[PATCH] drm/shmobile: Fix race condition between page flip request and handler

[Laurent Pinchart]

On Thursday 28 March 2013 16:10:02 Laurent Pinchart wrote:
> Hi Dave,
> 
> Could you please pick this patch for v3.10 ?

Ping ?

> On Tuesday 12 March 2013 15:38:43 Laurent Pinchart wrote:
> > The page flip handler stores the page flip event pointer and then calls
> > drm_vblank_get() to enable the vblank interrupt. Due to the vblank off
> > delay, the vblank interrupt can be enabled in the hardware at that
> > point, even if the vblank reference count is equal to 0. If a vblank
> > interrupt is triggered between storing the event pointer and calling
> > drm_vblank_get(), the page flip completion handler will process the
> > event and call drm_vblank_put() with a reference count equal to 0. This
> > will result in a BUG_ON.
> > 
> > Fix the race condition by calling drm_vblank_get() before storing the
> > event pointer.
> > 
> > Signed-off-by: Laurent Pinchart
> > <laurent.pinchart+renesas at ideasonboard.com>
> > ---
> > 
> >  drivers/gpu/drm/shmobile/shmob_drm_crtc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/shmobile/shmob_drm_crtc.c
> > b/drivers/gpu/drm/shmobile/shmob_drm_crtc.c index d917a41..7dff49e 100644
> > --- a/drivers/gpu/drm/shmobile/shmob_drm_crtc.c
> > +++ b/drivers/gpu/drm/shmobile/shmob_drm_crtc.c
> > @@ -494,10 +494,10 @@ static int shmob_drm_crtc_page_flip(struct drm_crtc
> > *crtc,
> > 
> >  	if (event) {
> >  	
> >  		event->pipe = 0;
> > 
> > +		drm_vblank_get(dev, 0);
> > 
> >  		spin_lock_irqsave(&dev->event_lock, flags);
> >  		scrtc->event = event;
> >  		spin_unlock_irqrestore(&dev->event_lock, flags);
> > 
> > -		drm_vblank_get(dev, 0);
> > 
> >  	}
> >  	
> >  	return 0;
-- 
Regards,

Laurent Pinchart