Re: [PATCH 2/2] kthread: don't use to_live_kthread() in kthread_park() and kthread_unpark()

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/2] kthread: don't use to_live_kthread() in kthread_park() and kthread_unpark()
Date	2016-11-09 18:30 +0100
Message-ID	<sBERc-1R9-21@gated-at.bofh.it> (permalink)
References	(5 earlier) <swBhf-7Ar-5@gated-at.bofh.it> <sxi2R-2c2-3@gated-at.bofh.it> <syr45-75I-11@gated-at.bofh.it> <syr45-75I-17@gated-at.bofh.it> <sBwJY-4WR-27@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 11/09, Thomas Gleixner wrote:
>
> > - watchdog_park_threads() and it does not look nice. The code is actually
> >   correct, get_online_cpus() ensures that kthread_park() can't race with
> >   itself (note that kthread_park() can't handle this race correctly), but
> >   imo it should not use kthread_park() directly.
>
> Should we provide an interface through the smpboot thread infrastructure for
> this?

IMHO yes, I'll write another email.

> I can see why that gpu driver wants to use the park mechanism and I guess
> there are other legitimate use cases as well. I prefer to implement a
> park/unpark variant which is safe to use on arbitrary kthreads

Yes, agreed. Again, I'll write another email. Perhaps we should even keep
park/unpark exported and change them to avoid the races with exit/itself,
I dunno.

My real point was, imo the KTHREAD_IS_PER_CPU/__kthread_bind(kthread->cpu)
logic in kthread_unpark() should be private to smpboot.c/cpu.c.

I'll send another patch tomorrow. kthread_create_worker_on_cpu() ab-uses
this logic too for no reason, but this is trivial.

> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

Thanks!

Probably I should re-send these 2 short series to Ingo with your acks applied.

Oleg.

Thread

[PATCH 0/2] kthread: make struct kthread kmalloc'ed Oleg Nesterov <oleg@redhat.com> - 2016-10-28 18:20 +0200
  [PATCH 1/2] kthread: make struct kthread kmalloc'ed Oleg Nesterov <oleg@redhat.com> - 2016-10-28 18:20 +0200
    Re: [PATCH 1/2] kthread: make struct kthread kmalloc'ed Thomas Gleixner <tglx@linutronix.de> - 2016-10-28 21:00 +0200
  Re: [PATCH 0/2] kthread: make struct kthread kmalloc'ed Thomas Gleixner <tglx@linutronix.de> - 2016-10-28 20:50 +0200
  [PATCH 0/2] kthread: kill to_live_kthread() Oleg Nesterov <oleg@redhat.com> - 2016-10-31 21:10 +0100
    [PATCH 1/2] kthread: don't use to_live_kthread() in kthread_stop() Oleg Nesterov <oleg@redhat.com> - 2016-10-31 21:10 +0100
      Re: [PATCH 1/2] kthread: don't use to_live_kthread() in  kthread_stop() Thomas Gleixner <tglx@linutronix.de> - 2016-11-09 09:10 +0100
    [PATCH 2/2] kthread: don't use to_live_kthread() in kthread_park()  and kthread_unpark() Oleg Nesterov <oleg@redhat.com> - 2016-10-31 21:10 +0100
      Re: [PATCH 2/2] kthread: don't use to_live_kthread() in kthread_park()  and kthread_unpark() Thomas Gleixner <tglx@linutronix.de> - 2016-11-09 09:50 +0100
        Re: [PATCH 2/2] kthread: don't use to_live_kthread() in         kthread_park() and kthread_unpark() Oleg Nesterov <oleg@redhat.com> - 2016-11-09 18:30 +0100
          [PATCH 1/1] kthread: don't abuse kthread_create_on_cpu() in  __kthread_create_worker() Oleg Nesterov <oleg@redhat.com> - 2016-11-10 18:30 +0100
          [PATCH 0/1] kthread: don't abuse kthread_create_on_cpu() in  __kthread_create_worker() Oleg Nesterov <oleg@redhat.com> - 2016-11-10 18:30 +0100
    Re: [PATCH 0/2] kthread: kill to_live_kthread() Andy Lutomirski <luto@amacapital.net> - 2016-11-07 19:40 +0100

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