drm: Use vblank_disable_and_save in drm_vblank_cleanup()

Calling vblank_disable_fn() will cause that function to no-op
if !dev->vblank_disable_allowed for some kms drivers, e.g.,
on nouveau-kms. This can cause the gpu vblank irq's to not get
disabled before freeing the dev->vblank array, so if a
vblank irq fires and calls into drm_handle_vblank() after
drm_vblank_cleanup() completes, it will cause use-after-free
access to dev->vblank array.

Call vblank_disable_and_save unconditionally, so vblank irqs
are guaranteed to be off, before we delete the data structures
on which they operate.

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[danvet: Fix subsystem name in patch subject.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_irq.c

@@ -239,6 +239,7 @@ static void vblank_disable_fn(unsigned long arg)
 void drm_vblank_cleanup(struct drm_device *dev)
 {
 	int crtc;
+	unsigned long irqflags;
 
 	/* Bail if the driver didn't call drm_vblank_init() */
 	if (dev->num_crtcs == 0)
@@ -248,7 +249,10 @@ void drm_vblank_cleanup(struct drm_device *dev)
 		struct drm_vblank_crtc *vblank = &dev->vblank[crtc];
 
 		del_timer_sync(&vblank->disable_timer);
-		vblank_disable_fn((unsigned long)vblank);
+
+		spin_lock_irqsave(&dev->vbl_lock, irqflags);
+		vblank_disable_and_save(dev, crtc);
+		spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
 	}
 
 	kfree(dev->vblank);