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

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Message-Id: <47D5773C.BA47.005A.0@novell.com>
Date:	Mon, 10 Mar 2008 16:00:28 -0600
From:	"Gregory Haskins" <ghaskins@...ell.com>
To:	"Suresh Siddha" <suresh.b.siddha@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	<mingo@...e.hu>, <dmitry.adamushko@...il.com>, <ego@...ibm.com>,
	<yi.y.yang@...el.com>, <tglx@...utronix.de>,
	<akpm@...ux-foundation.org>, <oleg@...sign.ru>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] keep rd->online and cpu_online_map in sync

>>> On Mon, Mar 10, 2008 at  6:03 PM, in message <200803102303.28660.rjw@...k.pl>,
"Rafael J. Wysocki" <rjw@...k.pl> wrote: 
> 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.

Should I add that to the patch as well then?

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


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