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From:   Thomas Gleixner <tglx@linutronix.de>
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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
In-Reply-To: <20201207115953.GR3021@hirez.programming.kicks-ass.net>
References: <20201206211253.919834182@linutronix.de> <20201206212002.582579516@linutronix.de> <20201207115953.GR3021@hirez.programming.kicks-ass.net>
Date:   Mon, 07 Dec 2020 18:44:46 +0100
Message-ID: <871rg15x4h.fsf@nanos.tec.linutronix.de>
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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