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

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Message-ID: <20090904073749.GB20598@elte.hu>
Date:	Fri, 4 Sep 2009 09:37:49 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>, 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


* Oleg Nesterov <oleg@...hat.com> wrote:

> 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

I dont understand it either - and the .config being !SMP excludes 
any sort of SMP race as well.

Lets delay this until i can debug it more fully.

	Ingo
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