Re: [PATCH] drm/shmobile: Fix race condition between page flip request and handler

Hi Dave,

Could you please pick this patch for v3.10 ?

On Tuesday 12 March 2013 15:38:43 Laurent Pinchart wrote:

The page flip handler stores the page flip event pointer and then calls drm_vblank_get() to enable the vblank interrupt. Due to the vblank off delay, the vblank interrupt can be enabled in the hardware at that point, even if the vblank reference count is equal to 0. If a vblank interrupt is triggered between storing the event pointer and calling drm_vblank_get(), the page flip completion handler will process the event and call drm_vblank_put() with a reference count equal to 0. This will result in a BUG_ON.

Fix the race condition by calling drm_vblank_get() before storing the event pointer.

Signed-off-by: Laurent Pinchart laurent.pinchart+renesas@ideasonboard.com

drivers/gpu/drm/shmobile/shmob_drm_crtc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/shmobile/shmob_drm_crtc.c b/drivers/gpu/drm/shmobile/shmob_drm_crtc.c index d917a41..7dff49e 100644 --- a/drivers/gpu/drm/shmobile/shmob_drm_crtc.c +++ b/drivers/gpu/drm/shmobile/shmob_drm_crtc.c @@ -494,10 +494,10 @@ static int shmob_drm_crtc_page_flip(struct drm_crtc *crtc,

if (event) { event->pipe = 0;

• drm_vblank_get(dev, 0);
  

  spin_lock_irqsave(&dev->event_lock, flags); scrtc->event = event; spin_unlock_irqrestore(&dev->event_lock, flags);

• drm_vblank_get(dev, 0);
  

  }

  return 0;