linux-kernel - Re: sched: Reenable interrupts in do sched

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Message-ID: <87o8kw93n4.fsf@nanos.tec.linutronix.de>
Date:   Tue, 20 Oct 2020 20:02:55 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: sched: Reenable interrupts in do sched_yield()

On Tue, Oct 20 2020 at 11:38, Steven Rostedt wrote:
> On Tue, 20 Oct 2020 16:46:55 +0200
> Thomas Gleixner <tglx@...utronix.de> wrote:
>
>> -	/*
>> -	 * Since we are going to call schedule() anyway, there's
>> -	 * no need to preempt or enable interrupts:
>
> I think the above comment still makes sense, just needs to be tweeked:
>
> 	/*
> 	 * Since we are going to call schedule() anyway, there's
> 	 * no need to allow preemption after releasing the rq lock.
>> -	 */
>
> Especially, since we are now enabling interrupts, which is likely to
> trigger a preemption.

sched_preempt_enable_no_resched() still enables preemption. It just
avoids the check. And it still allows preemption when an interrupt
triggering preemption happens between sched_preempt_enable_no_resched()
and __schedule() disabling preemption/interrupts.

So no, your new variant is just differently bogus and misleading.

Thanks,

        tglx