[PATCH v2 0/1] dm-delay: fix hung task issue

From: Joel Colledge
Date: Mon May 06 2024 - 03:26:16 EST


Hi,

The tests for DRBD encountered an issue with dm-delay when testing with
a 6.8 series kernel. Specifically on Ubuntu 24.04 "Noble". Here is a
minimal reproducer:

virter vm run --name dm-delay-test --id 10 --wait-ssh ubuntu-noble
virter vm ssh dm-delay-test
# truncate -s 100M /file
# loop_dev=$(losetup -f --show /file)
# echo "0 $(blockdev --getsz $loop_dev) delay $loop_dev 0 0" | dmsetup create delay-volume

After a few minutes, the following is printed to the kernel log:

[ 246.919123] INFO: task dm-delay-flush-:1256 blocked for more than 122 seconds.
[ 246.922543] Not tainted 6.8.0-31-generic #31-Ubuntu
[ 246.923753] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 246.924932] task:dm-delay-flush- state:D stack:0 pid:1256 tgid:1256 ppid:2 flags:0x00004000
[ 246.924940] Call Trace:
[ 246.924950] <TASK>
[ 246.924980] __schedule+0x27c/0x6b0
[ 246.925002] ? __pfx_flush_worker_fn+0x10/0x10 [dm_delay]
[ 246.925011] schedule+0x33/0x110
[ 246.925016] schedule_preempt_disabled+0x15/0x30
[ 246.925035] kthread+0xb1/0x120
..

This bug appears to have been introduced in Linux v6.7.

The following patch fixes the issue.

Thanks Christian and Benjamin for the comments on v1!

Changes from v1:
- Use kthread_run() instead of wake_up_process()

Joel Colledge (1):
dm-delay: fix hung task introduced by kthread mode

drivers/md/dm-delay.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

--
2.34.1