On Wed, Aug 06, 2014 at 02:49:52PM +0300, ville.syrjala@xxxxxxxxxxxxxxx wrote:
> 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>
I guess the window is too small here to make this reproducible in a test?
Especially since each attempt will take a few hundred ms ...
-Daniel
> ---
> 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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--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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