btrfs: raid56: do not verify the content if there is no data checksum

[BUG]
There is a bug report that fio can fail to sync the data on a degraded
RAID56 mount:

  # mkfs.btrfs -m raid1 -d raid5 -f $dev1 $dev2 $dev3
  # mount $dev1 $mnt
  # btrfs balance start -d $mnt
  # umount $mnt
  # btrfs dev scan -u $dev2
  # wipefs -fa $dev2
  # mount -o degraded $dev1 $mnt
  # fio --name=degraded-write --directory=$mnt --rw=randwrite --fdatasync=4 \
		--bs=4k --size=512M --randrepeat=1

The run will fail at fsync:

  fio: io_u error on file /mnt/btrfs/degraded-write.0.0: Input/output error: datasync offset=142254080, buflen=0
  fio: pid=2064, err=5/file:io_u.c:2008, func=io_u error, error=Input/output error

[CAUSE]
With extra debug output, it shows the problem pretty well:

  rbio=2876243968 faila=0 sectornr=0
  rbio=2876243968 error=0-15 csum=2 bio=15

The first line shows the rbio's full stripe logical, and stripe/sector
number when verify_one_sector() failed.

The second line shows more detail about the rbio, the sector range [0, 16)
is corrupted, which indicates the first data stripe is corrupted, matching
the missing device.

The important part is that the csum bitmap shows the data csum is only
for sector number 2, meanwhile the failed verification is at sector
number 0.

This means we did the checksum verification even if no corresponding
checksum is populated.

[FIX]
There is already a similar check at verify_bio_data_sectors(), but
unfortunately there is no such check at verify_one_sector().

Add the missing check to skip the csum verification if there is no
corresponding data checksum.

Reported-by: Bartosz Fenski <bartosz@fenski.pl>
Link: https://lore.kernel.org/linux-btrfs/a72409af-45ef-45df-9970-2e38bcb22ea6@fenski.pl/
Fixes: 7a3150723061 ("btrfs: raid56: do data csum verification during RMW cycle")
CC: stable@vger.kernel.org
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

0 files changed, 0 insertions, 0 deletions