From 411654764590c071ef55242ffd50c4e74930353b Mon Sep 17 00:00:00 2001 From: Brendan Jackman Date: Thu, 31 Aug 2017 12:58:01 +0100 Subject: UPSTREAM: sched/fair: Fix usage of find_idlest_group() when no groups are allowed When 'p' is not allowed on any of the CPUs in the sched_domain, we currently return NULL from find_idlest_group(), and pointlessly continue the search on lower sched_domain levels (where 'p' is also not allowed) before returning prev_cpu regardless (as we have not updated new_cpu). Add an explicit check for this case, and add a comment to find_idlest_group(). Now when find_idlest_group() returns NULL, it always means that the local group is allowed and idlest. Change-Id: I5f2648d2f7fb0465677961ecb7473df3d06f0057 Signed-off-by: Brendan Jackman Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Vincent Guittot Reviewed-by: Josef Bacik Cc: Dietmar Eggemann Cc: Josef Bacik Cc: Linus Torvalds Cc: Mike Galbraith Cc: Morten Rasmussen Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20171005114516.18617-5-brendan.jackman@arm.com Signed-off-by: Ingo Molnar (cherry-picked-from: commit 6fee85ccbc76 tip:sched/core) Signed-off-by: Chris Redpath --- kernel/sched/fair.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index dc685b67d08b..0e3a9935515c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5976,6 +5976,8 @@ static unsigned long capacity_spare_wake(int cpu, struct task_struct *p) /* * find_idlest_group finds and returns the least busy CPU group within the * domain. + * + * Assumes p is allowed on at least one CPU in sd. */ static struct sched_group * find_idlest_group(struct sched_domain *sd, struct task_struct *p, @@ -6136,6 +6138,9 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p schedstat_inc(this_rq(), eas_stats.cas_attempts); } + if (!cpumask_intersects(sched_domain_span(sd), &p->cpus_allowed)) + return prev_cpu; + while (sd) { struct sched_group *group; struct sched_domain *tmp; -- cgit v1.2.3