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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: sched: Reenable interrupts in do sched_yield()
In-Reply-To: <20201020113830.378b4a4c@gandalf.local.home>
References: <87r1pt7y5c.fsf@nanos.tec.linutronix.de> <20201020113830.378b4a4c@gandalf.local.home>
Date:   Tue, 20 Oct 2020 20:02:55 +0200
Message-ID: <87o8kw93n4.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
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On Tue, Oct 20 2020 at 11:38, Steven Rostedt wrote:
> On Tue, 20 Oct 2020 16:46:55 +0200
> Thomas Gleixner <tglx@linutronix.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