linux-kernel - Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup

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Message-ID: <20180426085719.GW4129@hirez.programming.kicks-ass.net>
Date:   Thu, 26 Apr 2018 10:57:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Gaurav Kohli <gkohli@...eaurora.org>
Cc:     tglx@...utronix.de, mpe@...erman.id.au, mingo@...nel.org,
        bigeasy@...utronix.de, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Will Deacon <will.deacon@....com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against
 wakeup

On Thu, Apr 26, 2018 at 10:41:31AM +0200, Peter Zijlstra wrote:
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index cd50e99202b0..4b6503c6a029 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -177,12 +177,13 @@ void *kthread_probe_data(struct task_struct *task)
>  
>  static void __kthread_parkme(struct kthread *self)
>  {
> -	__set_current_state(TASK_PARKED);
> -	while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
> +	for (;;) {
> +		__set_task_state(TASK_PARKED);

		set_current_state(TASK_PARKED);

of course..

> +		if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
> +			break;
>  		if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
>  			complete(&self->parked);
>  		schedule();
> -		__set_current_state(TASK_PARKED);
>  	}
>  	clear_bit(KTHREAD_IS_PARKED, &self->flags);
>  	__set_current_state(TASK_RUNNING);
>