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From: Suresh Siddha <>
Date: Mon, 13 Sep 2010 18:02:21 +0000 (-0700)
Subject: sched: Fix nohz balance kick

sched: Fix nohz balance kick

There's a situation where the nohz balancer will try to wake itself:

cpu-x is idle which is also ilb_cpu
got a scheduler tick during idle
and the nohz_kick_needed() in trigger_load_balance() checks for
rq_x->nr_running which might not be zero (because of someone waking a
task on this rq etc) and this leads to the situation of the cpu-x
sending a kick to itself.

And this can cause a lockup.

Avoid this by not marking ourself eligible for kicking.

Signed-off-by: Suresh Siddha <>
Signed-off-by: Peter Zijlstra <>
LKML-Reference: <>
Signed-off-by: Ingo Molnar <>

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index a171138..db3f674 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3630,7 +3630,7 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
 	if (time_before(now, nohz.next_balance))
 		return 0;
-	if (!rq->nr_running)
+	if (rq->idle_at_tick)
 		return 0;
 	first_pick_cpu = atomic_read(&nohz.first_pick_cpu);