linux-kernel - Re: [PATCH 0/1] kthreads: simplify !kthreadd_task logic, kill kthreadd_task_init

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Message-ID: <20090902091340.GA5173@redhat.com>
Date:	Wed, 2 Sep 2009 11:13:40 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Ingo Molnar <mingo@...e.hu>, arjan@...radead.org, jeremy@...p.org,
	mschmidt@...hat.com, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, tj@...nel.org, tglx@...utronix.de,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-tip-commits@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 0/1] kthreads: simplify !kthreadd_task logic, kill
	kthreadd_task_init_done

On 09/01, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> > On 09/01, Oleg Nesterov wrote:
> >>
> >> On 09/01, Ingo Molnar wrote:
> >> >
> >> > * Oleg Nesterov <oleg@...hat.com> wrote:
> >> >
> >> > > On 09/01, Ingo Molnar wrote:
> >> > > >
> >> > > > * Oleg Nesterov <oleg@...hat.com> wrote:
> >> > > >
> >> > > > > Yes, this should work. But I _think_ we can make the better fix...
> >> > > > >
> >> > > > > I'll try to make the patch soon. Afaics we don't need
> >> > > > > kthreadd_task_init_done.
> >> > > >
> >> > > > ok.
> >> > >
> >> > > Just in case, the patch is ready. [...]
> >> >
> >> > yes - that's roughly the cleanup i referred to in the commit log.
> >> >
> >> > way too late for -rc8 though - the minimal fix i did _might_ be
> >> > eligible.
> >> >
> >> > agreed?
> >>
> >> Agreed. Then I will sent the patch on top of this change.
> >
> > OK, I am sending the patch on top of your fix. Not sure how to really
> > test it, but at least the kernel works when I apply the debugging patch
> > below on top.
>
> Stupid question.  How is it that we wind up trying to start kernel threads
> before it is safe to do so?
>
> Races should be impossible because the scheduler isn't running until a few
> lines later.

Yes, I am confused too.

At first I thought I understand the race, now I don't. Please see the whole
thread: http://marc.info/?t=125180592500005

Oleg.

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