From 985d3a4c11cd28251bcc7925aa2d7a9038910384 Mon Sep 17 00:00:00 2001 From: Yuyang Du Date: Mon, 6 Jul 2015 06:11:51 +0800 Subject: [PATCH] sched/fair: Avoid pulling all tasks in idle balancing In idle balancing where a CPU going idle pulls tasks from another CPU, a livelock may happen if the CPU pulls all tasks from another, makes it idle, and this iterates. So just avoid this. Reported-by: Rabin Vincent Signed-off-by: Yuyang Du Signed-off-by: Peter Zijlstra (Intel) Cc: Ben Segall Cc: Linus Torvalds Cc: Mike Galbraith Cc: Mike Galbraith Cc: Morten Rasmussen Cc: Paul Turner Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20150705221151.GF5197@intel.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 587a2f67ceb1..8b384b8d2f1d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5863,6 +5863,13 @@ static int detach_tasks(struct lb_env *env) return 0; while (!list_empty(tasks)) { + /* + * We don't want to steal all, otherwise we may be treated likewise, + * which could at worst lead to a livelock crash. + */ + if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1) + break; + p = list_first_entry(tasks, struct task_struct, se.group_node); env->loop++; -- 2.34.1