linux-kernel - Re: [syzbot] [nbd?] possible deadlock in nbd_queue

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Message-ID: <b8769d22-fa19-4374-bbcc-be3f06f420bf@I-love.SAKURA.ne.jp>
Date: Tue, 8 Jul 2025 09:52:18 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Hillf Danton <hdanton@...a.com>, Bart Van Assche <bvanassche@....org>
Cc: axboe@...nel.dk, josef@...icpanda.com, linux-block@...r.kernel.org,
        syzbot <syzbot+3dbc6142c85cc77eaf04@...kaller.appspotmail.com>,
        Ming Lei <ming.lei@...hat.com>, linux-kernel@...r.kernel.org,
        nbd@...er.debian.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [nbd?] possible deadlock in nbd_queue_rq

On 2025/07/08 9:18, Hillf Danton wrote:
> On Mon, 7 Jul 2025 10:39:44 -0700 Bart Van Assche wrote:
>> On 7/6/25 5:59 PM, Hillf Danton wrote:
>>> and given the second one, the report is false positive.
>>
>> Whether or not this report is a false positive, the root cause should be
>> fixed because lockdep disables itself after the first circular locking
>> complaint. From print_usage_bug() in kernel/locking/lockdep.c:
>>
>> 	if (!debug_locks_off() || debug_locks_silent)
>> 		return;
>>
> The root cause could be walked around for example by trying not to init
> nbd more than once.

How did you come to think so?

nbd_init() is already called only once because of module_init(nbd_init).