drm/i915: Assert that fence->lock is held in an irq-safe manner

Everytime we take the fence->lock (aka request->lock), we must do so
with irqs disabled since it may be used from within an hardirq context.
As sometimes we are taking the lock in a nested manner, assert that the
caller did disable the irqs for us.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170302115130.28434-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_breadcrumbs.c

@@ -653,6 +653,7 @@ void intel_engine_enable_signaling(struct drm_i915_gem_request *request)
 	 */
 
 	/* locked by dma_fence_enable_sw_signaling() (irqsafe fence->lock) */
+	GEM_BUG_ON(!irqs_disabled());
 	assert_spin_locked(&request->lock);
 
 	seqno = i915_gem_request_global_seqno(request);
@@ -709,6 +710,7 @@ void intel_engine_cancel_signaling(struct drm_i915_gem_request *request)
 	struct intel_engine_cs *engine = request->engine;
 	struct intel_breadcrumbs *b = &engine->breadcrumbs;
 
+	GEM_BUG_ON(!irqs_disabled());
 	assert_spin_locked(&request->lock);
 	GEM_BUG_ON(!request->signaling.wait.seqno);