Both as an exercise to document that we are reading the state outside of
the appropriate mutex and to ensure that we only read the value once
before the multiple comparisons, use READ_ONCE.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170513105201.17658-1-chris@chris-wilson.co.uk