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Subject[PATCH v2] keep rd->online and cpu_online_map in sync
Date
>>> On Mon, Mar 10, 2008 at  6:10 PM, in message
<20080310221014.GB27329@linux-os.sc.intel.com>, Suresh Siddha
<suresh.b.siddha@intel.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@sisk.pl>,
>> "Rafael J. Wysocki" <rjw@sisk.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@novell.com>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Andrew Morton <akpm@linux-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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