block: wake up waiters when a queue is marked dying

If it's dying, we can't expect new request to complete and come
in an wake up other tasks waiting for requests. So after we
have marked it as dying, wake up everybody currently waiting
for a request. Once they wake, they will retry their allocation
and fail appropriately due to the state of the queue.

Tested-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 32e8dbb..60c9d4a 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -68,9 +68,9 @@
 }
 
 /*
- * Wakeup all potentially sleeping on normal (non-reserved) tags
+ * Wakeup all potentially sleeping on tags
  */
-static void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags)
+void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)
 {
 	struct blk_mq_bitmap_tags *bt;
 	int i, wake_index;
@@ -85,6 +85,12 @@
 
 		wake_index = bt_index_inc(wake_index);
 	}
+
+	if (include_reserve) {
+		bt = &tags->breserved_tags;
+		if (waitqueue_active(&bt->bs[0].wait))
+			wake_up(&bt->bs[0].wait);
+	}
 }
 
 /*
@@ -100,7 +106,7 @@
 
 	atomic_dec(&tags->active_queues);
 
-	blk_mq_tag_wakeup_all(tags);
+	blk_mq_tag_wakeup_all(tags, false);
 }
 
 /*
@@ -584,7 +590,7 @@
 	 * static and should never need resizing.
 	 */
 	bt_update_count(&tags->bitmap_tags, tdepth);
-	blk_mq_tag_wakeup_all(tags);
+	blk_mq_tag_wakeup_all(tags, false);
 	return 0;
 }