linux-kernel - Re: [RFC PATCH 4/4] Fix: sched/membarrier: p->mm->membarrier

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Message-ID: <839513130.2802.1568394420373.JavaMail.zimbra@efficios.com>
Date:   Fri, 13 Sep 2019 13:07:00 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        paulmck <paulmck@...ux.ibm.com>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Russell King, ARM Linux" <linux@...linux.org.uk>,
        Chris Metcalf <cmetcalf@...hip.com>,
        Chris Lameter <cl@...ux.com>, Kirill Tkhai <tkhai@...dex.ru>,
        Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 4/4] Fix: sched/membarrier: p->mm->membarrier_state
 racy load (v2)



----- On Sep 13, 2019, at 12:04 PM, Oleg Nesterov oleg@...hat.com wrote:

> On 09/13, Mathieu Desnoyers wrote:
>>
>> membarrier_exec_mmap(), which seems to be affected by the same problem.
> 
> IIRC, in the last version it is called by exec_mmap() undef task_lock(),
> so it should fine.

Fair point. Although it seems rather cleaner to use this_cpu_write() in
all 3 sites updating this variable rather than a mix of this_cpu_write
and WRITE_ONCE(), unless anyone objects.

Thanks,

Mathieu


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