linux-kernel - Re: Alleged fix for writer stall on -rcu branch dev

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Message-Id: <20190415105645.GQ14111@linux.ibm.com>
Date:   Mon, 15 Apr 2019 03:56:45 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: Alleged fix for writer stall on -rcu branch dev

On Mon, Apr 15, 2019 at 12:40:47PM +0200, Sebastian Andrzej Siewior wrote:
> On 2019-04-13 07:21:53 [-0700], Paul E. McKenney wrote:
> > 
> > And after ramping up the stress in rcutorture a bit, I am able to
> > reproduce this CPU stall involving offlining on my systems.  My plan is
> > my usual one:  Keep increasing rcutorture stress to get it to reproduce
> > in reasonable time, add diagnostics as appropriate, and continue making
> > forward-progress improvements in RCU itself.
> 
> I *think* this one is also new:
> 
> |Assertion failure in /home/bigeasy/linux-rt/tools/testing/selftests/rcutorture/res/2019.04.14-14:28:40/TREE03.37/console.log TREE03
> |Summary: Warnings: 6 Call Traces: 6
> https://breakpoint.cc/console-03.37.log

This is new in rcutorture as well.  It is complaining that we just got
done with a stutter interval (in which torturing temporarily stops)
but not everything has progressed through the callback chain to be freed.
And in this case it is happening during rcutorture shutdown, so I need
to check the callback -- I might need end-of-run checks in that WARN_ON().

> |Assertion failure in /home/bigeasy/linux-rt/tools/testing/selftests/rcutorture/res/2019.04.14-14:28:40/TREE03.39/console.log TREE03
> |Summary: Warnings: 4 Call Traces: 4
> https://breakpoint.cc/console-03.39.log

And the same here.  So neither count against you.  ;-)

							Thanx, Paul

> This is still commit 33e04e451279 ("torture: Allow inter-stutter interval to be
> specified").
> 
> > Thank you very much for locating this one!!!
> 
> You are welcome.
> 
> > 							Thanx, Paul
> 
> Sebastian
>