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From: tanxiaofei <tanxiaofei@huawei.com>
To: <tj@kernel.org>, <jiangshanlai@gmail.com>,
	<linux-kernel@vger.kernel.org>
Cc: Linuxarm <linuxarm@huawei.com>
Subject: [Question] null pointer risk of kernel workqueue
Date: Sat, 23 Sep 2017 17:04:24 +0800	[thread overview]
Message-ID: <59C62398.6040101@huawei.com> (raw)

Hi Tejun & Jiangshan,

I find an null pointer risk in the code of workqueue. Here is description:

If draining, __queue_work() will call the function is_chained_work() to do some checks.
In is_chained_work(), worker->current_pwq is used directly. It should be not safe.
http://elixir.free-electrons.com/linux/latest/source/kernel/workqueue.c#L1384

If you check the thread function of this worker, worker_thread(), you will find worker->current_pwq
is null when one work is done or ready to be processed.
This issue may happen only if we queue work during executing drain_workqueue().
http://elixir.free-electrons.com/linux/latest/source/kernel/workqueue.c#L2173

There are very few places to call drain_workqueue() in the whole linux kernel.
I think that's why no one noticed this risk.

Xiaofei Tan
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.

             reply	other threads:[~2017-09-23  9:05 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-23  9:04 tanxiaofei [this message]
2017-09-25 15:25 ` [Question] null pointer risk of kernel workqueue Tejun Heo
2017-09-27  9:17   ` tanxiaofei
2017-10-20  6:57     ` tanxiaofei
2017-10-21 15:35       ` Tejun Heo
2017-10-21 15:35         ` Tejun Heo
2017-10-23  1:34         ` Li Bin
2017-10-23  6:23           ` tanxiaofei
2017-10-23 14:03           ` Tejun Heo
2017-10-24  0:33             ` Li Bin

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