btrfs: do not warn for free space inode in cow_file_range

This is a long time leftover from when I originally added the free space
inode, the point was to catch cases where we weren't honoring the NOCOW
flag.  However there exists a race with relocation, if we allocate our
free space inode in a block group that is about to be relocated, we
could trigger the COW path before the relocation has the opportunity to
find the extents and delete the free space cache.  In production where
we have auto-relocation enabled we're seeing this WARN_ON_ONCE() around
5k times in a 2 week period, so not super common but enough that it's at
the top of our metrics.

We're properly handling the error here, and with us phasing out v1 space
cache anyway just drop the WARN_ON_ONCE.

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/inode.c b/fs/btrfs/inode.c
index 2e7143ff552302444c7412f5720305f607c18797..b976f757571f5b1637a8b3a607f825be6497c62e 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1128,7 +1128,6 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
        int ret = 0;
 
        if (btrfs_is_free_space_inode(inode)) {
-               WARN_ON_ONCE(1);
                ret = -EINVAL;
                goto out_unlock;
        }