[Intel-gfx] [PATCH] drm/i915: Don't clobber crtc->fb when queue_flip fails

[Ville Syrjälä]

On Fri, Feb 22, 2013 at 01:31:35PM +0000, Chris Wilson wrote:
> On Fri, Feb 22, 2013 at 02:17:24PM +0200, ville.syrjala at linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > Point crtc->fb the the new framebuffer only after we know that the flip
> > was succesfully queued.
> > 
> > While at it, move the intel_fb and obj assignments a bit close to where
> > they're used.
> > 
> > Cc: stable at vger.kernel.org
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Hmm, that exposes us to a FlipDone interrupt seeing the old crtc->fb.
> That looks safe enough, but can you see how ugly restoring the old_fb
> looks in comparison?

I don't think anyone should be poking at crtc->fb w/o holding the crtc
mutex. Except that intel_update_fbc() actually does. That thing would
appear to be just broken since it crawls around in the crtc state w/o
proper protection. The fb could even disappear from under it.

But if you prefer the set/restore approach I'll send out a version
doing that.

-- 
Ville Syrjälä
Intel OTC