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Date:   Tue, 15 Aug 2023 18:15:57 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     bigeasy@linutronix.de, tglx@linutronix.de
Cc:     linux-kernel@vger.kernel.org, bsegall@google.com,
        boqun.feng@gmail.com, swood@redhat.com, bristot@redhat.com,
        dietmar.eggemann@arm.com, mingo@redhat.com, jstultz@google.com,
        juri.lelli@redhat.com, mgorman@suse.de, rostedt@goodmis.org,
        vschneid@redhat.com, vincent.guittot@linaro.org,
        longman@redhat.com, will@kernel.org
Subject: Re: [PATCH 0/6] locking/rtmutex: Avoid PI state recursion through
 sched_submit_work()
Message-ID: <20230815161557.GK214207@hirez.programming.kicks-ass.net>
References: <20230815110121.117752409@infradead.org>
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On Tue, Aug 15, 2023 at 01:01:21PM +0200, Peter Zijlstra wrote:
> Hi!
> 
> This is basically the 'same' patches as send earlier by Sebastian here:
> 
>   https://lkml.kernel.org/r/20230427111937.2745231-1-bigeasy@linutronix.de
> 
> I spend a number of days trying to invert rtmutex, only to make a giant mess of
> things and finally conceded that this is the least horrible approach.
> 
> There's a bunch of naming differences and I added some asserts that should
> hopefully avoid things from going sideways without notice. I've also updated
> the changelogs to high-light the actual problem. The whole pi_blocked_on
> 'corruption' is a mere consequence of the more fundamental problem that the
> whole PI state recurses.
> 
> I've not tested this with the rest of the RT patches stuck on, so very limited
> actual testing happened.
> 
> If anybody could please confirm stuff still works as advertised, I'll go queue
> this mess and we can hopefully forget all about it.
> 

N/m - 0day found a problem. Futex-PI trips the rt_mutex_schedule()
assertion for not passing through rt_mutex_pre_schedule().

I'll go try and untangle that...