linux-kernel - Re: [PATCH] workqueue: Fix NULL pointer dereference

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Date:   Tue, 24 Oct 2017 07:45:46 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Li Bin <huawei.libin@...wei.com>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, tanxiaofei@...wei.com,
        guohanjun@...wei.com
Subject: Re: [PATCH] workqueue: Fix NULL pointer dereference

On Tue, Oct 24, 2017 at 09:18:34AM +0800, Li Bin wrote:
> When queue_work() is used in irq handler, there is a potential
> case that trigger NULL pointer dereference.
> ----------------------------------------------------------------
> worker_thread()
> |-spin_lock_irq()
> |-process_one_work()
> 	|-worker->current_pwq = pwq
> 	|-spin_unlock_irq()
> 	|-worker->current_func(work)
> 	|-spin_lock_irq()
>  	|-worker->current_pwq = NULL
> |-spin_unlock_irq()
> 
> 				//interrupt here
> 				|-irq_handler
> 					|-__queue_work()
> 						//assuming that the wq is draining
> 						|-is_chained_work(wq)
> 							|-current_wq_worker()
> 							//Here, 'current' is the interrupted worker!
> 								|-current->current_pwq is NULL here!
> |-schedule()
> ----------------------------------------------------------------
> 
> Avoid it by checking for irq context in current_wq_worker(), and
> if in irq context, we shouldn't use the 'current' to check the
> condition.
> 
> Reported-by: Xiaofei Tan <tanxiaofei@...wei.com>
> Signed-off-by: Li Bin <huawei.libin@...wei.com>

Applied to wq/for-4.14-fixes.

Thanks.

-- 
tejun