linux-kernel - Re: sched/core warning triggers on rcu torture test

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Date:   Tue, 26 Jun 2018 18:32:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: sched/core warning triggers on rcu torture test

On Tue, Jun 26, 2018 at 06:16:04PM +0200, Anna-Maria Gleixner wrote:
> Hi,
> 
> during rcu torture tests (TREE04 and TREE07) I noticed, that a
> WARN_ON_ONCE() in sched core triggers on a recent 4.18-rc2 based
> kernel (6f0d349d922b ("Merge
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net")) as well as
> on a 4.17.3.
> 
> I'm running the tests on a machine with 144 cores:
> 
>   tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 144 --duration 120 --configs "9*TREE07"
>   tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 144 --duration 120 --configs "18*TREE04"
> 
> 
> The warning was introduced by commit d84b31313ef8 ("sched/isolation:
> Offload residual 1Hz scheduler tick").
> 
> 
> Output looks similar for all tests I did (this one is the output of
> the 4.18-rc2 based kernel):
> 
> WARNING: CPU: 11 PID: 906 at kernel/sched/core.c:3138 sched_tick_remote+0xb6/0xc0

That's nohz_full stuff, is that a normal part of rcutorture? In any
case, is the one housekeeping CPU getting seriously overloaded or
something?