linux-kernel - Re: [PATCH v2 2/2] workqueue: ignore dead tasks in a workqueue sleep hook

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Message-ID: <CAJrWOzAZAXapeyd-2KzD6UEMbZhtjv1uGPtQL-sNrP=xTHQ9Hg@mail.gmail.com>
Date:   Mon, 24 Oct 2016 21:09:33 +0200
From:   Roman Penyaev <roman.penyaev@...fitbricks.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] workqueue: ignore dead tasks in a workqueue sleep hook

On Mon, Oct 24, 2016 at 6:40 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Oct 24, 2016 at 06:08:14PM +0200, Roman Pen wrote:
>
>> --- a/kernel/workqueue.c
>> +++ b/kernel/workqueue.c
>> @@ -875,9 +875,31 @@ void wq_worker_waking_up(struct task_struct *task, int cpu)
>>   */
>>  struct task_struct *wq_worker_sleeping(struct task_struct *task)
>>  {
>> -     struct worker *worker = kthread_data(task), *to_wakeup = NULL;
>> +     struct worker *worker, *to_wakeup = NULL;
>>       struct worker_pool *pool;
>>
>> +
>> +     if (task->state == TASK_DEAD)
>> +             /* Here we try to catch the following path before
>> +              * accessing NULL kthread->vfork_done ptr thru
>> +              * kthread_data():
>> +              *
>> +              *    oops_end()
>> +              *    do_exit()
>> +              *    schedule()
>> +              *
>> +              * If panic_on_oops is not set and oops happens on
>> +              * a workqueue execution path, thread will be killed.
>> +              * That is definitly sad, but not to make the situation
>> +              * even worse we have to ignore dead tasks in order not
>> +              * to step on zeroed out members (e.g. t->vfork_done is
>> +              * already NULL on that path, since we were called by
>> +              * do_exit())).
>> +              */
>> +             return NULL;
>
> https://lkml.kernel.org/r/CA+55aFyQYJerovMsSoSKS7PessZBr4vNp-3QUUwhqk4A4_jcbg@mail.gmail.com

Ha, explicit comment from Linus :)  Ok.

> Also, that misses { }.

Ok.

--
Roman