linux-kernel - Re: [PATCH] keep rd->online and cpu_online

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Message-Id: <200803102303.28660.rjw@sisk.pl>
Date:	Mon, 10 Mar 2008 23:03:27 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Gregory Haskins <ghaskins@...ell.com>, ego@...ibm.com,
	akpm@...ux-foundation.org, dmitry.adamushko@...il.com,
	mingo@...e.hu, oleg@...sign.ru, yi.y.yang@...el.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [PATCH] keep rd->online and cpu_online_map in sync

On Monday, 10 of March 2008, Suresh Siddha wrote:
> On Mon, Mar 10, 2008 at 09:39:34AM -0400, Gregory Haskins wrote:
> > keep rd->online and cpu_online_map in sync
> > 
> > It is possible to allow the root-domain cache of online cpus to
> > become out of sync with the global cpu_online_map.  This is because we
> > currently trigger removal of cpus too early in the notifier chain.
> > Other DOWN_PREPARE handlers may in fact run and reconfigure the
> > root-domain topology, thereby stomping on our own offline handling.
> > 
> > The end result is that rd->online may become out of sync with
> > cpu_online_map, which results in potential task misrouting.
> > 
> > So change the offline handling to be more tightly coupled with the
> > global offline process by triggering on CPU_DYING intead of
> > CPU_DOWN_PREPARE.
> > 
> > Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
> > ---
> > 
> >  kernel/sched.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index 52b9867..a616fa1 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -5881,7 +5881,7 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
> >  		spin_unlock_irq(&rq->lock);
> >  		break;
> >  
> > -	case CPU_DOWN_PREPARE:
> > +	case CPU_DYING:
> 
> Don't we need to take care of CPU_DYING_FROZEN aswell?

Well, I'd say we do.

> >  		/* Update our root-domain */
> >  		rq = cpu_rq(cpu);
> >  		spin_lock_irqsave(&rq->lock, flags);
> > 
--
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