linux-kernel - Re: [BISECTED] drm: random hang since 620f378 "drm: prune modes when ..."

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Date:	Sun, 13 Dec 2009 21:31:07 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	Dave Airlie <airlied@...hat.com>, Adam Jackson <ajax@...hat.com>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.sourceforge.net,
	keithp@...thp.com, eric@...olt.net, jbarnes@...tuousgeek.org,
	Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [BISECTED] drm: random hang since 620f378 "drm: prune modes when ..."

On Sunday 13 December 2009 20:00:18 Daniel Vetter wrote:
> On Sun, Dec 13, 2009 at 12:30:25PM +0000, Arnd Bergmann wrote:
> > And now it's obvious that my computer hates me. 12 hours of uptime, one reboot
> > to check the old other version is broken, it crashes. I reboot into the
> > good version, send out the above email and the next minute it crashes again.
> > c05422d52ee6b is not the culprit. Sorry Daniel for blaming your patch.
> 
> No problem. Looks like your hunting a pretty ugly Heisenbug. There's quite
> a interesting blog post by Paul McKenney, esp. the solution to "Quick Quiz 1"
> might be usefull in your case:
> 
> http://paulmck.livejournal.com/14639.html

Thanks! In fact I've actually read that post on the kernel planet and decided
to do basically a linear search through the i915 patches merged into 2.6.32.

The current result is 67cf781bea5 "drm/i915: Make the downclocking debug code
be under DRM_DEBUG not DRM_ERROR." is known bad, while 043029655 "drm/i915:
Support IGD EOS" is probably good, pointing to Jesses 652c393a33 "drm/i915:
add dynamic clock frequency control" as the next best guess. Unfortunately,
that is a rather large change that is not easy to revert on current kernels.

I'll keep running my machine on the 043029655 level and tell you if it keeps
working a few more days.

	Arnd
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