linux-kernel - Re: [PATCH v3 1/1] workqueue: ignore dead tasks in a workqueue sleep hook

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Message-ID: <CAJrWOzCfjYHtJQFQ+YUmTk3jNmsOtxDMSqTDWqWs5YQPMborbg@mail.gmail.com>
Date:   Tue, 25 Oct 2016 20:15:56 +0200
From:   Roman Penyaev <roman.penyaev@...fitbricks.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] workqueue: ignore dead tasks in a workqueue sleep hook

On Tue, Oct 25, 2016 at 6:08 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> sorry for noise, forgot to mention...
>
> On 10/25, Oleg Nesterov wrote:
>>
>> On 10/25, Oleg Nesterov wrote:
>> >
>> >     void oops_end_exit(void)
>> >     {
>> >             current->flags &= ~PF_WQ_WORKER;
>> >             perhaps sonething else;
>> >     }
>> >
>> > called by oops_end() before rewind_stack_do_exit() ?
>>
>> and "perhaps sonething else" above should probably clear current->plug,
>> it likely points to "struct blk_plug" on stack.
>>
>> and perhaps call task_work_run(). Currently only irq_thread() uses the
>> "destructor" work on stack, but think can have more users.
>
> and, probably absorb some code from do_exit(), say set_fs(USER_DS) and/or
> PF_EXITING check.

I agree that for stack which was rewound we need more cleanups.  But in the
current patch I do not want to mix several cases.  Here I try to avoid access
to a NULL pointer of a dead task.  That is not related to a corrupted stack.

Regarding the PF_WQ_WORKER flags.  I liked the idea that workqueue itself
should be able to detect that task is dead.  Spreading the code which does
flags cleanup for a special workqueue case IMO is not nice.

And, indeed, PF_EXITING looks more generic.  Thanks.  I will resend this.

--
Roman