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

From: Yu Kuai <redacted>

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 (local)
[2]
https://lore.kernel.org/linux-raid/20220621031129.24778-1-guoqing.jiang@linux.dev/ (local)
[3]
https://lore.kernel.org/linux-raid/20230322064122.2384589-5-yukuai1@huaweicloud.com/ (local)

Signed-off-by: Yu Kuai <redacted>
---
 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