linux-kernel - Re: [PATCH v3] workqueue: Fix double kfree for rescuer

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Date:   Tue, 26 May 2020 16:56:19 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     qiang.zhang@...driver.com
Cc:     Tejun Heo <tj@...nel.org>, markus.elfring@....de,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] workqueue: Fix double kfree for rescuer

On Mon, May 25, 2020 at 5:22 PM <qiang.zhang@...driver.com> wrote:
>
> From: Zhang Qiang <qiang.zhang@...driver.com>
>
> The callback function "rcu_free_wq" could be called after memory
> was released for "rescuer" already, Thus delete a misplaced call
> of the function "kfree".

Hello

wq->rescuer is guaranteed to be NULL in rcu_free_wq()
since def98c84b6cd
("workqueue: Fix spurious sanity check failures in destroy_workqueue()")

And the resucer is already free in destroy_workqueue()
since 8efe1223d73c
("workqueue: Fix missing kfree(rescuer) in destroy_workqueue()")

The patch is a cleanup to remove a "kfree(NULL);".
But the changelog is misleading.

>
> Fixes: 6ba94429c8e7 ("workqueue: Reorder sysfs code")

It is totally unrelated.

> Signed-off-by: Zhang Qiang <qiang.zhang@...driver.com>
> ---
>  v1->v2->v3:
>  Only commit information modification.
>  kernel/workqueue.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 891ccad5f271..a2451cdcd503 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -3491,7 +3491,6 @@ static void rcu_free_wq(struct rcu_head *rcu)
>         else
>                 free_workqueue_attrs(wq->unbound_attrs);
>
> -       kfree(wq->rescuer);
>         kfree(wq);
>  }
>
> --
> 2.24.1
>