Commit 985d3a4c authored by Yuyang Du's avatar Yuyang Du Committed by Ingo Molnar

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: default avatarRabin Vincent <rabin.vincent@axis.com>
Signed-off-by: default avatarYuyang Du <yuyang.du@intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150705221151.GF5197@intel.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 63caae84
...@@ -5863,6 +5863,13 @@ static int detach_tasks(struct lb_env *env) ...@@ -5863,6 +5863,13 @@ static int detach_tasks(struct lb_env *env)
return 0; return 0;
while (!list_empty(tasks)) { 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); p = list_first_entry(tasks, struct task_struct, se.group_node);
env->loop++; env->loop++;
......
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