Re: [PATCH tests 5/5] tests: add a regression test for raid456 deadlock

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

On Tue, 23 May 2023 21:39:00 +0800
Yu Kuai <yukuai1@huaweicloud.com> wrote:

> From: Yu Kuai <yukuai3@huawei.com>
> 
> The deadlock is described in [1], as the last patch described, it's
> fixed first by [2], however this fix will be reverted and the deadlock
> is supposed to be fixed by [3].
> 
> [1]
> https://lore.kernel.org/linux-raid/5ed54ffc-ce82-bf66-4eff-390cb23bc1ac@molgen.mpg.de/T/#t
> [2]
> https://lore.kernel.org/linux-raid/20220621031129.24778-1-guoqing.jiang@linux.dev/
> [3]
> https://lore.kernel.org/linux-raid/20230322064122.2384589-5-yukuai1@huaweicloud.com/
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  tests/24raid456deadlock | 56 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
>  create mode 100644 tests/24raid456deadlock
> 
> diff --git a/tests/24raid456deadlock b/tests/24raid456deadlock
> new file mode 100644
> index 00000000..161c3ab8
> --- /dev/null
> +++ b/tests/24raid456deadlock
> @@ -0,0 +1,56 @@
> +devs="$dev0 $dev1 $dev2 $dev3 $dev4 $dev5"
> +runtime=120
> +pid=""
> +old=`cat /proc/sys/vm/dirty_background_ratio`
> +
> +test_write_action()
> +{
> +	while true; do
> +		echo check > /sys/block/md0/md/sync_action &> /dev/null
> +		sleep 0.1
> +		echo idle > /sys/block/md0/md/sync_action &> /dev/null
> +	done
> +}
> +
> +test_write_back()
> +{
> +	fio -filename=$md0 -bs=4k -rw=write -numjobs=1 -name=test \
> +		-time_based -runtime=$runtime &> /dev/null
> +}
> +
> +set_up_test()
> +{
> +	fio -h &> /dev/null || die "fio not found"
> +
> +	# create a simple raid6
> +	mdadm -Cv -R -n 6 -l6 $md0 $devs --assume-clean || die "create raid6
> failed" +
> +	# trigger dirty pages write back
> +	echo 0 > /proc/sys/vm/dirty_background_ratio
> +}
> +
> +clean_up_test()
> +{
> +	echo $old > /proc/sys/vm/dirty_background_ratio
> +
> +	kill -9 $pid
> +	sync $md0
> +
> +	if ! mdadm -S $md0; then
> +		die "can't stop array, deadlock is probably triggered"
> +	fi

Stop is problematic, I described why in previous patch.
You can clean up array manually by ( I think you should to limit complexity):

echo inactive > /sys/block/mdX/md/array_state
echo clear > /sys/block/mdX/md/array_state

Probably, one of those actions will hang right? The question is how we can
catch it.
I'm fine with current approach too:

Acked-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>

Thanks,
Mariusz