blk-cgroup: remove queue frozen from blkcg_activate_policy()

On the one hand, nest q_usage_counter under rq_qos_mutex is wrong;

On the other hand, policy activation is now all under queue frozen:
 - for bfq queue is frozen from elevator_change();
 - for blk-throttle, iocost, iolatency, queue is frozen from
 blkg_conf_open_bdev_frozen(&ctx);

Signed-off-by: Yu Kuai <[email protected]>
Reviewed-by: Nilay Shroff <[email protected]>

Author: hailan94

block/blk-cgroup.c

@@ -1580,12 +1580,13 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol)
 	struct request_queue *q = disk->queue;
 	struct blkg_policy_data *pd_prealloc = NULL;
 	struct blkcg_gq *blkg, *pinned_blkg = NULL;
-	unsigned int memflags;
 	int ret;
 
 	if (blkcg_policy_enabled(q, pol))
 		return 0;
 
+	WARN_ON_ONCE(q->mq_freeze_depth == 0);
+
 	/*
 	 * Policy is allowed to be registered without pd_alloc_fn/pd_free_fn,
 	 * for example, ioprio. Such policy will work on blkcg level, not disk
@@ -1594,8 +1595,6 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol)
 	if (WARN_ON_ONCE(!pol->pd_alloc_fn || !pol->pd_free_fn))
 		return -EINVAL;
 
-	if (queue_is_mq(q))
-		memflags = blk_mq_freeze_queue(q);
 retry:
 	spin_lock_irq(&q->queue_lock);
 
@@ -1658,8 +1657,6 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol)
 
 	spin_unlock_irq(&q->queue_lock);
 out:
-	if (queue_is_mq(q))
-		blk_mq_unfreeze_queue(q, memflags);
 	if (pinned_blkg)
 		blkg_put(pinned_blkg);
 	if (pd_prealloc)