linux-kernel - Re: [PATCH 7/8] kernel/fork: Only cache the VMAP stack in finish_task

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Message-ID: <YgqV1BLbCx5V+6tq@linutronix.de>
Date:   Mon, 14 Feb 2022 18:48:04 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH 7/8] kernel/fork: Only cache the VMAP stack in
 finish_task_switch().

On 2022-02-14 17:54:48 [+0100], To Andy Lutomirski wrote:
> index fcf0c180617c2..defe31036930a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4895,8 +4895,11 @@ static struct rq *finish_task_switch(struct task_struct *prev)
>  		if (prev->sched_class->task_dead)
>  			prev->sched_class->task_dead(prev);
>  
> -		/* Task is done with its stack. */
> -		put_task_stack(prev);
> +		/*
> +		 * Task is done with its stack. Try to cache VMAP stack and
> +		 * delay free it otherwise.
> +		 */
> +		put_task_stack_sched(prev);

Now that I write the commit message, there is probably nothing wrong
with unconditionally delaying it via RCU if caching failed. Then I don't
have to explain that there is one function is for the atomic context and
the other for non-atomic.

>  		put_task_struct_rcu_user(prev);
>  	}
> -- 
Sebastian