Commit 985d3a4c authored Jul 06, 2015 by Yuyang Du Committed by Ingo Molnar Aug 03, 2015

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 <rabin.vincent@axis.com>
Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Signed-off-by: Peter 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.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 63caae84

kernel/sched/fair.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -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++;

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