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Date: Wed, 2 Sep 2009 11:13:40 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Ingo Molnar <mingo@elte.hu>, arjan@infradead.org, jeremy@goop.org,
       mschmidt@redhat.com, mingo@redhat.com, hpa@zytor.com,
       linux-kernel@vger.kernel.org, tj@kernel.org, tglx@linutronix.de,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       linux-tip-commits@vger.kernel.org,
       Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH 0/1] kthreads: simplify !kthreadd_task logic, kill
	kthreadd_task_init_done
Message-ID: <20090902091340.GA5173@redhat.com>
References: <tip-23386d63bbb3199cf247313ec088878d72debcfd@git.kernel.org> <20090901100351.GA3361@elte.hu> <20090901113914.GA23578@elte.hu> <20090901130436.GA22514@redhat.com> <20090901131440.GA29783@elte.hu> <20090901133709.GA24041@redhat.com> <20090901135925.GA9083@elte.hu> <20090901145526.GA31317@redhat.com> <20090901165235.GA9105@redhat.com> <m13a76xnbw.fsf@fess.ebiederm.org>
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On 09/01, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> > On 09/01, Oleg Nesterov wrote:
> >>
> >> On 09/01, Ingo Molnar wrote:
> >> >
> >> > * Oleg Nesterov <oleg@redhat.com> wrote:
> >> >
> >> > > On 09/01, Ingo Molnar wrote:
> >> > > >
> >> > > > * Oleg Nesterov <oleg@redhat.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.