linux-kernel - Re: [patch 3/3] tick: Annotate tick_do_timer

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Message-ID: <87czz9savm.fsf@nanos.tec.linutronix.de>
Date:   Wed, 16 Dec 2020 22:23:57 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     paulmck@...nel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Marco Elver <elver@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Ingo Molnar <mingo@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Will Deacon <will@...nel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        syzbot+23a256029191772c2f02@...kaller.appspotmail.com,
        syzbot+56078ac0b9071335a745@...kaller.appspotmail.com,
        syzbot+867130cb240c41f15164@...kaller.appspotmail.com
Subject: Re: [patch 3/3] tick: Annotate tick_do_timer_cpu data races

On Wed, Dec 16 2020 at 13:19, Paul E. McKenney wrote:
> On Wed, Dec 16, 2020 at 01:27:43AM +0100, Thomas Gleixner wrote:
>> So my intent was to document that this code does not care about anything
>> else than what I'd consider to be plain compiler bugs.
>> 
>> My conclusion might be wrong as usual :)
>
> Given that there is no optimization potential, then the main reason to use
> data_race() instead of *_ONCE() is to prevent KCSAN from considering the
> accesses when looking for data races.  But that is mostly for debugging
> accesses, in cases when these accesses are not really part of the
> concurrent algorithm.
>
> So if I understand the situation correctly, I would be using *ONCE().

Could this be spelled out somewhere in Documentation/ please?

Thanks,

        tglx