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From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Marco Elver <elver@google.com>,
	kasan-dev <kasan-dev@googlegroups.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Will Deacon <will@kernel.org>,
	Naresh Kamboju <naresh.kamboju@linaro.org>
Subject: Re: [patch 1/3] tick: Remove pointless cpu valid check in hotplug code
Date: Mon, 07 Dec 2020 18:44:46 +0100	[thread overview]
Message-ID: <871rg15x4h.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201207115953.GR3021@hirez.programming.kicks-ass.net>

On Mon, Dec 07 2020 at 12:59, Peter Zijlstra wrote:
> On Sun, Dec 06, 2020 at 10:12:54PM +0100, Thomas Gleixner wrote:
>
>>  void tick_handover_do_timer(void)
>>  {
>> +	if (tick_do_timer_cpu == smp_processor_id())
>> +		tick_do_timer_cpu = cpumask_first(cpu_online_mask);
>
> For the paranoid amongst us, would it make sense to add something like:
>
> 	/*
> 	 * There must always be at least one online CPU.
> 	 */
> 	WARN_ON_ONCE(tick_do_timer_cpu >= nr_cpu_ids);

And add that to all places which look at online mask during hotplug.

If we really care we can add it somewhere central in the hotplug
code. If that ever triggers then the wreckaged tick duty is just
uninteresting.

Thanks,

        tglx

  reply	other threads:[~2020-12-07 17:45 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 [this message]
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
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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