It would race between userspace thread and commit worker. Ie. vblank irq would trigger event and userspace could begin the next atomic update, before the commit worker had a chance to clear the pending flag. If we do end up needing something to prevent userspace from trying another pageflip before getting vblank event, it should probably be implemented as a pending_planes bitmask, similar to pending_crtcs. See start_atomic() and end_atomic(). Signed-off-by: Rob Clark <robdclark@gmail.com>