Re: Debugging Thinkpad T430s occasional suspend failure.

From: Hugh Dickins
Date: Thu Feb 14 2013 - 21:10:29 EST

On Thu, 14 Feb 2013, Dave Jones wrote:
> On Wed, Feb 13, 2013 at 11:56:25AM -0800, Linus Torvalds wrote:
> > On Wed, Feb 13, 2013 at 11:34 AM, Dave Jones <davej@xxxxxxxxxx> wrote:
> > >
> > > My test was a loop of 100 suspend/resume cycles before calling something
> > > 'good'. The 'bad' cases all failed within 10 cycles (usually 2-3).
> >
> > Considering that you apparently already found one case where the BIOS
> > crapped out due to effectively unrelated timing details (ie timing
> > triggered a temperature issue that then triggered behavioral changes),
> > I wonder if your more occasional problem might not be a sign of
> > something similar.
> >
> > But since you seem to be able to automate it well, maybe one thing to
> > try is to change the timing a bit while testing. Maybe some failures
> > were hidden by the timing just happening to work out.
> 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 <paul.mckenney@xxxxxxxxxx>
> 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. Perhaps when I reinstall, and switch to booting EFI
> I'll be able to use pstore, but on a bios-based boot, all hope seems lost.
> No netconsole, no usb-serial, even crippling i915's suspend routine doesn't help.
> I'll just disable this option for now.

Which won't affect my case since I never enabled it.

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