[PATCH] sched: fix rt-bandwidth hotplug race

[Peter Zijlstra <peterz@infradead.org>]

Subject: sched: fix rt-bandwidth hotplug race
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Thu Aug 14 15:42:44 CEST 2008

When we hot-unplug a cpu and rebuild the sched-domain, all cpus will be
detatched. Alex observed the case where a runqueue was stealing bandwidth
from an already disabled runqueue to satisfy its own needs.

Stop this by skipping over already disabled runqueues.

Reported-by: Alex Nixon <alex.nixon@citrix.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Alex Nixon <alex.nixon@citrix.com>
---
 kernel/sched_rt.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/kernel/sched_rt.c
===================================================================
--- linux-2.6.orig/kernel/sched_rt.c
+++ linux-2.6/kernel/sched_rt.c
@@ -298,7 +298,7 @@ static void __disable_runtime(struct rq 
 			struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
 			s64 diff;
 
-			if (iter == rt_rq)
+			if (iter == rt_rq || iter->rt_runtime == RUNTIME_INF)
 				continue;
 
 			spin_lock(&iter->rt_runtime_lock);