When I implemented the storage layer bio splitting, I was under the
assumption that we'll never split metadata bios.  But Qu reminded me that
this can actually happen with very old file systems with unaligned
metadata chunks and RAID0.

I still haven't seen such a case in practice, but we better handled this
case, especially as it is fairly easily to do not calling the ->end_іo
method directly in btrfs_end_io_work, and using the proper
btrfs_orig_bbio_end_io helper instead.

In addition to the old file system with unaligned metadata chunks case
documented in the commit log, the combination of the new scrub code
with Johannes pending raid-stripe-tree also triggers this case.  We
spent some time debugging it and found that this patch solves
the problem.

Fixes: 103c1972 ("btrfs: split the bio submission path into a separate file")
CC: stable@vger.kernel.org # 6.3+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Tested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>