linux-kernel - Re: [PATCH RT 1/8] sched: migrate_enable: Use sleeping

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Message-ID: <20190729092653.20bcc45e@gandalf.local.home>
Date:   Mon, 29 Jul 2019 09:26:53 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Scott Wood <swood@...hat.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Clark Williams <williams@...hat.com>,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH RT 1/8] sched: migrate_enable: Use sleeping_lock to
 indicate involuntary sleep

On Sat, 27 Jul 2019 00:56:31 -0500
Scott Wood <swood@...hat.com> wrote:

> Without this, rcu_note_context_switch() will complain if an RCU read
> lock is held when migrate_enable() calls stop_one_cpu().
> 
> Signed-off-by: Scott Wood <swood@...hat.com>
>

> index d3c6542b306f..c3407707e367 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7405,7 +7405,9 @@ void migrate_enable(void)
>  			unpin_current_cpu();
>  			preempt_lazy_enable();
>  			preempt_enable();

This looks like it needs a comment to explain why this is.

-- Steve

> +			sleeping_lock_inc();
>  			stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
> +			sleeping_lock_dec();
>  			return;
>  		}
>  	}