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Date: Mon, 15 Jan 2024 13:16:32 +0100
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Jiri Slaby <jirislaby@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
	boqun.feng@gmail.com, bristot@redhat.com, bsegall@google.com,
	dietmar.eggemann@arm.com, jstultz@google.com, juri.lelli@redhat.com,
	longman@redhat.com, mgorman@suse.de, mingo@redhat.com,
	rostedt@goodmis.org, swood@redhat.com, vincent.guittot@linaro.org,
	vschneid@redhat.com, will@kernel.org
Subject: Re: [PATCH v3 7/7] locking/rtmutex: Acquire the hb lock via trylock
 after wait-proxylock.
Message-ID: <20240115121632.FX1P0-fi@linutronix.de>
References: <20230908162254.999499-1-bigeasy@linutronix.de>
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 <20230911141135.GB9098@noisy.programming.kicks-ass.net>
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On 2024-01-15 12:52:49 [+0100], Jiri Slaby wrote:
=E2=80=A6
> >=20
> > The child in fact terminates on
> > https://github.com/apache/apr/blob/trunk/test/testprocmutex.c#L93:
> >  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 while ((rv =3D apr_proc_mutex_timedlock(proc_lock, 1)=
)) {
> >  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!APR_STATUS_IS_TIMEUP(rv))
> >  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 exit(=
1); <----- here
> >=20
> > 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).
>=20
> This is not precise as I misinterpreted. The test is: either it succeeds =
or
> times out.
>=20
> But since the commit, futex() yields 22/EINVAL, i.e. fails.

Let me see if I can reproduce it here=E2=80=A6

Sebastian