blk-iocost: fix queue stats accounting

The q->stats->accounting is not only used by iocost, but iocost only
increase this counter, never decrease it. So queue stats accounting
will always enabled after using iocost once.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230804070609.31623-1-chengming.zhou@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-iocost.c

@@ -3301,11 +3301,12 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
 	if (qos[QOS_MIN] > qos[QOS_MAX])
 		goto einval;
 
-	if (enable) {
+	if (enable && !ioc->enabled) {
 		blk_stat_enable_accounting(disk->queue);
 		blk_queue_flag_set(QUEUE_FLAG_RQ_ALLOC_TIME, disk->queue);
 		ioc->enabled = true;
-	} else {
+	} else if (!enable && ioc->enabled) {
+		blk_stat_disable_accounting(disk->queue);
 		blk_queue_flag_clear(QUEUE_FLAG_RQ_ALLOC_TIME, disk->queue);
 		ioc->enabled = false;
 	}