Comment 10 for bug 1942935

The patch hasn't made it into mainline from what I have seen, it looks like it died back in March waiting for feedback from additional kernel developers. From what I have gathered this is a deadlock scenario directly caused by pausing the resync while the system is under heavy write activity.

Donald Buczek provided a reproducer which is a shell script that generates a lot of write activity and pauses/resumes the raid scrubbing. And he also provided a workaround to get the stuck system running without reboot:

echo active > /sys/block/md1/md/array_state

I haven't tried the patch or any of this, I pretty much eliminated the trigger which is mdcheck_start & mdcheck_continue and went back to the 18.04 LTS way of scrubbing arrays (which is basically don't pause/interrupt it once it starts). I ran through a checkarray yesterday to 100%, no problems. Meanwhile since upgrading to 20.04 LTS it has hung almost every single time through 5.4, 5.8, and 5.11 kernels.