From: Suresh Siddha <suresh.b.siddha@intel.com>

Date: Mon, 13 Sep 2010 18:02:21 +0000 (-0700)

Subject: sched: Fix nohz balance kick

X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=f6c3f1686e7ec1dd8725a9a3dcb857dfd0c7a5bf

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 <suresh.b.siddha@intel.com>

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

LKML-Reference: <1284400941.2684.19.camel@sbsiddha-MOBL3.sc.intel.com>

Signed-off-by: Ingo Molnar <mingo@elte.hu>

---

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);