Re: Debugging Thinkpad T430s occasional suspend failure.

From: Dave Jones
Date: Thu Feb 14 2013 - 20:15:17 EST

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.


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