Uncorrectable error during multiple scrub (raid5 recovery).

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

Uncorrectable error during multiple scrub (raid5 recovery).

This reproducer is based on some reproducer [1],
but it seems a new problem, so I open a new thread.

reproducer:

mkfs.btrfs -f -draid5 -mraid1 ${SCRATCH_DEV_POOL}
SCRATCH_DEV_ARRAY=($SCRATCH_DEV_POOL)
mount ${SCRATCH_DEV_ARRAY[0]} $SCRATCH_MNT # -o compress=zstd,noatime

/bin/cp -a /usr/bin $SCRATCH_MNT/
#(OK)dd if=/dev/urandom bs=1M count=1K of=$SCRATCH_MNT/1G.img
du -sh $SCRATCH_MNT

for((i=1;i<=15;++i)); do

	#(OK)umount $SCRATCH_MNT; mount ${SCRATCH_DEV_ARRAY[0]} $SCRATCH_MNT # -o compress=zstd,noatime
	sync; sleep 5; sync; sleep 5; sync; sleep 25;

	# change the device to discard in every loop
	j=$(( i % ${#SCRATCH_DEV_ARRAY[@]} ))
	/usr/sbin/blkdiscard -f ${SCRATCH_DEV_ARRAY[$j]} # --offset 2M

	btrfs scrub start -Bd $SCRATCH_MNT | grep 'summary\|Uncorrectable'

done

This problem will not happen if we change the test data to simpler one.
# about 220M data of '/usr/bin' to single 1G file

This problem will not happen if we clear cache with 'umount; mount'
between multiple loop.
# 'sync; sleep 5; ...' to  'umount; mount'

so it seems that some info in memory is wrong after RAID5 recovery?

[1]
Subject: misc-next and for-next: kernel BUG at fs/btrfs/extent_io.c:2350!
during raid5 recovery
https://lore.kernel.org/linux-btrfs/9dfb0b60-9178-7bbe-6ba1-10d056a7e84c@gmx.com/T/#t

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2022/08/14