linux-kernel - Re: padata: Is padata_find

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Message-ID: <60778a1e-c29d-4d41-8272-9e635d9ff427@I-love.SAKURA.ne.jp>
Date: Thu, 6 Nov 2025 18:41:19 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: syzbot <syzbot+bd936ccd4339cea66e6b@...kaller.appspotmail.com>,
        daniel.m.jordan@...cle.com, linux-kernel@...r.kernel.org,
        steffen.klassert@...unet.com, linux-crypto@...r.kernel.org
Subject: Re: padata: Is padata_find_next() thread-safe?

On 2025/11/06 18:28, Herbert Xu wrote:
> On Tue, Nov 04, 2025 at 08:44:53PM +0900, Tetsuo Handa wrote:
>> syzbot is reporting possibility of recursive locking at
>> https://syzkaller.appspot.com/bug?extid=bd936ccd4339cea66e6b .
>> If this is a false positive report, the fix will be as simple as
> 
> Yes it's a false positive as reorder->lock is never the same as
> squeue->serial.lock.

OK. But what is about the "Can a sequence shown below possible?" part?

> 
> However, they both have the same data type which is why lockdep
> is confused.
> 
> Please provide a patch that sets the class for one of them to
> something different.  For example, change the lockdep class for
> reorder->lock using lockdep_set_class and the problem should go
> away.

Is using _nested(lock, 1) wrong?