linux-kernel - Re: [Question] null pointer risk of kernel workqueue

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Date:   Mon, 23 Oct 2017 14:23:17 +0800
From:   tanxiaofei <tanxiaofei@...wei.com>
To:     Li Bin <huawei.libin@...wei.com>, Tejun Heo <tj@...nel.org>
CC:     <jiangshanlai@...il.com>, <linux-kernel@...r.kernel.org>,
        John Garry <john.garry@...wei.com>
Subject: Re: [Question] null pointer risk of kernel workqueue

Hi Bin,

Yes, that's it. thanks.

--
tanxiaofei

On 2017/10/23 9:34, Li Bin wrote:
> 
> 
> on 2017/10/21 23:35, Tejun Heo wrote:
>> On Fri, Oct 20, 2017 at 02:57:18PM +0800, tanxiaofei wrote:
>>> Hi Tejun,
>>>
>>> Any comments about this?
>>
>> I think you're confused, or at least can't understand what you're
>> trying to say.  Can you create a rero?
>>
> 
> Hi Tejun,
> The case is as following:
> 
> 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
>                                                                             |-if (unlikely(wq->flags & __WQ_DRAINING) &&WARN_ON_ONCE(!is_chained_work(wq)))
>                                                                                 |-is_chained_work(wq)
>                                                                                     |-current_wq_worker() // Here, 'current' is the interrupted worker!
>                                                                                         |-current->current_pwq is NULL here!
> |-schedule()
> 
> And I think the following patch can solve the bug, right?
> 
> diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
> index 8635417..650680c 100644
> --- a/kernel/workqueue_internal.h
> +++ b/kernel/workqueue_internal.h
> @@ -59,7 +59,7 @@ struct worker {
>   */
>  static inline struct worker *current_wq_worker(void)
>  {
> -       if (current->flags & PF_WQ_WORKER)
> +       if (!in_irq() && (current->flags & PF_WQ_WORKER))
>                 return kthread_data(current);
>         return NULL;
>  }
> 
> 
> Thanks,
> Li Bin
> 
>> Thanks.
>>
> 
> 
> .
>