drm/shmobile: Fix race condition between page flip request and handler
authorLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tue, 12 Mar 2013 14:38:43 +0000 (15:38 +0100)
committerDave Airlie <airlied@redhat.com>
Fri, 26 Apr 2013 00:21:57 +0000 (10:21 +1000)
commit17f0efc4f463e5b74026863521cbd47fb93f5686
tree9f8b91f9950085758565c499b8eec33ec21958c0
parentd50289958076f7b2dd0f775341807da1e953f587
drm/shmobile: Fix race condition between page flip request and handler

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>
Signed-off-by: Dave Airlie <airlied@redhat.com>
drivers/gpu/drm/shmobile/shmob_drm_crtc.c