linux-kernel - Re: [PATCH] nbd: fix false lockdep deadlock warning

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Message-ID: <c2fbaacc-62a1-4a98-4157-2637b7f242b7@huaweicloud.com>
Date: Sat, 28 Jun 2025 08:48:33 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Ming Lei <ming.lei@...hat.com>, Yu Kuai <yukuai1@...weicloud.com>
Cc: josef@...icpanda.com, axboe@...nel.dk, hch@...radead.org,
 nilay@...ux.ibm.com, hare@...e.de, linux-block@...r.kernel.org,
 nbd@...er.debian.org, linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
 yangerkun@...wei.com, johnny.chenyi@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] nbd: fix false lockdep deadlock warning

Hi,

在 2025/06/27 19:04, Ming Lei 写道:
> I guess the patch in the following link may be simper, both two take
> similar approach:
> 
> https://lore.kernel.org/linux-block/aFjbavzLAFO0Q7n1@fedora/

I this the above approach has concurrent problems if nbd_start_device
concurrent with nbd_start_device:

t1:
nbd_start_device
lock
num_connections = 1
unlock
	t2:
	nbd_add_socket
	lock
	config->num_connections++
	unlock
		t3:
		nbd_start_device
		lock
		num_connections = 2
		unlock
		blk_mq_update_nr_hw_queues

blk_mq_update_nr_hw_queues
//nr_hw_queues updated to 1 before failure
return -EINVAL

Thanks,
Kuai