linux-kernel - Re: [PATCH v2] lockdep: report name and key when look_up_lock

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Date:   Mon, 19 Sep 2022 22:44:16 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] lockdep: report name and key when look_up_lock_class()
 got confused

On 2022/09/19 19:48, Peter Zijlstra wrote:
> On Mon, Sep 19, 2022 at 09:52:13AM +0900, Tetsuo Handa wrote:
>> Printing this information will be helpful.
>>
>>   ------------[ cut here ]------------
>>   Looking for class "l2tp_sock" with key l2tp_socket_class, but found a different class "slock-AF_INET6" with the same key
>>   WARNING: CPU: 1 PID: 14195 at kernel/locking/lockdep.c:940 look_up_lock_class+0xcc/0x140
>>   Modules linked in:
>>   CPU: 1 PID: 14195 Comm: a.out Not tainted 6.0.0-rc6-dirty #863
>>   Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
>>   RIP: 0010:look_up_lock_class+0xcc/0x140
>>
>> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> 
> Urgh, you hitting that WARN enough times to want to improve it seems to
> suggest your machine is quite sick.

My machine is not sick at all. I just wanted this hint for debugging
https://syzkaller.appspot.com/bug?extid=94cc2a66fc228b23f360 .

In a world of debugging without vmcore, printing as much hint as possible is
important. Therefore, WARN_ONCE() is more appreciated than WARN_ON_ONCE().

> 
> Anyway, patch is ok I suppose.

Thank you. Please send this patch and
https://lkml.kernel.org/r/9f42e8a5-f809-3f2c-0fda-b7657bc94eb3@I-love.SAKURA.ne.jp
via your tree.