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Date:   Thu, 26 Oct 2017 23:55:00 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Li Bin <huawei.libin@...wei.com>
Cc:     Tejun Heo <tj@...nel.org>, LKML <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 9:18 AM, Li Bin <huawei.libin@...wei.com> 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!

I remember that softirq can be invoked when irq_eixt(),
and in this case the current->current_pwq is also NULL
if __queue_work() is called in the soft irq.

So in_task() might be better than !in_irq() for the fix?

> |-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>
> ---
>  kernel/workqueue_internal.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
> index 8635417..d81cb9b 100644
> --- a/kernel/workqueue_internal.h
> +++ b/kernel/workqueue_internal.h
> @@ -9,6 +9,7 @@
>
>  #include <linux/workqueue.h>
>  #include <linux/kthread.h>
> +#include <linux/preempt.h>
>
>  struct worker_pool;
>
> @@ -59,7 +60,7 @@ 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;
>  }
> --
> 1.7.12.4
>

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