linux-kernel - Re: PPro arch_cpu_idle: NMI watchdog: Watchdog detected hard LOCKUP on cpu 1

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Date:   Mon, 6 Mar 2017 00:19:54 +0100
From:   Frederic Weisbecker <fweisbec@...il.com>
To:     Meelis Roos <mroos@...ux.ee>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel list <linux-kernel@...r.kernel.org>,
        x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: PPro arch_cpu_idle: NMI watchdog: Watchdog detected hard LOCKUP
 on cpu 1

On Sun, Mar 05, 2017 at 10:48:50PM +0200, Meelis Roos wrote:
> Added some CC-s because of bisect find. Whole context should be still 
> here.
> 
> > > > > > > This is on my trusty IBM PC365, dual Pentium Pro. 4.10 worked fine, 
> > > > > > > 4.10.0-09686-g9e314890292c and 4.10.0-10770-g2d6be4abf514 exhibit a 
> > > > > > > problem. Ocassionally NMI watchdog kicks in and discovers one of the 
> > > > > > > CPUs in LOCKUP. The system keeps running fine. The first lockup was 
> > > > > > > different, all the others were from arch_cpu_idle. Sometime ecey couple 
> > > > > > > of seconds (after some activity), sometimes nothing for a long time 
> > > > > > > (idle, no SSH logins).
> > > > > > 
> > > > > > The only watchdog related patch which hit after 4.10 is:
> > > > > > 
> > > > > >  8dcde9def5a1 kernel/watchdog.c: do not hardcode CPU 0 as the initial thread
> > > > > > 
> > > > > > Can you try to revert that for a start? I'm not seeing why it should be the
> > > > > > culprit from a quick glance, but ...
> > > > > 
> > > > > Reverting this patch does not help.
> > > > 
> > > > I did not expect that, but excluding it was a valid shot in the
> > > > dark. Thanmks for trying.
> > > > 
> > > > To be honest, I have no idea what causes that at the moment, but I will
> > > > come back to you tomorrow after thinking it through (with brain awake) how
> > > > to debug this.
> > > 
> > > Went through the related changes which came in during the merge window. One
> > > which affects the per cpu timers is: 914122c389d0
> > > 
> > > Can you try to revert that one please?
> > 
> > Running out of obvious culprits. Any chance that you can do a bisect or
> > this too painful on that box?
> 
> Done on a P4 where the problem also appeared. The bisecting resulted in 
> this commit. Does it seem realistic? I will also try if this help son 
> the old PPro.
> 
> 93825f2ec736f30e034ab7c9d56b42849c5b00da is the first bad commit
> commit 93825f2ec736f30e034ab7c9d56b42849c5b00da
> Author: Frederic Weisbecker <fweisbec@...il.com>
> Date:   Tue Jan 31 04:09:16 2017 +0100
> 
>     jiffies: Reuse TICK_NSEC instead of NSEC_PER_JIFFY
>     
>     NSEC_PER_JIFFY is an ad-hoc redefinition of TICK_NSEC. Let's rather
>     use a unique and well maintained version.
>     
>     Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
>     Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>     Cc: Paul Mackerras <paulus@...ba.org>
>     Cc: Michael Ellerman <mpe@...erman.id.au>
>     Cc: Heiko Carstens <heiko.carstens@...ibm.com>
>     Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
>     Cc: Tony Luck <tony.luck@...el.com>
>     Cc: Fenghua Yu <fenghua.yu@...el.com>
>     Cc: Peter Zijlstra <peterz@...radead.org>
>     Cc: Rik van Riel <riel@...hat.com>
>     Cc: Stanislaw Gruszka <sgruszka@...hat.com>
>     Cc: Wanpeng Li <wanpeng.li@...mail.com>
>     Link: http://lkml.kernel.org/r/1485832191-26889-1-git-send-email-fweisbec@gmail.com
>     Signed-off-by: Ingo Molnar <mingo@...nel.org>

Ouch, looking at that patch again, I probably had a delusional moment when I wrote this:

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index a4a0e47..7906b3f 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -125,7 +125,7 @@ int register_refined_jiffies(long cycles_per_second)
 	shift_hz += cycles_per_tick/2;
 	do_div(shift_hz, cycles_per_tick);
 	/* Calculate nsec_per_tick using shift_hz */
-	nsec_per_tick = (u64)NSEC_PER_SEC << 8;
+	nsec_per_tick = (u64)TICK_NSEC << 8;
 	nsec_per_tick += (u32)shift_hz/2;
 	do_div(nsec_per_tick, (u32)shift_hz);
 


Could you please retry after reverting this specific chunk? (that would be the very fix
to apply).

Thanks!