+                               action);
+                       dump_block_entry(fs_info, be);
+                       dump_ref_action(fs_info, ra);
+                       kfree(ref);
+                       kfree(ra);
+                       goto out_unlock;
                }
 
                if (!parent) {