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block: don't hold q->sysfs_lock in elevator_init_mq

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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>
This commit is contained in:
Ming Lei 2019-08-27 19:01:45 +08:00 committed by Jens Axboe
parent 9685b22702
commit c48dac137a
1 changed files with 5 additions and 9 deletions
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14
block/elevator.c
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@ -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;
}