From: Jack Wang <jinpu.wang@cloud.ionos.com>
To: gregkh@linuxfoundation.org, sashal@kernel.org, stable@vger.kernel.org
Cc: Ming Lei <ming.lei@redhat.com>,
Christoph Hellwig <hch@infradead.org>,
Hannes Reinecke <hare@suse.com>,
Mike Snitzer <snitzer@redhat.com>,
Bart Van Assche <bvanassche@acm.org>,
Damien Le Moal <damien.lemoal@wdc.com>,
Jens Axboe <axboe@kernel.dk>
Subject: [stable-4.19 2/8] block: don't hold q->sysfs_lock in elevator_init_mq
Date: Wed, 3 Feb 2021 14:20:16 +0100 [thread overview]
Message-ID: <20210203132022.92406-3-jinpu.wang@cloud.ionos.com> (raw)
In-Reply-To: <20210203132022.92406-1-jinpu.wang@cloud.ionos.com>
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;
}
--
2.25.1
next prev parent reply other threads:[~2021-02-03 13:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-03 13:20 [stable-4.19 0/8] Some misc fixes Jack Wang
2021-02-03 13:20 ` [stable-4.19 1/8] block: fix NULL pointer dereference in register_disk Jack Wang
2021-02-03 13:20 ` Jack Wang [this message]
2021-02-03 13:20 ` [stable-4.19 3/8] blk-mq: don't hold q->sysfs_lock in blk_mq_map_swqueue Jack Wang
2021-02-03 13:20 ` [stable-4.19 4/8] block: add helper for checking if queue is registered Jack Wang
2021-02-03 13:20 ` [stable-4.19 5/8] block: split .sysfs_lock into two locks Jack Wang
2021-02-03 13:20 ` [stable-4.19 6/8] block: fix race between switching elevator and removing queues Jack Wang
2021-02-03 13:20 ` [stable-4.19 7/8] block: don't release queue's sysfs lock during switching elevator Jack Wang
2021-02-03 13:20 ` [stable-4.19 8/8] md: Set prev_flush_start and flush_bio in an atomic way Jack Wang
2021-02-04 15:12 ` Greg KH
2021-02-05 6:57 ` Jinpu Wang
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