linux-kernel - Re: [PATCH 01/11] sched: Trigger warning if ->migration

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Date:   Thu, 2 Dec 2021 22:02:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ben Segall <bsegall@...gle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Waiman Long <longman@...hat.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH 01/11] sched: Trigger warning if ->migration_disabled
 counter underflows.

On Mon, Nov 29, 2021 at 06:46:44PM +0100, Sebastian Andrzej Siewior wrote:
> If migrate_enable() is used more often than its counter part then it
> remains undetected and rq::nr_pinned will underflow, too.
> 
> Add a warning if migrate_enable() is attempted if without a matching a
> migrate_disable().
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  kernel/sched/core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 76f9deeaa9420..02be3f6144e97 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2171,6 +2171,8 @@ void migrate_enable(void)
>  	if (p->migration_disabled > 1) {
>  		p->migration_disabled--;
>  		return;

Due to return there ^

> +	} else if (WARN_ON_ONCE(p->migration_disabled == 0)) {
> +		return;
>  	}

we can do away with else and simply write:

	if (WARN_ON_ONCE(!p->migration_disabled))
		return;