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

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Message-ID: <20161025161725.GB13257@redhat.com>
Date:   Tue, 25 Oct 2016 18:17:25 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Roman Penyaev <roman.penyaev@...fitbricks.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

Roman, I need to run away, just one note.

On 10/25, Roman Penyaev wrote:
>
> On Tue, Oct 25, 2016 at 5:43 PM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> So in particular I do not understand this comment from the patch above
> where you abuse 'current->set_child_tid':
>
>  * This is the ugly but simple hack we will hopefully remove soon.
>
> how you are going to avoid this abuse of set_child_tid?

please ignore this comment. It actually reflects my desire to kill
struct kthread. If we won't do this, we can (ab)use this or another member
in task_struct.

> or vfork_done?
> because vfork_done is not only for waking up (yes, I totally agree, we
> can reuse task_work), it is also for getting a private data (like
> workqueue uses it):  task_struct->vfork_done->kthread->data.

kthreads simply should not use ->vfork_done at all. to_kthread() can
use the same pointer.

Oleg.