linux-kernel - Re: [PATCH/RFC] sched: Remove SYSTEM_RUNNING checks from cond

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Message-Id: <1247057926.9777.54.camel@twins>
Date:	Wed, 08 Jul 2009 14:58:46 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	avorontsov@...mvista.com
Cc:	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC] sched: Remove SYSTEM_RUNNING checks from
 cond_resched*()

On Wed, 2009-07-08 at 16:55 +0400, Anton Vorontsov wrote:
> On Wed, Jul 08, 2009 at 02:12:25PM +0200, Peter Zijlstra wrote:
> > On Wed, 2009-07-08 at 16:03 +0400, Anton Vorontsov wrote:
> > > On Wed, Jul 08, 2009 at 08:24:23AM +0200, Peter Zijlstra wrote:
> > > > On Wed, 2009-07-08 at 02:50 +0200, Oleg Nesterov wrote:
> > > > 
> > > > > 	/*
> > > > > 	 * It is valid to assume CPU-locality during early bootup:
> > > > > 	 */
> > > > > 	if (system_state != SYSTEM_RUNNING)
> > > > > 		goto out;
> > > > > 
> > > > > this doesn't look right, smp_init() is called before we set
> > > > > SYSTEM_RUNNING.
> > > > 
> > > > The thing is, there's also ton's of code that might end up calling
> > > > cond_resched() and co before the scheduler is fully initialized.
> > > 
> > > Hm. Speaking of cond_resched*() only, then it should be pretty
> > > safe to convert the SYSTEM_RUNNING checks to scheduler_running,
> > > no? scheduler_running is set after sched_init().
> > 
> > Hmm, that might work, I'd have to audit sched_init_smp() as it seems to
> > do way too much...
> 
> sched_init_smp() is called from the kernel_thread(), so
> if the scheduler is not functional prior to kernel_thread(),
> you're in trouble anyway, no? The point is that a lot of
> code is calling schedule() prior to sched_init_smp()
> (e.g. msleep(), mutexes), and there are no issues. So
> should be no issues with cond_resched()?

Yeah, it should be good, I just got paranoid looking at
sched_init_smp().

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