block: don't allow the same type rq_qos add more than once

In our test of iocost, we encountered some list add/del corruptions of
inner_walk list in ioc_timer_fn.

The reason can be described as follows:

cpu 0					cpu 1
ioc_qos_write				ioc_qos_write

ioc = q_to_ioc(queue);
if (!ioc) {
        ioc = kzalloc();
					ioc = q_to_ioc(queue);
					if (!ioc) {
						ioc = kzalloc();
						...
						rq_qos_add(q, rqos);
					}
        ...
        rq_qos_add(q, rqos);
        ...
}

When the io.cost.qos file is written by two cpus concurrently, rq_qos may
be added to one disk twice. In that case, there will be two iocs enabled
and running on one disk. They own different iocgs on their active list. In
the ioc_timer_fn function, because of the iocgs from two iocs have the
same root iocg, the root iocg's walk_list may be overwritten by each other
and this leads to list add/del corruptions in building or destroying the
inner_walk list.

And so far, the blk-rq-qos framework works in case that one instance for
one type rq_qos per queue by default. This patch make this explicit and
also fix the crash above.

Signed-off-by: Jinke Han <hanjinke.666@bytedance.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220720093616.70584-1-hanjinke.666@bytedance.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 13 insertions, 7 deletions

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index b7082f2aed9c..7936e5f5821c 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -2886,15 +2886,21 @@ static int blk_iocost_init(struct request_queue *q)
 	 * called before policy activation completion, can't assume that the
 	 * target bio has an iocg associated and need to test for NULL iocg.
 	 */
-	rq_qos_add(q, rqos);
+	ret = rq_qos_add(q, rqos);
+	if (ret)
+		goto err_free_ioc;
+
 	ret = blkcg_activate_policy(q, &blkcg_policy_iocost);
-	if (ret) {
-		rq_qos_del(q, rqos);
-		free_percpu(ioc->pcpu_stat);
-		kfree(ioc);
-		return ret;
-	}
+	if (ret)
+		goto err_del_qos;
 	return 0;
+
+err_del_qos:
+	rq_qos_del(q, rqos);
+err_free_ioc:
+	free_percpu(ioc->pcpu_stat);
+	kfree(ioc);
+	return ret;
 }
 
 static struct blkcg_policy_data *ioc_cpd_alloc(gfp_t gfp)