bfq: Track whether bfq_group is still online

Track whether bfq_group is still online. We cannot rely on
blkcg_gq->online because that gets cleared only after all policies are
offlined and we need something that gets updated already under
bfqd->lock when we are cleaning up our bfq_group to be able to guarantee
that when we see online bfq_group, it will stay online while we are
holding bfqd->lock lock.

CC: stable@vger.kernel.org
Tested-by: "yukuai (C)" <yukuai3@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220401102752.8599-7-jack@suse.czSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-cgroup.c

@@ -557,6 +557,7 @@ static void bfq_pd_init(struct blkg_policy_data *pd)
 				   */
 	bfqg->bfqd = bfqd;
 	bfqg->active_entities = 0;
+	bfqg->online = true;
 	bfqg->rq_pos_tree = RB_ROOT;
 }
 
@@ -603,7 +604,6 @@ struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd,
 	struct bfq_entity *entity;
 
 	bfqg = bfq_lookup_bfqg(bfqd, blkcg);
-
 	if (unlikely(!bfqg))
 		return NULL;
 
@@ -979,6 +979,7 @@ static void bfq_pd_offline(struct blkg_policy_data *pd)
 
 put_async_queues:
 	bfq_put_async_queues(bfqd, bfqg);
+	bfqg->online = false;
 
 	spin_unlock_irqrestore(&bfqd->lock, flags);
 	/*

block/bfq-iosched.h

@@ -928,6 +928,8 @@ struct bfq_group {
 
 	/* reference counter (see comments in bfq_bic_update_cgroup) */
 	int ref;
+	/* Is bfq_group still online? */
+	bool online;
 
 	struct bfq_entity entity;
 	struct bfq_sched_data sched_data;