linux-kernel - Re: 回复: [PATCH v5] workqueue: Remove unnecessary kfree() call in rcu_free

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Message-ID: <CAJhGHyD1nV=M=ccycqCMt86GMuZGkO9trbJ=4ti4EzP9kta6iA@mail.gmail.com>
Date:   Thu, 28 May 2020 20:08:06 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "Zhang, Qiang" <Qiang.Zhang@...driver.com>,
        Markus Elfring <markus.elfring@....de>,
        Tejun Heo <tj@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: 回复: [PATCH v5] workqueue: Remove unnecessary kfree() call in rcu_free_wq()

On Thu, May 28, 2020 at 5:57 PM Dan Carpenter <dan.carpenter@...cle.com> wrote:
>
> Guys, the patch is wrong.  The kfree is harmless when this is called
> from destroy_workqueue() and required when it's called from
> pwq_unbound_release_workfn().  Lai Jiangshan already explained this
> already.  Why are we still discussing this?
>

I'm also confused why they have been debating about the changelog
after the patch was queued. My statement was about "the patch is
a correct cleanup, but the changelog is totally misleading".

destroy_workqueue(percpu_wq) -> rcu_free_wq()
or
destroy_workqueue(unbound_wq) -> put_pwq() ->
pwq_unbound_release_workfn() -> rcu_free_wq()

So the patch is correct to me. Only can destroy_workqueue()
lead to rcu_free_wq().

Still, the kfree(NULL) is harmless. But it is cleaner
to have the patch. But the changelog is wrong, even after
the lengthened debating, and English is not my mother tongue,
so I just looked on.