linux-kernel - Re: [PATCH] sched/core: Fix a missed update of user_cpus

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Message-ID: <Y+pPoOxuYtq+GBbA@hirez.programming.kicks-ass.net>
Date:   Mon, 13 Feb 2023 15:56:32 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Will Deacon <will@...nel.org>, Phil Auld <pauld@...hat.com>,
        Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/core: Fix a missed update of user_cpus_ptr

On Fri, Feb 03, 2023 at 01:18:49PM -0500, Waiman Long wrote:
> Since commit 8f9ea86fdf99 ("sched: Always preserve the user requested
> cpumask"), a successful call to sched_setaffinity() should always save
> the user requested cpu affinity mask in a task's user_cpus_ptr. However,
> when the given cpu mask is the same as the current one, user_cpus_ptr
> is not updated. Fix this by saving the user mask in this case too.
> 
> Fixes: 8f9ea86fdf99 ("sched: Always preserve the user requested cpumask")
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  kernel/sched/core.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 30d9752e2ca5..91255f791df3 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2951,8 +2951,11 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
>  	}
>  
>  	if (!(ctx->flags & SCA_MIGRATE_ENABLE)) {
> -		if (cpumask_equal(&p->cpus_mask, ctx->new_mask))
> +		if (cpumask_equal(&p->cpus_mask, ctx->new_mask)) {
> +			if (ctx->flags & SCA_USER)
> +				swap(p->user_cpus_ptr, ctx->user_mask);
>  			goto out;
> +		}
>  
>  		if (WARN_ON_ONCE(p == current &&
>  				 is_migration_disabled(p) &&

Indeed. Thanks!