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

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Message-ID: <20201207223853.GL2657@paulmck-ThinkPad-P72>
Date:   Mon, 7 Dec 2020 14:38:53 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Marco Elver <elver@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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 Mon, Dec 07, 2020 at 10:46:33PM +0100, Thomas Gleixner wrote:
> On Mon, Dec 07 2020 at 11:44, Paul E. McKenney wrote:
> > On Mon, Dec 07, 2020 at 07:19:51PM +0100, Marco Elver wrote:
> >> On Mon, 7 Dec 2020 at 18:46, Thomas Gleixner <tglx@...utronix.de> wrote:
> >> I currently don't know what the rule for Peter's preferred variant
> >> would be, without running the risk of some accidentally data_race()'d
> >> accesses.
> >> 
> >> Thoughts?
> >
> > I am also concerned about inadvertently covering code with data_race().
> >
> > 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()?
> 
> That was your suggestion a week or so ago :)

You expected my suggestion to change?  ;-)

							Thanx, Paul