linux-kernel - Re: [PATCH v3 1/1] kthread: allocate kthread structure using kmalloc

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Message-ID: <CAJrWOzDK3xt2unUTUZuVrfocvPPfXFtCKqvoxu1OKL76zcf-3w@mail.gmail.com>
Date:   Tue, 25 Oct 2016 17:46:02 +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] kthread: allocate kthread structure using kmalloc

On Tue, Oct 25, 2016 at 4:03 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 10/25, Roman Pen wrote:
>>
>> This patch avoids allocation of kthread structure on a stack, and simply
>> uses kmalloc.
>
> Oh. I didn't even read this patch, but I have to admit I personally do not
> like it. I can be wrong, but imo this is the step to the wrong direction.

it targets only one thing - we can't use stack anymore for keeping kthread
structure on it.  so basically it is not even a step, just an attempt to
fix memory corruption after oops.

> struct kthread is already bloated, we should not bloat it more.

that is clear, but I wanted to keep code simpler with one allocation and
one structure for all the needs.

> Instead we should kill it. And to_kthread() too, at least in its current
> form.

that is nice and this is a step forward, but not with this patch.

>
> For example. parked/exited/cpu should go into smp_hotplug_thread. Yes,
> this needs cleanups.
>
> All we need is kthread_data() which returns the pointer to the private
> data used by kthread.

that means that we still need to store the private data inside task_struct
and probably again abuse some member.

>
> As for kthread_stop(), we no longer need to abuse ->vfork_done, we can
> use task_works:

yes, that can be done easily. in the current patch I already use the
task_work to free the kthread structure. but still for me is not clear
where to keep the private data if you have only task_struct in your
hands.

--
Roman