Re: Infiniate systemd loop when power off the machine with multiple MD RAIDs

[Yu Kuai <yukuai1@huaweicloud.com>]

Hi,

在 2023/08/23 3:13, Carlos Carvalho 写道:
> Song Liu (song@kernel.org) wrote on Tue, Aug 22, 2023 at 03:56:04PM -03:
>> >From systemd code, i.e. function delete_md(), this error:
>>
>> [ 205.957004] systemd-shutdown[1]: Stopping MD /dev/md124p1 (259:6).
>> [ 205.964177] systemd-shutdown[1]: Could not stop MD /dev/md124p1:
>> Device or resource busy
>>
>> is most likely triggered by ioctl(STOP_ARRAY).
>>
>> And based on the code, I think the ioctl fails here:
>>
>>          if (cmd == STOP_ARRAY || cmd == STOP_ARRAY_RO) {
>>                  /* Need to flush page cache, and ensure no-one else opens
>>                   * and writes
>>                   */
>>                  mutex_lock(&mddev->open_mutex);
>>                  if (mddev->pers && atomic_read(&mddev->openers) > 1) {
>>                          mutex_unlock(&mddev->open_mutex);
>>                          err = -EBUSY;
>>                          goto out;        ////////////////////// HERE

Yes, I suspect here as well, but I do some test with error injection to
gurantee that ioctl(STOP_ARRAY) always return -EBUSY, but I found that
system reboot didn't hang, it'll try a few times but eventually reboot
finished.

>>                  }
>>                  if (test_and_set_bit(MD_CLOSING, &mddev->flags)) {
>>                          mutex_unlock(&mddev->open_mutex);
>>                          err = -EBUSY;
>>                          goto out;
>>                  }
>>                  did_set_md_closing = true;
>>                  mutex_unlock(&mddev->open_mutex);
>>                  sync_blockdev(bdev);
>>          }
> 
> Probably. The problem is why doesn't it manage to flush the page cache? I find
> strange that the problem appears only when trying to stop the array, I get it
> when trying to umount the filesystem, where it also hangs because of the same
> reason. The kworker thread runs continuously using 100% cpu of only 1 core.

The kworker do you mean the daemon thread or the sync thread?  runs
continuously using 100% cpu doen't sounds correct to me.

Thanks,
Kuai

> 
> These are all similar symptoms of the underlying problem which I complained
> about days ago: the system doesn't manage to write to the disks, which stay
> nearly idle. If you wait long enough without issuing writes, which can be
> several hours, it'll eventually flush the page cache and proceed to a "normal"
> umount or reboot.
> 
> The bug is dependent on the rate of writes and also on uptime; it rarely
> appears soon after boot, and increases as times passes.
> 
> .
>