linux-kernel - Re: BUG: sleeping function called from invalid context on 3.10.10-rt7

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Date:	Wed, 11 Sep 2013 21:07:10 +0200
From:	Mario Kleiner <mario.kleiner@...bingen.mpg.de>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Peter Hurley <peter@...leysoftware.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Clark Williams <williams@...hat.com>,
	Dave Airlie <airlied@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Mario Kleiner <mario.kleiner@...bingen.mpg.de>
Subject: Re: BUG: sleeping function called from invalid context on 3.10.10-rt7

On 11.09.13 20:35, Steven Rostedt wrote:
> On Wed, 11 Sep 2013 20:29:07 +0200
> Mario Kleiner <mario.kleiner@...bingen.mpg.de> wrote:
>
>> That said, maybe preempt_disable is no longer the optimal choice there
>> and there's some better way to achieve good protection against
>> interruptions of that bit of code? My knowledge here is a bit rusty, and
>> the intel kms drivers and rt stuff has changed quite a bit.
>
> If you set your code to a higher priority than other tasks (and
> interrupts) than it wont be preempted there. Unless of course it blocks
> on a lock, but even then, priority inheritance will take place and it
> still should be rather quick. (unless the holder of the lock is doing
> that strange polling).
>
> -- Steve
>

Right, on a rt kernel. But that creates the problem of not very computer 
savvy users (psychologists and biologists mostly) somehow having to 
choose proper priorities for gpu interrupt threads and for the 
x-server/wayland/..., and not much protection on a non-rt kernel?

preempt_disable() a few years ago looked like a good "plug and play" 
default solution, because the ->get_crtc_scanoutpos() function was 
supposed to have a very low and bounded execution time. At the time we 
wrote the patches for intel/radeon/nouveau, that was the case. Typical 
execution time (= preempt off time) was like 1-4 usecs, even on very low 
end hardware.

Seems that at least intel's kms driver does a lot of things now, which 
can sleep and spin inside that section? I tried to follow the posted 
stack trace, but got lost somewhere around the i915_read32 code and 
power management stuff...

-mario
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