linux-kernel - Re: [PATCH] workqueue: Fix double kfree(rescuer) in destroy

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Date:   Mon, 25 May 2020 14:43:31 +0800
From:   qzhang2 <qiang.zhang@...driver.com>
To:     Markus Elfring <Markus.Elfring@....de>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Tejun Heo <tj@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] workqueue: Fix double kfree(rescuer) in
 destroy_workqueue()

Sorry I didn't describe clearly

I describe the meaning as follows:

  destroy_workqueue:
	if(wq->rescuer)
		struct worker *rescuer = wq->rescuer
		kfree(rescuer)  //first kfree
		

         if (!(wq->flags & WQ_UNBOUND))
		call_rcu(&wq->rcu, rcu_free_wq)
			
		rcu_free_wq
			kfree(wq->rescuer) //second kfree

there are double free.

On 5/24/20 11:33 PM, Markus Elfring wrote:
>> When destroy_workqueue if rescuer worker exist,wq->rescuer pointer be
>> kfree. if sanity checks passed. the func call_rcu(&wq->rcu, rcu_free_wq)
>> will be called if the wq->flags & WQ_UNBOUND is false,in rcu_free_wq
>> func wq->rescuer pointer was kfree again.
> 
> 1. I suggest to improve also this change description.
>     Do you try to explain here that a call of the function “free_workqueue_attrs”
>     (or “free_percpu”) would perform sufficient clean-up of system resources
>     in this use case?
> 
> 2. You proposed to delete the function call “kfree(wq->rescuer)” from
>     the implementation of the function “rcu_free_wq”.
>     https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/kernel/workqueue.c?id=c11d28ab4a691736e30b49813fb801847bd44e83#n3482
>     https://elixir.bootlin.com/linux/v5.7-rc6/source/kernel/workqueue.c#L3482
> 
>     This function name should be specified also in the patch subject,
>     shouldn't it?
> 
> 3. Would you like to add the tag “Fixes” to the commit message?
> 
> Regards,
> Markus
>