linux-kernel - [tip:sched/core] sched/fair: Fix find_idlest_group() when local group is not allowed

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Date:   Tue, 10 Oct 2017 04:00:17 -0700
From:   tip-bot for Brendan Jackman <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, josef@...icpanda.com, morten.rasmussen@....com,
        jbacik@...com, dietmar.eggemann@....com, peterz@...radead.org,
        hpa@...or.com, torvalds@...ux-foundation.org,
        vincent.guittot@...aro.org, efault@....de, mingo@...nel.org,
        brendan.jackman@....com, linux-kernel@...r.kernel.org
Subject: [tip:sched/core] sched/fair: Fix find_idlest_group() when local
 group is not allowed

Commit-ID:  0d10ab952e99f3e9f374898e93f45452b81e5711
Gitweb:     https://git.kernel.org/tip/0d10ab952e99f3e9f374898e93f45452b81e5711
Author:     Brendan Jackman <brendan.jackman@....com>
AuthorDate: Thu, 5 Oct 2017 12:45:14 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 10 Oct 2017 11:45:34 +0200

sched/fair: Fix find_idlest_group() when local group is not allowed

When the local group is not allowed we do not modify this_*_load from
their initial value of 0. That means that the load checks at the end
of find_idlest_group cause us to incorrectly return NULL. Fixing the
initial values to ULONG_MAX means we will instead return the idlest
remote group in that case.

Signed-off-by: Brendan Jackman <brendan.jackman@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Reviewed-by: Josef Bacik <jbacik@...com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Josef Bacik <josef@...icpanda.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Morten Rasmussen <morten.rasmussen@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20171005114516.18617-4-brendan.jackman@arm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bdd28fb..cca1835 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5737,8 +5737,9 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
 {
 	struct sched_group *idlest = NULL, *group = sd->groups;
 	struct sched_group *most_spare_sg = NULL;
-	unsigned long min_runnable_load = ULONG_MAX, this_runnable_load = 0;
-	unsigned long min_avg_load = ULONG_MAX, this_avg_load = 0;
+	unsigned long min_runnable_load = ULONG_MAX;
+	unsigned long this_runnable_load = ULONG_MAX;
+	unsigned long min_avg_load = ULONG_MAX, this_avg_load = ULONG_MAX;
 	unsigned long most_spare = 0, this_spare = 0;
 	int load_idx = sd->forkexec_idx;
 	int imbalance_scale = 100 + (sd->imbalance_pct-100)/2;