linux-kernel - Re: [PATCH v3 7/7] locking/rtmutex: Acquire the hb lock via trylock after wait-proxylock.

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Date: Mon, 15 Jan 2024 13:16:32 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	boqun.feng@...il.com, bristot@...hat.com, bsegall@...gle.com,
	dietmar.eggemann@....com, jstultz@...gle.com, juri.lelli@...hat.com,
	longman@...hat.com, mgorman@...e.de, mingo@...hat.com,
	rostedt@...dmis.org, swood@...hat.com, vincent.guittot@...aro.org,
	vschneid@...hat.com, will@...nel.org
Subject: Re: [PATCH v3 7/7] locking/rtmutex: Acquire the hb lock via trylock
 after wait-proxylock.

On 2024-01-15 12:52:49 [+0100], Jiri Slaby wrote:
…
> > 
> > The child in fact terminates on
> > https://github.com/apache/apr/blob/trunk/test/testprocmutex.c#L93:
> >                  while ((rv = apr_proc_mutex_timedlock(proc_lock, 1))) {
> >                      if (!APR_STATUS_IS_TIMEUP(rv))
> >                          exit(1); <----- here
> > 
> > The test creates 6 children and does some
> > pthread_mutex_timedlock/unlock() repeatedly (200 times) in parallel
> > while sleeping 1 us inside the lock. The timeout is 1 us above. And the
> > test expects all them to fail (to time out). But the time out does not
> > always happen in 6.7 (it's racy, so the failure is semi-random: like 1
> > of 1000 attempts is bad).
> 
> This is not precise as I misinterpreted. The test is: either it succeeds or
> times out.
> 
> But since the commit, futex() yields 22/EINVAL, i.e. fails.

Let me see if I can reproduce it here…

Sebastian