drm/i915: Mark up vma->active as safe for use inside shrinkers

Since a shrinker may be forced to wait on GPU activity,
i915_active_wait(&vma->active) must be safe for use inside a shrinker,
and so let's mark up the lock as being acquired by the shrinker to avoid
any nasty surprises creeping in.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190703091726.11690-8-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_vma.c

@@ -22,6 +22,7 @@
  *
  */
 
+#include <linux/sched/mm.h>
 #include <drm/drm_gem.h>
 
 #include "display/intel_frontbuffer.h"
@@ -120,6 +121,13 @@ vma_create(struct drm_i915_gem_object *obj,
 			 __i915_vma_active, __i915_vma_retire);
 	INIT_ACTIVE_REQUEST(&vma->last_fence);
 
+	/* Declare ourselves safe for use inside shrinkers */
+	if (IS_ENABLED(CONFIG_LOCKDEP)) {
+		fs_reclaim_acquire(GFP_KERNEL);
+		might_lock(&vma->active.mutex);
+		fs_reclaim_release(GFP_KERNEL);
+	}
+
 	INIT_LIST_HEAD(&vma->closed_link);
 
 	if (view && view->type != I915_GGTT_VIEW_NORMAL) {