Re: Pausing md check hangs

[Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx>]

On 3/10/20 4:30 PM, Georgi Nikolov wrote:
> I have tried new 4.19 kernel with proposed patches with no success. Same story with md1_raid6 (last 
> time it was with 5.4 and md10_raid6).

Did "cat /sys/block/mdX/md/journal_mode" still hang? I thought below change would help ...
> > diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
> > index 9b6da759dca2..a961d8eed73e 100644
> > --- a/drivers/md/raid5-cache.c
> > +++ b/drivers/md/raid5-cache.c
> > @@ -2532,13 +2532,10 @@ static ssize_t r5c_journal_mode_show(struct mddev *mddev, char *page)
> >         struct r5conf *conf;
> >         int ret;
> >
> > -       ret = mddev_lock(mddev);
> > -       if (ret)
> > -               return ret;
> > -
> > +       spin_lock(&mddev->lock);
> >         conf = mddev->private;
> >         if (!conf || !conf->log) {
> > -               mddev_unlock(mddev);
> > +               spin_unlock(&mddev->lock);
> >                 return 0;
> >         }
> >
> > @@ -2558,7 +2555,7 @@ static ssize_t r5c_journal_mode_show(struct mddev *mddev, char *page)
> >         default:
> >                 ret = 0;
> >         }
> > -       mddev_unlock(mddev);
> > +       spin_unlock(&mddev->lock);
> >         return ret;
> >  }


Could you try with remove flush_workqueue(md_misc_wq) from below change? Or add some debug infos to 
see whether the hang is caused by flush_workqueue.

> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -4779,7 +4779,8 @@ action_store(struct mddev *mddev, const char *page, size_t len)
> >                 if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
> >                     mddev_lock(mddev) == 0) {
> >                         flush_workqueue(md_misc_wq);
> > -                       if (mddev->sync_thread) {
> > +                       if (mddev->sync_thread ||
> > + test_bit(MD_RECOVERY_RUNNING,&mddev->recovery)) {

Thanks,
Guoqing