Commit ffe7c73a authored Aug 06, 2014 by Ville Syrjälä Committed by Daniel Vetter Aug 06, 2014

drm: Fix race between drm_vblank_off() and drm_queue_vblank_event()



Currently it's possible that the following will happen:
1. drm_wait_vblank() calls drm_vblank_get()
2. drm_vblank_off() gets called
3. drm_wait_vblank() calls drm_queue_vblank_event() which
   adds the event to the queue event though vblank interrupts
   are currently disabled (and may not be re-enabled ever again).

To fix the problem, add another vblank->enabled check into
drm_queue_vblank_event().

drm_vblank_off() holds event_lock around the vblank disable,
so no further locking needs to be added to drm_queue_vblank_event().
vblank disable from another source is not possible since
drm_wait_vblank() already holds a vblank reference.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

parent 56cc279b

drivers/gpu/drm/drm_irq.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -1270,6 +1270,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe,
		union drm_wait_vblank *vblwait,
		struct drm_file *file_priv)
		{
		struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
		struct drm_pending_vblank_event *e;
		struct timeval now;
		unsigned long flags;
		@@ -1293,6 +1294,18 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe,

		spin_lock_irqsave(&dev->event_lock, flags);

		/*
		* drm_vblank_off() might have been called after we called
		* drm_vblank_get(). drm_vblank_off() holds event_lock
		* around the vblank disable, so no need for further locking.
		* The reference from drm_vblank_get() protects against
		* vblank disable from another source.
		*/
		if (!vblank->enabled) {
		ret = -EINVAL;
		goto err_unlock;
		}

		if (file_priv->event_space < sizeof e->event) {
		ret = -EBUSY;
		goto err_unlock;