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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Marco Elver <elver@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	Ingo Molnar <mingo@kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Will Deacon <will@kernel.org>,
	Naresh Kamboju <naresh.kamboju@linaro.org>,
	syzbot+23a256029191772c2f02@syzkaller.appspotmail.com,
	syzbot+56078ac0b9071335a745@syzkaller.appspotmail.com,
	syzbot+867130cb240c41f15164@syzkaller.appspotmail.com
Subject: Re: [patch 3/3] tick: Annotate tick_do_timer_cpu data races
Date: Mon, 7 Dec 2020 14:55:42 -0800	[thread overview]
Message-ID: <20201207225542.GM2657@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <878sa944kn.fsf@nanos.tec.linutronix.de>

On Mon, Dec 07, 2020 at 11:46:48PM +0100, Thomas Gleixner wrote:
> On Mon, Dec 07 2020 at 14:38, Paul E. McKenney wrote:
> 
> > 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@linutronix.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?  ;-)
> 
> Your suggestion was data_race() IIRC but I might have lost track in that
> conversation.

OK, I am inconsistent after all.  I would have suggested READ_ONCE() given
no difference between them, so it is probably best to assume that there is
(or at least was) a good reason for data_race() instead of READ_ONCE().
Couldn't tell you what it might be, though.  :-/

							Thanx, Paul

  reply	other threads:[~2020-12-07 22:56 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-06 21:12 [patch 0/3] tick: Annotate and document the intentionaly racy tick_do_timer_cpu Thomas Gleixner
2020-12-06 21:12 ` [patch 1/3] tick: Remove pointless cpu valid check in hotplug code Thomas Gleixner
2020-12-07 11:59   ` Peter Zijlstra
2020-12-07 17:44     ` Thomas Gleixner
2020-12-11 22:21   ` Frederic Weisbecker
2020-12-12  0:16     ` Thomas Gleixner
2020-12-12  1:20       ` Frederic Weisbecker
2020-12-11 22:31   ` Frederic Weisbecker
2020-12-16 10:50   ` [tip: timers/urgent] " tip-bot2 for Thomas Gleixner
2020-12-06 21:12 ` [patch 2/3] tick/sched: Remove bogus boot "safety" check Thomas Gleixner
2020-12-11 22:41   ` Frederic Weisbecker
2020-12-16 10:50   ` [tip: timers/urgent] " tip-bot2 for Thomas Gleixner
2020-12-06 21:12 ` [patch 3/3] tick: Annotate tick_do_timer_cpu data races Thomas Gleixner
2020-12-07 12:09   ` Peter Zijlstra
2020-12-07 17:46     ` Thomas Gleixner
2020-12-07 18:19       ` Marco Elver
2020-12-07 19:43         ` Thomas Gleixner
2020-12-07 19:44         ` Paul E. McKenney
2020-12-07 21:46           ` Thomas Gleixner
2020-12-07 22:38             ` Paul E. McKenney
2020-12-07 22:46               ` Thomas Gleixner
2020-12-07 22:55                 ` Paul E. McKenney [this message]
2020-12-08  8:11           ` Peter Zijlstra
2020-12-08 15:03             ` Paul E. McKenney
2020-12-16  0:27               ` Thomas Gleixner
2020-12-16 21:19                 ` Paul E. McKenney
2020-12-16 21:23                   ` Thomas Gleixner
2020-12-16 21:32                     ` Paul E. McKenney
2020-12-17 10:48                   ` Peter Zijlstra
2020-12-17 14:59                     ` Paul E. McKenney
2020-12-08  8:01         ` Peter Zijlstra
2020-12-07 11:05 ` [patch 0/3] tick: Annotate and document the intentionaly racy tick_do_timer_cpu Marco Elver

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