From: Ming Lei <ming.lei@redhat.com>
Date: Tue, 27 Aug 2019 19:01:45 +0800
Subject: [PATCH] block: don't hold q->sysfs_lock in elevator_init_mq
References: bsc#1156419,jsc#SLE-8281
Git-commit: c48dac137a62a5d6fa1ef3fa445cbd9c43655a76
Patch-mainline: v5.4-rc1
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>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
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;
}
--
2.16.4