linux-kernel - Re: [PATCH] workqueue: Prevent a new work item from queueing into a destruction wq

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Date:   Sun, 11 Dec 2022 20:23:49 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Richard Clark <richard.xnu.clark@...il.com>
Cc:     jiangshanlai@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: Prevent a new work item from queueing into a
 destruction wq

On Mon, Dec 12, 2022 at 02:18:36PM +0800, Richard Clark wrote:
> Currently the __WQ_DRAINING is used to prevent a new work item from queueing
> to a draining workqueue, but this flag will be cleared before the end of a
> RCU grace period. Because the workqueue instance is actually freed after
> the RCU grace period, this fact results in an opening window in which a new
> work item can be queued into a destorying workqueue and be scheduled
> consequently, for instance, the below code snippet demos this accident:

I mean, this is just use-after-free. The same scenario can happen with
non-RCU frees or if there happens to be an RCU grace period inbetween. I'm
not sure what's being protected here.

Thanks.

-- 
tejun