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From:   John Stultz <john.stultz@linaro.org>
Date:   Tue, 1 Oct 2019 11:15:01 -0700
Message-ID: <CALAqxLUHj8DdiKauwfobS4LzPphhmZdG=GP51zcQMQdmZf=rFg@mail.gmail.com>
Subject: Re: [GIT PULL] scheduler fixes
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     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>,
        Joel Fernandes <joelaf@google.com>,
        Alistair Delva <adelva@google.com>
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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>

Thanks so much for the quick turnaround!
-john