From: Ming Lei ming.lei@redhat.com
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 hch@infradead.org Cc: Hannes Reinecke hare@suse.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Mike Snitzer snitzer@redhat.com Cc: Bart Van Assche bvanassche@acm.org Cc: Damien Le Moal damien.lemoal@wdc.com Reviewed-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk (cherry picked from commit c48dac137a62a5d6fa1ef3fa445cbd9c43655a76) Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- block/elevator.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/block/elevator.c b/block/elevator.c index fae58b2f906f..ddbcd36616a8 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -980,23 +980,19 @@ 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; }