BACKPORT: 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.

BACKPORT: Note 4.4 is missing commit 6b94780e45c1 "sched/core: Use
load_avg for selecting idlest group", so we only have to fix
this_load instead of this_runnable_load and this_avg_load.

Change-Id: I41f775b0e7c8f5e675c2780f955bb130a563cba7
Signed-off-by: Brendan Jackman <brendan.jackman@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20171005114516.18617-4-brendan.jackman@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry-picked-from: commit 0d10ab952e99 tip:sched/core)
(backport changes described above)
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

Author: Brendan Jackman

kernel/sched/fair.c

@@ -5983,7 +5983,7 @@ 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_load = ULONG_MAX, this_load = 0;
+	unsigned long min_load = ULONG_MAX, this_load = ULONG_MAX;
 	unsigned long most_spare = 0, this_spare = 0;
 	int load_idx = sd->forkexec_idx;
 	int imbalance = 100 + (sd->imbalance_pct-100)/2;