From: Aaron Tomlin <atomlin@atomlin.com>
To: Wenchao Hao <haowenchao22@gmail.com>
Cc: Wenchao Hao <haowenchao2@huawei.com>, Tejun Heo <tj@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
linux-kernel@vger.kernel.org, neelx@redhat.com
Subject: Re: [RFC PATCH] workqueue: Fix rescuer task's name truncated
Date: Sat, 11 May 2024 15:14:03 +0100 [thread overview]
Message-ID: <qww6bjezmlxic5j2k5hpgjml2266evixfmsrvdkwmypvuzureg@rnuc66f3vskm> (raw)
In-Reply-To: <96888d51-1abb-4a96-ba6d-f84dd1f7245e@gmail.com>
On Wed, Apr 24, 2024 at 11:12:24PM GMT, Wenchao Hao wrote:
> Hi Aaron, thanks a lot for your reply.
No problem.
> I think destroy_workqueue() may not race with wq_worker_comm(),
> wq_pool_attach_mutex is used to avoid race, below is my analysis.
> (Welcome to point out if my understand is incorrect)
>
> t1 which call destroy_workqueue() rescuer->task
>
> destroy_workqueue()
> kthread_stop(rescuer->task)
> rescuer_thread()
> if (should_stop) {
> __set_current_state(TASK_RUNNING);
> set_pf_worker(false);
> mutex_lock(&wq_pool_attach_mutex);
> current->flags &= ~PF_WQ_WORKER;
> mutex_unlock(&wq_pool_attach_mutex);
> return 0;
> }
>
> kfree(rescuer)
>
> wq_worker_comm() would acquire wq_pool_attach_mutex then check if task->flags
> is set PF_WQ_WORKER.
> If PF_WQ_WORKER is not set, wq_worker_comm() would not access this task's worker
> any more;
> If PF_WQ_WORKER is set, the wq_pool_attach_mutex is held durning access of task's
> worker.
Indeed. If I understand correctly then a use-after-free is theoretically
impossible due to the use of the 'wq_pool_attach_mutex' in the context of
rescuer_thread() and wq_pool_attach_mutex(), respectively.
> What confuse me mostly is why the origin logic only append worker's desc when
> worker is attached to a work pool.
I can only assume there was no intention to use the rescuer kworker's
description information for this purpose. Your patch looks fine to me now.
--
Aaron Tomlin
next prev parent reply other threads:[~2024-05-11 14:14 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-23 18:21 [RFC PATCH] workqueue: Fix rescuer task's name truncated Wenchao Hao
2024-04-23 4:55 ` Wenchao Hao
2024-04-24 7:12 ` Aaron Tomlin
2024-04-24 15:12 ` Wenchao Hao
2024-05-11 14:14 ` Aaron Tomlin [this message]
2024-05-11 14:15 ` Aaron Tomlin
2024-05-13 2:28 ` Wenchao Hao
2024-05-13 17:17 ` Tejun Heo
2024-05-14 1:37 ` Wenchao Hao
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