drm/i915: Drain freed objects for mmap space exhaustion

As we now use a deferred free queue for objects, simply retiring the
active objects is not enough to immediately free them and recover their
mmap space - we must now also drain the freed object list.

Fixes: fbbd37b36fa5 ("drm/i915: Move object release to a freelist + worker"
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: <drm-intel-fixes@lists.freedesktop.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170106152240.5793-3-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -2090,23 +2090,21 @@ static int i915_gem_object_create_mmap_offset(struct drm_i915_gem_object *obj)
 	int err;
 
 	err = drm_gem_create_mmap_offset(&obj->base);
-	if (!err)
+	if (likely(!err))
 		return 0;
 
-	/* We can idle the GPU locklessly to flush stale objects, but in order
-	 * to claim that space for ourselves, we need to take the big
-	 * struct_mutex to free the requests+objects and allocate our slot.
-	 */
-	err = i915_gem_wait_for_idle(dev_priv, I915_WAIT_INTERRUPTIBLE);
-	if (err)
-		return err;
+	/* Attempt to reap some mmap space from dead objects */
+	do {
+		err = i915_gem_wait_for_idle(dev_priv, I915_WAIT_INTERRUPTIBLE);
+		if (err)
+			break;
 
-	err = i915_mutex_lock_interruptible(&dev_priv->drm);
-	if (!err) {
-		i915_gem_retire_requests(dev_priv);
+		i915_gem_drain_freed_objects(dev_priv);
 		err = drm_gem_create_mmap_offset(&obj->base);
-		mutex_unlock(&dev_priv->drm.struct_mutex);
-	}
+		if (!err)
+			break;
+
+	} while (flush_delayed_work(&dev_priv->gt.retire_work));
 
 	return err;
 }