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Re: BUG_ON in rcu_sync_func triggered

From Oleg Nesterov <oleg@redhat.com>
Newsgroups linux.kernel
Subject Re: BUG_ON in rcu_sync_func triggered
Date 2016-09-23 16:00 +0200
Message-ID <skzbb-4lr-13@gated-at.bofh.it> (permalink)
References (5 earlier) <sgX2p-39g-9@gated-at.bofh.it> <sgXOO-3H6-33@gated-at.bofh.it> <shc1s-5IS-19@gated-at.bofh.it> <shhXc-ZP-21@gated-at.bofh.it> <skyRQ-4e3-31@gated-at.bofh.it>
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On 09/23, Nikolay Borisov wrote:
>
> > --- a/fs/super.c
> > +++ b/fs/super.c
> > @@ -1344,7 +1344,9 @@ int thaw_super(struct super_block *sb)
> >         int error;
> >
> >         down_write(&sb->s_umount);
> > -       if (sb->s_writers.frozen == SB_UNFROZEN) {
> > +       if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
> > +               if (sb->s_writers.frozen != SB_UNFROZEN)
> > +                       pr_crit("THAW: hit the race: %d\n", sb->s_writers.frozen);
> >                 up_write(&sb->s_umount);
> >                 return -EINVAL;
> >         }
> >
> 
> I was away on holiday so that's why I was silent. However, with this
> patch applied I couldn't reproduce the issue nor the pr_crit
> triggered.

Great, thanks a lot.

> Have you had any moments of epiphany re. this issue?

Well, after I failed to find any problem in rcu/sync.c I started to
look at the callers and found this race.

> Should
> some FS people be involved in the discussion?

Sure. I'll send the patch with CC's. Probably next week, I am too
busy right now.

Thanks Nikolay,

Oleg.

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Thread

Re: BUG_ON in rcu_sync_func triggered Oleg Nesterov <oleg@redhat.com> - 2016-09-12 15:10 +0200
  Re: BUG_ON in rcu_sync_func triggered Nikolay Borisov <kernel@kyup.com> - 2016-09-13 10:30 +0200
    Re: BUG_ON in rcu_sync_func triggered Oleg Nesterov <oleg@redhat.com> - 2016-09-13 15:20 +0200
      Re: BUG_ON in rcu_sync_func triggered Oleg Nesterov <oleg@redhat.com> - 2016-09-13 15:50 +0200
        Re: BUG_ON in rcu_sync_func triggered Nikolay Borisov <kernel@kyup.com> - 2016-09-13 16:40 +0200
          Re: BUG_ON in rcu_sync_func triggered Oleg Nesterov <oleg@redhat.com> - 2016-09-13 17:30 +0200
            Re: BUG_ON in rcu_sync_func triggered Nikolay Borisov <kernel@kyup.com> - 2016-09-14 08:40 +0200
              Re: BUG_ON in rcu_sync_func triggered Oleg Nesterov <oleg@redhat.com> - 2016-09-14 15:00 +0200
                Re: BUG_ON in rcu_sync_func triggered Nikolay Borisov <kernel@kyup.com> - 2016-09-23 15:40 +0200
                Re: BUG_ON in rcu_sync_func triggered Oleg Nesterov <oleg@redhat.com> - 2016-09-23 16:00 +0200
          Re: BUG_ON in rcu_sync_func triggered Nikolay Borisov <n.borisov@siteground.com> - 2016-09-13 17:40 +0200
        Re: BUG_ON in rcu_sync_func triggered Nikolay Borisov <kernel@kyup.com> - 2016-09-13 16:40 +0200

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