From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org,
valentin.schneider@arm.com, bristot@redhat.com,
frederic@kernel.org
Subject: Re: lockdep splat in v5.11-rc1 involving console_sem and rq locks
Date: Wed, 6 Jan 2021 06:46:21 -0800 [thread overview]
Message-ID: <20210106144621.GJ17086@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <X/WITr5JuNvuMH+p@hirez.programming.kicks-ass.net>
On Wed, Jan 06, 2021 at 10:52:14AM +0100, Peter Zijlstra wrote:
> On Tue, Jan 05, 2021 at 02:01:15PM -0800, Paul E. McKenney wrote:
> > Hello!
> >
> > The RUDE01 rcutorture scenario (and less often, the TASKS01 scenario)
> > results in occasional lockdep splats on v5.11-rc1 on x86. This failure
> > is probabalistic, sometimes happening as much as 30% of the time, but
> > sometimes happening quite a bit less frequently. (And yes, this did
> > result in a false bisection. Why do you ask?) The problem seems to
> > happen more frequently shortly after boot, so for fastest reproduction
> > run lots of 10-minute RUDE01 runs, which did eventually result in a
> > good bisection. (Yes, I did hammer the last good commit for awhile.)
> >
> > The first bad commit is 1cf12e08bc4d ("sched/hotplug: Consolidate task
> > migration on CPU unplug"). An example splat is shown below.
> >
> > Thoughts?
>
> The splat is because you hit a WARN, we're working on that.
Huh. The WARN does not always generate the lockdep complaint. But
fair enough.
> https://lkml.kernel.org/r/20201226025117.2770-1-jiangshanlai@gmail.com
Thomas pointed me at this one a couple of weeks ago. Here is an
additional fix for rcutorture: f67e04bb0695 ("torture: Break affinity
of kthreads last running on outgoing CPU"). I am still getting WARNs
and lockdep splats with both applied.
What would break if I made the code dump out a few entries in the
runqueue if the warning triggered?
Thanx, Paul
next prev parent reply other threads:[~2021-01-06 14:47 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-05 22:01 lockdep splat in v5.11-rc1 involving console_sem and rq locks Paul E. McKenney
2021-01-06 9:52 ` Peter Zijlstra
2021-01-06 14:46 ` Paul E. McKenney [this message]
2021-01-06 15:44 ` Peter Zijlstra
2021-01-06 15:49 ` Valentin Schneider
2021-01-06 17:52 ` Paul E. McKenney
2021-01-11 14:42 ` Peter Zijlstra
2021-01-11 15:11 ` Paul E. McKenney
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