linux-kernel - Re: [PATCH] sched: Fix race in rt_mutex_pre_schedule by removing non-atomic fetch_and

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Message-ID: <20250826141659.VMLwv13e@linutronix.de>
Date: Tue, 26 Aug 2025 16:16:59 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: cuiguoqi <cuiguoqi@...inos.cn>, 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>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Clark Williams <clrkwllms@...nel.org>, guoqi0226@....com,
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH] sched: Fix race in rt_mutex_pre_schedule by removing
 non-atomic fetch_and_set

On 2025-08-26 09:56:15 [-0400], Steven Rostedt wrote:
> Honestly, without adding a READ_ONCE() or barrier() I don't see how your
> change would prevent the compiler from making the code any different?

Other than that, that flag is supposed to be only set/ cleared by the
thread itself. There should be no need for it to be atomic.

> It may have "fixed" your issue because the compiler may have done things
> differently, but this change doesn't guarantee anything.
> 
> Also, could you show an example of how current->sched_rt_mutex could be
> corrupted?

That would be important.

> -- Steve

Sebastian