From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
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@xxxxxxxxx>
Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_irq.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 9353609..b2428cb 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -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;
--
1.8.5.5
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