linux-kernel - Re: [patch 1/4] Ignore stolen time in the softlockup watchdog

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Message-Id: <20070424133359.f18bce78.akpm@linux-foundation.org>
Date:	Tue, 24 Apr 2007 13:33:59 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Prarit Bhargava <prarit@...hat.com>,
	Rick Lindsley <ricklind@...ibm.com>,
	john stultz <johnstul@...ibm.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	virtualization@...ts.osdl.org,
	Chris Lalancette <clalance@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 1/4] Ignore stolen time in the softlockup watchdog

On Tue, 24 Apr 2007 13:24:24 -0700 Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Jeremy Fitzhardinge wrote:
> > Andrew Morton wrote:
> >   
> >> Well, it _is_ mysterious.
> >>
> >> Did you try to locate the code which failed?  I got lost in macros and
> >> include files, and gave up very very easily.  Stop hiding, Ingo.
> >>   
> >>     
> >
> > OK, I've managed to reproduce it.  Removing the local_irq_save/restore
> > from sched_clock() makes it go away, as I'd expect (otherwise it would
> > really be magic).  But given that it never seems to touch the softlockup
> > during testing, I have no idea what difference it makes...
> 
> And sched_clock's use of local_irq_save/restore appears to be absolutely
> correct, so I think it must be triggering a bug in either the self-tests
> or lockdep itself.

It's weird.  And I don't think the locking selftest code calls
sched_clock() (or any other time-related thing) at all, does it?

> The only way I could actually extract the test code itself was to run
> the whole thing through cpp+indent, but it doesn't shed much light.
> 
> It's also not clear to me if there are 6 independent failures, or if
> they're a cascade.

Oh well.  I'll restore the patches and when people hit problems we can
blame Ingo!

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