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Subject[PATCH v3 5/5] sched/fair: Fix use of find_idlest_group when local group is idlest
find_idlest_group returns NULL when the local group is idlest. The
caller then continues the find_idlest_group search at a lower level
of the current CPU's sched_domain hierarchy. find_idlest_group_cpu is
not consulted and, crucially, @new_cpu is not updated. This means the
search is pointless and we return @prev_cpu from select_task_rq_fair.

This is fixed by initialising @new_cpu to @cpu instead of

Signed-off-by: Brendan Jackman <>
Cc: Dietmar Eggemann <>
Cc: Vincent Guittot <>
Cc: Josef Bacik <>
Cc: Ingo Molnar <>
Cc: Morten Rasmussen <>
Cc: Peter Zijlstra <>
kernel/sched/fair.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2608091..f93cb97 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5567,7 +5567,7 @@ find_idlest_group_cpu(struct sched_group *group, struct task_struct *p, int this
static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p,
int cpu, int prev_cpu, int sd_flag)
- int new_cpu = prev_cpu;
+ int new_cpu = cpu;

if (!cpumask_intersects(sched_domain_span(sd), &p->cpus_allowed))
return prev_cpu;
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