linux-kernel - [PATCH 2/2] keep rd->online and cpu_online

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Date:	Mon, 10 Mar 2008 16:52:46 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	unlisted-recipients:; (no To-header on input)
Cc:	linux-kernel@...r.kernel.org, ghaskins@...ell.com,
	Gregory Haskins <ghaskins@...ell.com>
Subject: [PATCH 2/2] 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 |    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:
 		/* Update our root-domain */
 		rq = cpu_rq(cpu);
 		spin_lock_irqsave(&rq->lock, flags);

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