linux-kernel - Re: lockdep splat in v5.11-rc1 involving console

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Message-ID: <X/WITr5JuNvuMH+p@hirez.programming.kicks-ass.net>
Date:   Wed, 6 Jan 2021 10:52:14 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        valentin.schneider@....com, bristot@...hat.com, frederic@...nel.org
Subject: Re: lockdep splat in v5.11-rc1 involving console_sem and rq locks

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.

  https://lkml.kernel.org/r/20201226025117.2770-1-jiangshanlai@gmail.com