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SubjectRe: Debugging Thinkpad T430s occasional suspend failure.
On Thu, Feb 14, 2013 at 06:09:44PM -0800, Linus Torvalds wrote:
> On Thu, Feb 14, 2013 at 5:15 PM, Dave Jones <> wrote:
> >
> > Given I never saw this on a Fedora kernel, just my self-built ones, I eventually
> > gave up on bisecting code, and switched to bisecting config options.
> > I should have started this way, as I figured it out within an hour.
> >
> > 3.7 merge window is when I started seeing this, and here's what got introduced
> > during that time..
> >
> > commit e3ebfb96f396731ca2d0b108785d5da31b53ab00
> > Author: Paul E. McKenney <>
> > Date: Mon Jul 2 14:42:01 2012 -0700
> >
> > rcu: Add PROVE_RCU_DELAY to provoke difficult races
> >
> > 'difficult' is an understatement. This explains why some of those 'good'
> > bisects survived 100 suspends on one day, and failed the next.
> >
> > Unfortunatly, I don't think there's any sane way to retrieve whatever debug
> > info might be getting spewed.
> Hmm. I have to say, that's a particularly unhelpful config option. It
> may make races much easier to hit, but when you do hit them, what's
> the symptoms of said race?
> Paul? Apparently you end up with a dead machine at least during resume
> and no oops. Which isn't very helpful. Maybe there is possibly some
> BUG_ON() in the RCU code somewhere?
> So Paul, if you know what the common symptoms of the bug that that
> debug option helps trigger are, is there some way to make them less
> lethal and still print out useful information?

This commit was designed to increase the probability of hitting the
races described in These races result
in deadlocks involving the runqueue lock (and perhaps also the priority
inheritance locks). And yes, I most certainly should have described
this in the commit message. :-(

So it looks like Dave is hitting some other race/bug than the one that
this commit was designed to expose.

I must confess that I don't know how to proceed without any meaningful
debug information here. Feel free to revert the above commit if you would
like -- I can of course always maintain it locally for my own testing.

Thanx, Paul

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