Re: [regression bisected] HR-timers bug >=2.6.25

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, 15 May 2008, Justin Madru wrote:
> I've reported this problem previously:
> http://lkml.org/lkml/2008/3/12/290
> http://bugzilla.kernel.org/show_bug.cgi?id=10235
> https://bugs.freedesktop.org/show_bug.cgi?id=15602
> 
> This bug is still in mainline as of 2.6.26-rc1. (affected versions 2.6.25-rc0
> - 2.6.26-rc1)
> 
> Ever since 2.6.25-rc3 (the first rc I tested), my screen would blank out when
> mode switching from the Ubuntu uplash to the gdm login. Normally after the
> boot splash, the screen goes black and "refreshes" to select the correct
> resolution. But when using a kernel newer than 2.6.24 the screen doesn't come
> back on - it stays blank. This doesn't happen every time, but a good majority
> of the time. The workaround is to disable the splash, and that fixes the
> problem almost completely.
> 
> I did a git bisect. Rebooting 3 times if the problem didn't occur just to make
> sure.
> The git bisect reports that it's timing related - which is what Jesse Barnes
> said it could be.

Well, it's a timing problem related to splash which is exposed by the
scheduler timing changes. This is neither a hrtimer nor a scheduler
bug. Something in the splash / video driver switchover relies on some
obscure timing which is nowhere guaranteed.

Thanks,
	tglx