block: don't hold q->sysfs_lock in elevator_init_mq
authorMing Lei <ming.lei@redhat.com>
Tue, 27 Aug 2019 11:01:45 +0000 (19:01 +0800)
committerJens Axboe <axboe@kernel.dk>
Tue, 27 Aug 2019 16:40:20 +0000 (10:40 -0600)
commitc48dac137a62a5d6fa1ef3fa445cbd9c43655a76
tree0cbc830e7a790655bb0d012ca555f24852765fb3
parent9685b2270211628e27ea7880a02b52efd4524099
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 <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>
block/elevator.c