linux-kernel - [tip:sched/urgent] sched: Fix nohz balance kick

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Message-ID: <tip-f6c3f1686e7ec1dd8725a9a3dcb857dfd0c7a5bf@git.kernel.org>
Date:	Tue, 21 Sep 2010 14:13:01 GMT
From:	tip-bot for Suresh Siddha <suresh.b.siddha@...el.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, suresh.b.siddha@...el.com,
	tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/urgent] sched: Fix nohz balance kick

Commit-ID:  f6c3f1686e7ec1dd8725a9a3dcb857dfd0c7a5bf
Gitweb:     http://git.kernel.org/tip/f6c3f1686e7ec1dd8725a9a3dcb857dfd0c7a5bf
Author:     Suresh Siddha <suresh.b.siddha@...el.com>
AuthorDate: Mon, 13 Sep 2010 11:02:21 -0700
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Tue, 21 Sep 2010 13:50:50 +0200

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@...el.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <1284400941.2684.19.camel@...iddha-MOBL3.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched_fair.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

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);
--
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