linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Wed, 3 Dec 2014 18:21:15 -0500
From:	Dave Jones <davej@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: frequent lockups in 3.18rc4

On Wed, Dec 03, 2014 at 11:19:11PM +0100, Thomas Gleixner wrote:
 > On Wed, 3 Dec 2014, Linus Torvalds wrote:
 > > On Wed, Dec 3, 2014 at 12:55 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
 > > >
 > > > But it's always negative, which means HPET is always ahead of
 > > > TSC. That excludes pretty much the clocksource watchdog starvation
 > > > issue which results in TSC being ahead of HPET due to a HPET
 > > > wraparound (which takes ~300s).
 > > 
 > > Still, I'd be more likely to trust the TSC than the HPET on modern
 > > machines.. And DaveJ's machine isn't some old one.
 > 
 > Well, that does not explain the softlock watchdog which is solely
 > relying on the TSC.
 > 
 > > Of course, there's always BIOS games. Can we read the TSC offset
 > > register and check it being constant (modulo sleep events)?
 > 
 > The kernel does not touch it. Here is a untested hack to verify it on
 > every local apic timer interrupt. Not nice, but simple :)
 
 > +			pr_err("TSC adjustment on cpu %d changed %llu -> %llu\n",
 > +			       cpu,
 > +			       (unsigned long long) __this_cpu_read(tsc_adjust),
 > +			       (unsigned long long) adj);

I just got 

[ 1472.614433] Clocksource tsc unstable (delta = -26373048906 ns)

without any sign of the pr_err above.

	Dave
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