linux-kernel - Re: [PATCH v2] workqueue: Fix double kfree for rescuer

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Message-ID: <bee86d19-6c14-1fd9-eead-24e63af6cf8e@windriver.com>
Date:   Mon, 25 May 2020 18:19:59 +0800
From:   qzhang2 <qiang.zhang@...driver.com>
To:     Markus Elfring <Markus.Elfring@....de>, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2] workqueue: Fix double kfree for rescuer

I see, kfree does nothing with null pointers and direct return.
but again kfree is not a good suggestion.

On 5/25/20 5:50 PM, Markus Elfring wrote:
>> The duplicate memory release should be deleted from the implementation
>> of the callback function "rcu_free_wq".
> 
> I tried to help with the selection of a better commit message.
> I have taken another look also at the implementation of the function “destroy_workqueue”.
> 
> * The function call “destroy_workqueue” can be performed there in an if branch
>    after the statement “wq->rescuer = NULL” was executed.
> 
> * This data processing is independent from a possible call of the
>    function “call_rcu(&wq->rcu, rcu_free_wq)” in another if branch.
>    Thus it seems that a null pointer is intentionally passed by a data structure
>    member to this callback function on demand.
>    The corresponding call of the function “kfree” can tolerate this special case.
> 
> 
> Now I find that the proposed change can be inappropriate.
> 
> Regards,
> Markus
>