linux-kernel - Re: [PATCH] nohz: Fix spurious warning when hrtimer and clockevent get out of sync

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Date:   Fri, 9 Jun 2017 14:26:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
Cc:     Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...hat.com>,
        James Hartsock <hartsjc@...hat.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Tim Wright <tim@...bash.co.uk>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH] nohz: Fix spurious warning when hrtimer and clockevent
 get out of sync

On Fri, Jun 09, 2017 at 12:13:49PM +0000, Levin, Alexander (Sasha Levin) wrote:
> On Fri, Jun 09, 2017 at 02:48:57AM +0200, Frederic Weisbecker wrote:
> > On Thu, Jun 08, 2017 at 10:13:38PM +0000, Levin, Alexander (Sasha Levin) wrote:
> > > On Thu, Jun 08, 2017 at 09:07:05PM +0200, Frederic Weisbecker wrote:
> > > > Awesome, these traces have been very helpful! So now I think I get what's going on.
> > > > Can you please test the following fix?
> > > 
> > > With the patch, I hit the warning early on boot:
> > > 
> > > [    1.423727] clocksource: Switched to clocksource kvm-clock
> > > [    1.429326] ------------[ cut here ]------------
> > > [    1.430234] WARNING: CPU: 1 PID: 0 at kernel/time/tick-sched.c:792 __tick_nohz_idle_enter+0xe1c/0x15c0
> > 
> > Oh sorry, I inverted some conditional. It warns as soon as the tick is completely stopped
> > and not just deferred, which seldom happen on my testbox.
> > 
> > I need to learn programming again.
> > 
> > Here is the fixed version:
> 
> These warnings seem to have gone away, but I've started seeing a new one:
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 12525 at kernel/time/hrtimer.c:805 hrtimer_forward+0x222/0x3e0 kernel/time/hrtimer.c:805
> Kernel panic - not syncing: panic_on_warn set ...

https://lkml.kernel.org/r/20170609104457.GA39907@inn.lkp.intel.com

has a very similar splat