From c48dac137a62a5d6fa1ef3fa445cbd9c43655a76 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Tue, 27 Aug 2019 19:01:45 +0800 Subject: [PATCH] block: don't hold q->sysfs_lock in elevator_init_mq The original comment says: q->sysfs_lock must be held to provide mutual exclusion between elevator_switch() and here. Which is simply wrong. elevator_init_mq() is only called from blk_mq_init_allocated_queue, which is always called before the request queue is registered via blk_register_queue(), for dm-rq or normal rq based driver. However, queue's kobject is only exposed and added to sysfs in blk_register_queue(). So there isn't such race between elevator_switch() and elevator_init_mq(). So avoid to hold q->sysfs_lock in elevator_init_mq(). Cc: Christoph Hellwig Cc: Hannes Reinecke Cc: Greg KH Cc: Mike Snitzer Cc: Bart Van Assche Cc: Damien Le Moal Reviewed-by: Bart Van Assche Signed-off-by: Ming Lei Signed-off-by: Jens Axboe --- block/elevator.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) diff --git a/block/elevator.c b/block/elevator.c index 2f17d66d0e61..33c15fb54ed1 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -607,23 +607,19 @@ int elevator_init_mq(struct request_queue *q) if (q->nr_hw_queues != 1) return 0; - /* - * q->sysfs_lock must be held to provide mutual exclusion between - * elevator_switch() and here. - */ - mutex_lock(&q->sysfs_lock); + WARN_ON_ONCE(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)); + if (unlikely(q->elevator)) - goto out_unlock; + goto out; e = elevator_get(q, "mq-deadline", false); if (!e) - goto out_unlock; + goto out; err = blk_mq_init_sched(q, e); if (err) elevator_put(e); -out_unlock: - mutex_unlock(&q->sysfs_lock); +out: return err; }