linux-kernel - Re: [PATCH v23 2/9] sched: Fix modifying donor->blocked on without proper locking

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Message-ID: <84c4aa9d-9094-4b12-8912-63a338a43351@amd.com>
Date: Thu, 30 Oct 2025 10:21:00 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: John Stultz <jstultz@...gle.com>, LKML <linux-kernel@...r.kernel.org>
CC: Joel Fernandes <joelagnelf@...dia.com>, Qais Yousef <qyousef@...alina.io>,
	Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, "Juri
 Lelli" <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>, Valentin Schneider
	<vschneid@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, Ben Segall
	<bsegall@...gle.com>, Zimuzo Ezeozue <zezeozue@...gle.com>, Mel Gorman
	<mgorman@...e.de>, Will Deacon <will@...nel.org>, Waiman Long
	<longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>, "Paul E. McKenney"
	<paulmck@...nel.org>, Metin Kaya <Metin.Kaya@....com>, Xuewen Yan
	<xuewen.yan94@...il.com>, Thomas Gleixner <tglx@...utronix.de>, "Daniel
 Lezcano" <daniel.lezcano@...aro.org>, Suleiman Souhlal <suleiman@...gle.com>,
	kuyo chang <kuyo.chang@...iatek.com>, hupu <hupu.gm@...il.com>,
	<kernel-team@...roid.com>
Subject: Re: [PATCH v23 2/9] sched: Fix modifying donor->blocked on without
 proper locking

Hello John,

On 10/30/2025 5:48 AM, John Stultz wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 517b26c515bc5..0533a14ce5935 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6591,7 +6591,7 @@ static struct task_struct *proxy_deactivate(struct rq *rq, struct task_struct *d
>  		 * as unblocked, as we aren't doing proxy-migrations
>  		 * yet (more logic will be needed then).
>  		 */
> -		donor->blocked_on = NULL;
> +		clear_task_blocked_on(donor, NULL);

nit. You can probably switch this to use __clear_task_blocked_on() in
the previous patch and then to the clear_task_blocked_on() variant here.
It makes it more clear that proxy_deactivate() is now out of the
"donor->blocked_lock" critical section.

Either way, no strong feelings.

>  	}
>  	return NULL;
>  }
> @@ -6619,6 +6619,7 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
>  	int this_cpu = cpu_of(rq);
>  	struct task_struct *p;
>  	struct mutex *mutex;
> +	enum { FOUND, DEACTIVATE_DONOR } action = FOUND;

nit. If you move that declaration to the top, you can preserve the nice
reverse xmas arrangement ;)

Apart from those couple of nits, feel free to include:

Reviewed-by: K Prateek Nayak <kprateek.nayak@....com>

-- 
Thanks and Regards,
Prateek