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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <197b6dca-56be-438d-a60f-21011367c5ed@linux.ibm.com>
Date: Tue, 1 Jul 2025 18:58:57 +0530
From: Nilay Shroff <nilay@...ux.ibm.com>
To: Yu Kuai <yukuai1@...weicloud.com>, Ming Lei <ming.lei@...hat.com>
Cc: josef@...icpanda.com, axboe@...nel.dk, hch@...radead.org, 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



On 6/28/25 6:18 AM, Yu Kuai wrote:
> 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
> 

In the above case, yes I see that t1 would return -EINVAL (as 
config->num_connections doesn't match with num_connections)
but then t3 would succeed to update nr_hw_queue (as both 
config->num_connections and num_connections set to 2 this 
time). Isn't it? If yes, then the above patch (from Ming)
seems good. 

Thanks,
--Nilay