From: Yu Kuai <yukuai3@xxxxxxxxxx> request_queue->nr_requests can be changed by: a) switching elevator by update nr_hw_queues b) switching elevator by elevator sysfs attribute c) configue queue sysfs attribute nr_requests Current lock order is: 1) update_nr_hwq_lock, case a,b - allocate elevator tags 2) freeze_queue 3) elevator_lock, cas a,b,c - update nr_requests The update_nr_hwq_lock is not held by case c for now, and we need to check nr_requests while elevator_lock is held, however, we can't allocate elevator_tags whih queue freezed. Hence also require update_nr_hwq_lock and check nr_requests, make it possible to allocate new elevator_tags without queue freezed, also prevent nr_requests to be changed concurrently by other contexts. Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx> --- block/blk-sysfs.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index f3d08edcc34f..37eae7927b45 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -68,13 +68,14 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count) int ret, err; unsigned int memflags; struct request_queue *q = disk->queue; + struct blk_mq_tag_set *set = q->tag_set; ret = queue_var_store(&nr, page, count); if (ret < 0) return ret; - memflags = blk_mq_freeze_queue(q); - mutex_lock(&q->elevator_lock); + /* serialize with switching elevator */ + down_write(&set->update_nr_hwq_lock); if (q->nr_requests == nr) goto unlock; @@ -89,13 +90,17 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count) goto unlock; } + memflags = blk_mq_freeze_queue(q); + mutex_lock(&q->elevator_lock); err = blk_mq_update_nr_requests(disk->queue, nr); if (err) ret = err; -unlock: mutex_unlock(&q->elevator_lock); blk_mq_unfreeze_queue(q, memflags); + +unlock: + up_write(&set->update_nr_hwq_lock); return ret; } -- 2.39.2
