linux-kernel - Re: [PATCH -rc] workqueue: Reimplement UAF fix to avoid lockdep worning

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Message-ID: <20240604185804.GT3884@unreal>
Date: Tue, 4 Jun 2024 21:58:04 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Tejun Heo <tj@...nel.org>
Cc: Hillf Danton <hdanton@...a.com>, Peter Zijlstra <peterz@...radead.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>, linux-kernel@...r.kernel.org,
	Gal Pressman <gal@...dia.com>, Tariq Toukan <tariqt@...dia.com>,
	RDMA mailing list <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH -rc] workqueue: Reimplement UAF fix to avoid lockdep
 worning

On Tue, Jun 04, 2024 at 06:30:49AM -1000, Tejun Heo wrote:
> Hello, Leon.
> 
> On Tue, Jun 04, 2024 at 02:38:34PM +0300, Leon Romanovsky wrote:
> > Thanks, it is very rare situation where call to flush/drain queue
> > (in our case kthread_flush_worker) in the middle of the allocation
> > flow can be correct. I can't remember any such case.
> >
> > So even we don't fully understand the root cause, the reimplementation
> > is still valid and improves existing code.
> 
> It's not valid. pwq release is async and while wq free in the error path
> isn't. The flush is there so that we finish the async part before
> synchronize error handling. The patch you posted will can lead to double
> free after a pwq allocation failure. We can make the error path synchronous
> but the pwq free path should be updated first so that it stays synchronous
> in the error path. Note that it *needs* to be asynchronous in non-error
> paths, so it's going to be a bit subtle one way or the other.

But at that point, we didn't add newly created WQ to any list which will execute
that asynchronous release. Did I miss something?

Anyway, I understand that the lockdep_register_key() corruption comes
from something else. Do you have any idea what can cause it? How can we
help debug this issue?

Thanks

> 
> Thanks.
> 
> -- 
> tejun
>