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Date:   Tue, 1 Oct 2019 16:39:22 -0400
From:   Joel Fernandes <joel@joelfernandes.org>
To:     John Stultz <john.stultz@linaro.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Alistair Delva <adelva@google.com>
Subject: Re: [GIT PULL] scheduler fixes
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On Tue, Oct 01, 2019 at 11:15:01AM -0700, John Stultz wrote:
> On Tue, Oct 1, 2019 at 12:19 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Mon, Sep 30, 2019 at 04:45:49PM -0700, John Stultz wrote:
> > > Reverting the following patches:
> >
> > >   "sched/membarrier: Fix p->mm->membarrier_state racy load"
> >
> > ARGH, I fudged it... please try:
> >
> >
> > diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
> > index a39bed2c784f..168479a7d61b 100644
> > --- a/kernel/sched/membarrier.c
> > +++ b/kernel/sched/membarrier.c
> > @@ -174,7 +174,6 @@ static int membarrier_private_expedited(int flags)
> >                  */
> >                 if (cpu == raw_smp_processor_id())
> >                         continue;
> > -               rcu_read_lock();
> >                 p = rcu_dereference(cpu_rq(cpu)->curr);
> >                 if (p && p->mm == mm)
> >                         __cpumask_set_cpu(cpu, tmpmask);
> 
> 
> Yep. Looks like that solves it!
> Tested-by: John Stultz <john.stultz@linaro.org>

Makes sense.

And here I was wondering yesterday why I was seeing bug reports with
t->read_lock_nesting as non-zero when the task was interrupted in user mode ;-)

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>

thanks,

 - Joel