linux-kernel - [PATCH v2] keep rd->online and cpu_online

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Message-ID: <20080310215813.10968.960.stgit@novell1.haskins.net>
Date:	Mon, 10 Mar 2008 17:59:11 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	suresh.b.siddha@...el.com
Cc:	ego@...ibm.com, rjw@...k.pl, akpm@...ux-foundation.org,
	dmitry.adamushko@...il.com, ego@...ibm.com, mingo@...e.hu,
	oleg@...sign.ru, yi.y.yang@...el.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, ghaskins@...ell.com
Subject: [PATCH v2] keep rd->online and cpu_online_map in sync

>>> On Mon, Mar 10, 2008 at  6:10 PM, in message
<20080310221014.GB27329@...ux-os.sc.intel.com>, Suresh Siddha
<suresh.b.siddha@...el.com> wrote: 
> On Mon, Mar 10, 2008 at 04:00:28PM -0600, Gregory Haskins wrote:
>> >>> 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:
>> >> >  
>> >> > -	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?
> 
> Yes please.

Here is v2 with the suggested improvement

-Greg

------------------------
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>
Cc: Gautham R Shenoy <ego@...ibm.com>
Cc: "Siddha, Suresh B" <suresh.b.siddha@...el.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: "Rafael J. Wysocki" <rjw@...k.pl>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---

 kernel/sched.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 52b9867..1cb53fb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5881,7 +5881,8 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
 		spin_unlock_irq(&rq->lock);
 		break;
 
-	case CPU_DOWN_PREPARE:
+	case CPU_DYING:
+	case CPU_DYING_FROZEN:
 		/* Update our root-domain */
 		rq = cpu_rq(cpu);
 		spin_lock_irqsave(&rq->lock, flags);

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