[tip:sched/core] sched: Fix load avg vs. cpu-hotplug

[tip-bot for Peter Zijlstra <peterz@infradead.org>]

Commit-ID:  08bedae1d0acd8c9baf514fb69fa199d0c8345f6
Gitweb:     http://git.kernel.org/tip/08bedae1d0acd8c9baf514fb69fa199d0c8345f6
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 6 Sep 2012 00:03:50 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 13 Sep 2012 16:52:05 +0200

sched: Fix load avg vs. cpu-hotplug

Commit f319da0c68 ("sched: Fix load avg vs cpu-hotplug") was an
incomplete fix:

In particular, the problem is that at the point it calls
calc_load_migrate() nr_running := 1 (the stopper thread), so move the
call to CPU_DEAD where we're sure that nr_running := 0.

Also note that we can call calc_load_migrate() without serialization, we
know the state of rq is stable since its cpu is dead, and we modify the
global state using appropriate atomic ops.

Suggested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1346882630.2600.59.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8b51b2d..ba144b1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5048,7 +5048,9 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
 		migrate_tasks(cpu);
 		BUG_ON(rq->nr_running != 1); /* the migration thread */
 		raw_spin_unlock_irqrestore(&rq->lock, flags);
+		break;
 
+	case CPU_DEAD:
 		calc_load_migrate(rq);
 		break;
 #endif