drm-vblank: Always return true vblank count of scheduled vblank event.

This patch tries to make sure that the vbl.reply.sequence
vblank count for a queued or emitted vblank event always
corresponds to the true vblank count of queueing/emission, so
the ddx can rely on the returned target_msc for consistency
checks and implementation of swap_intervals in glXSwapBuffers().

Without this there is a small race-condition between the
userspace ddx queueing a vblank event and the vblank
counter incrementing before the event gets queued in
the kernel.

Signed-off-by: Mario Kleiner <mario.kleiner@tuebingen.mpg.de>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 4e82d0d3c378..55160d7c38b6 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1086,15 +1086,18 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe,
 
         e->event.sequence = vblwait->request.sequence;
         if ((seq - vblwait->request.sequence) <= (1 << 23)) {
+                e->event.sequence = seq;
                 e->event.tv_sec = now.tv_sec;
                 e->event.tv_usec = now.tv_usec;
                 drm_vblank_put(dev, e->pipe);
                 list_add_tail(&e->base.link, &e->base.file_priv->event_list);
                 wake_up_interruptible(&e->base.file_priv->event_wait);
+                vblwait->reply.sequence = seq;
                 trace_drm_vblank_event_delivered(current->pid, pipe,
                                                  vblwait->request.sequence);
         } else {
                 list_add_tail(&e->base.link, &dev->vblank_event_list);
+                vblwait->reply.sequence = vblwait->request.sequence;
         }
 
         spin_unlock_irqrestore(&dev->event_lock, flags);