linux-kernel - Re: [PATCH] sched/rt: Fix double enqueue caused by rt_effective

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Date:   Thu, 8 Jul 2021 13:35:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        dietmar.eggemann@....com, bristot@...hat.com, bsegall@...gle.com,
        mgorman@...e.de, Mark Simmons <msimmons@...hat.com>
Subject: Re: [PATCH] sched/rt: Fix double enqueue caused by rt_effective_prio

On Thu, Jul 01, 2021 at 11:14:31AM +0200, Juri Lelli wrote:
> Looks like this survives the test case (and regression testing), but I'm
> still not fully convinced that the above statement "Concurrent priority
> inheritance handling is still safe and will eventually converge to a new
> state by following the inheritance chain(s)" is actually sound.

I think we good there. rt_mutex_adjust_prio_chain() updates ->prio in
step 7 and calls rt_mutex_setprio() in step 11.

So if we race against __sched_setschedule() and observe the old value,
step 11 will follow up and correct us.