linux-kernel - Re: [Intel-gfx] BUG: sleeping function called from invalid context on 3.10.10-rt7

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Date:	Wed, 25 Sep 2013 10:13:01 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mario Kleiner <mario.kleiner@...bingen.mpg.de>
Cc:	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Peter Hurley <peter@...leysoftware.com>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Clark Williams <williams@...hat.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Dave Airlie <airlied@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>
Subject: Re: [Intel-gfx] BUG: sleeping function called from invalid context
 on 3.10.10-rt7

On Wed, 25 Sep 2013 06:32:10 +0200
Mario Kleiner <mario.kleiner@...bingen.mpg.de> wrote:

 
> But given the new situation, your proposal is great! If we push the 
> clock readouts into the get_scanoutpos routine, we can make this robust 
> without causing grief for the rt people and without the need for a new 
> separate lock for display regs in intel-kms.
> 
> E.g., for intel-kms:
> 
> i915_get_crtc_scanoutpos(..., ktime_t *stime, ktime_t *etime)
> {
>    ...
>    spin_lock_irqsave(...uncore.lock);
>    preempt_disable();
>    *stime = ktime_get();
>    position = __raw_i915_read32(dev_priv, PIPEDSL(pipe));
>    *etime = ktime_get();
>    preempt_enable();
>    spin_unlock_irqrestore(...uncore.lock)
>    ...
> }
> 
> With your patchset to reduce the amount of register reads needed in that 
> function, and given that forcewake handling isn't needed for these 
> registers, this should make it robust again and wouldn't need new locks.
> 
> Unless ktime_get is also a bad thing to do in a preempt disabled section?

ktime_get() works fine in preempt_disable sections, although it may add
some latencies, but you shouldn't need to worry about it.

I like this solution the best too, but if it does go in, I would ask to
send us the patch for adding the preempt_disable() and we can add the
preempt_disable_rt() to it. Why make mainline have a little more
overhead?

-- Steve
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