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

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Message-ID: <1285036359.17389.1568914389549.JavaMail.zimbra@efficios.com>
Date:   Thu, 19 Sep 2019 13:33:09 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Will Deacon <will@...nel.org>
Cc:     Michael Kerrisk <mtk.manpages@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        paulmck <paulmck@...ux.ibm.com>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "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 19, 2019, at 12:26 PM, Will Deacon will@...nel.org wrote:

[...]
>> 
>> The current wording from membarrier(2) is:
>> 
>>               The  "expedited" commands complete faster than the non-expedited
>>               ones; they never block, but have the downside of  causing  extra
>>               overhead.
>> 
>> We could simply remove the "; they never block" part then ?
> 
> I think so, yes. That or, "; they do not voluntarily block" or something
> like that. Maybe look at other man pages for inspiration ;)

OK, let's tackle the man-pages part after the fix reaches mainline though.

[...]
> 
> I reckon you'll be fine using GFP_KERNEL and returning -ENOMEM on allocation
> failure. This shouldn't happen in practice and it removes the fallback
> path.

Works for me! I'll prepare an updated patchset.

Thanks,

Mathieu


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