Received-SPF: pass (google.com: domain of linux-kernel+bounces-200522-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Tue, 4 Jun 2024 14:38:34 +0300
From: Leon Romanovsky <leon@kernel.org>
To: Hillf Danton <hdanton@sina.com>, Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Zqiang <qiang.zhang1211@gmail.com>, linux-kernel@vger.kernel.org,
	Gal Pressman <gal@nvidia.com>, Tariq Toukan <tariqt@nvidia.com>,
	RDMA mailing list <linux-rdma@vger.kernel.org>
Subject: Re: [PATCH -rc] workqueue: Reimplement UAF fix to avoid lockdep
 worning
Message-ID: <20240604113834.GO3884@unreal>
References: <4c4f1fb769a609a61010cb6d884ab2841ef716d3.1716885172.git.leon@kernel.org>
 <ZljyqODpCD0_5-YD@slm.duckdns.org>
 <20240531034851.GF3884@unreal>
 <Zl4jPImmEeRuYQjz@slm.duckdns.org>
 <20240604105456.1668-1-hdanton@sina.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240604105456.1668-1-hdanton@sina.com>

On Tue, Jun 04, 2024 at 06:54:56PM +0800, Hillf Danton wrote:
> On Tue, 4 Jun 2024 11:09:58 +0300 Leon Romanovsky <leon@kernel.org>
> > On Mon, Jun 03, 2024 at 10:10:36AM -1000, Tejun Heo wrote:
> > > 
> > > And KASAN is reporting use-after-free on a completely unrelated VFS object.
> > > I can't tell for sure from the logs alone but lockdep_register_key()
> > > iterates entries in the hashtable trying to find whether the key is a
> > > duplicate and it could be that that walk is triggering the use-after-free
> > > warning. If so, it doesn't really have much to do with workqueue. The
> > > corruption happened elsewhere and workqueue just happens to traverse the
> > > hashtable afterwards.
> > 
> > The problem is that revert of commit 643445531829
> > ("workqueue: Fix UAF report by KASAN in pwq_release_workfn()")
> > fixed these use-after-free reports.
> > 
> Given revert makes sense,

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.

Thanks