linux-kernel - Re: [PATCH] Fix: membarrier: add missing preempt off around smp_call_function

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Date:   Wed, 20 Dec 2017 15:02:56 +0000 (UTC)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andrew Hunter <ahh@...gle.com>,
        maged michael <maged.michael@...il.com>,
        Avi Kivity <avi@...lladb.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Dave Watson <davejwatson@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrea Parri <parri.andrea@...il.com>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] Fix: membarrier: add missing preempt off around
 smp_call_function_many

Hi Linus, Peter, Ingo,

Now that membarrier.c has been moved from kernel/ to kernel/sched/, should
I route this membarrier fix through the scheduler maintainers, or is it OK
to send it to you directly ?

Thanks,

Mathieu

----- On Dec 15, 2017, at 2:23 PM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:

> smp_call_function_many requires disabling preemption around the call.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Peter Zijlstra <peterz@...radead.org>
> CC: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> CC: Boqun Feng <boqun.feng@...il.com>
> CC: Andrew Hunter <ahh@...gle.com>
> CC: Maged Michael <maged.michael@...il.com>
> CC: Avi Kivity <avi@...lladb.com>
> CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> CC: Paul Mackerras <paulus@...ba.org>
> CC: Michael Ellerman <mpe@...erman.id.au>
> CC: Dave Watson <davejwatson@...com>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: Andrea Parri <parri.andrea@...il.com>
> CC: <stable@...r.kernel.org>	# v4.14
> ---
> kernel/sched/membarrier.c | 2 ++
> 1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
> index dd7908743dab..9bcbacba82a8 100644
> --- a/kernel/sched/membarrier.c
> +++ b/kernel/sched/membarrier.c
> @@ -89,7 +89,9 @@ static int membarrier_private_expedited(void)
> 		rcu_read_unlock();
> 	}
> 	if (!fallback) {
> +		preempt_disable();
> 		smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
> +		preempt_enable();
> 		free_cpumask_var(tmpmask);
> 	}
> 	cpus_read_unlock();
> --
> 2.11.0

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com