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

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Message-ID: <20201208150309.GP2657@paulmck-ThinkPad-P72>
Date:   Tue, 8 Dec 2020 07:03:09 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Marco Elver <elver@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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 Tue, Dec 08, 2020 at 09:11:29AM +0100, Peter Zijlstra wrote:
> On Mon, Dec 07, 2020 at 11:44:06AM -0800, Paul E. McKenney wrote:
> 
> > Also, in this particular case, why data_race() rather than READ_ONCE()?
> > Do we really expect the compiler to be able to optimize this case
> > significantly without READ_ONCE()?
> 
> It's about intent and how the code reads. READ_ONCE() is something
> completely different from data_race(). data_race() is correct here.

Why?

							Thanx, Paul