Re: Uncorrectable error during multiple scrub (raid5 recovery).

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2022/8/14 12:58, Wang Yugui wrote:
> Hi,
>
>> On 2022/8/14 11:10, Wang Yugui wrote:
>>> 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
>>
>> Please remove unnecessary comments if it's not explaining anything.
>>
>> It just makes the test case much harder to read.
>>>
>>> /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]} $SCRATCH_MNT # -o compress=zstd,noatime
>>> 	sync; sleep 5; sync; sleep 5; sync; sleep 25;
>>
>> If you really want to provide a reproducer, either explain why this is
>> needed or it will just waste time of everyone who is trying this test.
>>
>>>
>>> 	# change the device to discard in every loop
>>> 	j=$(( 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
>>
>> That case is in fact not related to RAID56, and we already have the fix
>> for it:
>> https://lore.kernel.org/linux-btrfs/1d9b69af6ce0a79e54fbaafcc65ead8f71b54b60.1660377678.git.wqu@suse.com/
>
> This problem still happen on  linux 5.20(20220812) with the flowing patches.

Then please provide a human readable reproducer.

The current one is not really clear which part is commented out.

>
> Subject: btrfs: scrub: properly report super block errors in system log
> Subject: btrfs: scrub: try to fix super block errors
> (v2)Subject: btrfs: don't merge pages into bio if their page offset is not
>
> Best Regards
> Wang Yugui (wangyugui@e16-tech.com)
> 2022/08/14
>
>