drm/i915: Insert cond_resched() into i915_gem_free_objects

As we may have very many objects to free, check to see if the task needs
to be rescheduled whilst freeing them.
Suggested-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170407102552.5781-4-chris@chris-wilson.co.ukReviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -4302,6 +4302,8 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
 	intel_runtime_pm_put(i915);
 	mutex_unlock(&i915->drm.struct_mutex);
 
+	cond_resched();
+
 	llist_for_each_entry_safe(obj, on, freed, freed) {
 		GEM_BUG_ON(obj->bind_count);
 		GEM_BUG_ON(atomic_read(&obj->frontbuffer_bits));