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From: Tejun Heo <tj@kernel.org>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Lai Jiangshan <laijs@linux.alibaba.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/4] workqueue: don't check wq->rescuer in rescuer
Date: Fri, 29 May 2020 11:04:34 -0400	[thread overview]
Message-ID: <20200529150434.GF3530656@mtj.duckdns.org> (raw)
In-Reply-To: <CAJhGHyDXrUoOYNMPdqL1ObhCK45LWZj3z7RCjM2KQRKsq5inWg@mail.gmail.com>

Hello,

On Fri, May 29, 2020 at 10:58:46PM +0800, Lai Jiangshan wrote:
> I'm not sure I understood your words. And I'm not
> sure which function may use freed object in "use-after-free".
> Is it "send_mayday() may use a freed rescuer"?
> 
> This patch relies on
> def98c84b6 ("workqueue: Fix spurious sanity check failures in
> destroy_workqueue()")
> to move the kthread_stop() before the sanity check and the work
> of drain_workqueue() which guarantees there is no work item
> in the workqueue. If send_mayday() still goes wrong after
> drain_workqueue(), the user must have queued work items and
> invoked destroy_workqueue() concurrently. It is excellent
> if the sanity check can find this case out, but it is not possible
> that the sanity check can always live through it since it is
> not worqueue's internal fault. We hope the sanity check can
> find all the internal fault, but not to the extend that
> it can always work when any user uses it in a very wrong way.

Yeah, it's not fool proof but it's difficult for me to see what is better
after the patch. What does the patch actually improve?

Thanks.

-- 
tejun

  reply	other threads:[~2020-05-29 15:04 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-29  6:58 [PATCH 0/4] workqueue: simple cleanups Lai Jiangshan
2020-05-29  6:58 ` [PATCH 1/4] workqueue: void unneeded requeuing the pwq in rescuer thread Lai Jiangshan
2020-05-29 14:22   ` Tejun Heo
2020-05-29  6:59 ` [PATCH 2/4] workqueue: don't check wq->rescuer in rescuer Lai Jiangshan
2020-05-29 14:14   ` Tejun Heo
2020-05-29 14:58     ` Lai Jiangshan
2020-05-29 15:04       ` Tejun Heo [this message]
2020-05-29  6:59 ` [PATCH 3/4] workqueue: free wq->unbound_attrs earlier Lai Jiangshan
2020-05-29 14:23   ` Tejun Heo
2020-05-29  6:59 ` [PATCH 4/4] workqueue: remove useless unlock() and lock() in series Lai Jiangshan
2020-05-29 14:26   ` Tejun Heo

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