linux-kernel - Re: [PATCH] sched/debug: Reset watchdog on all CPUs while processing sysrq-t

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Message-ID: <20200107093214.GV2844@hirez.programming.kicks-ass.net>
Date:   Tue, 7 Jan 2020 10:32:14 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Wei Li <liwei391@...wei.com>, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
        huawei.libin@...wei.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/debug: Reset watchdog on all CPUs while processing
 sysrq-t

On Thu, Jan 02, 2020 at 02:45:14PM -0500, Steven Rostedt wrote:
> On Thu, 26 Dec 2019 16:52:24 +0800
> Wei Li <liwei391@...wei.com> wrote:
> 
> > Lengthy output of sysrq-t may take a lot of time on slow serial console
> > with lots of processes and CPUs.
> > 
> > So we need to reset NMI-watchdog to avoid spurious lockup messages, and
> > we also reset softlockup watchdogs on all other CPUs since another CPU
> > might be blocked waiting for us to process an IPI or stop_machine.
> 
> Have you had this triggered?
> 
> > 
> > Add to sysrq_sched_debug_show() as what we did in show_state_filter().
> > 
> > Signed-off-by: Wei Li <liwei391@...wei.com>
> > ---
> >  kernel/sched/debug.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> > index f7e4579e746c..879d3ccf3806 100644
> > --- a/kernel/sched/debug.c
> > +++ b/kernel/sched/debug.c
> > @@ -751,9 +751,16 @@ void sysrq_sched_debug_show(void)
> >  	int cpu;
> >  
> >  	sched_debug_header(NULL);
> > -	for_each_online_cpu(cpu)
> > +	for_each_online_cpu(cpu) {
> > +		/*
> > +		 * Need to reset softlockup watchdogs on all CPUs, because
> > +		 * another CPU might be blocked waiting for us to process
> > +		 * an IPI or stop_machine.
> > +		 */
> > +		touch_nmi_watchdog();
> > +		touch_all_softlockup_watchdogs();
> 
> This doesn't seem to hurt to add, thus.
> 
> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Thanks!