Messages in this thread Patch in this message | | | Date | Mon, 6 Jul 2015 06:11:51 +0800 | From | Yuyang Du <> | Subject | Re: [PATCH?] Livelock in pick_next_task_fair() / idle_balance() |
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On Fri, Jul 03, 2015 at 06:39:28PM +0200, Peter Zijlstra wrote: > On Thu, Jul 02, 2015 at 07:25:11AM +0800, Yuyang Du wrote: > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 40a7fcb..f7cc1ef 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -5898,6 +5898,10 @@ static int detach_tasks(struct lb_env *env) > > return 0; > > > > while (!list_empty(tasks)) { > > + > > + if (env->idle == CPU_NEWLY_IDLE && env->src_rq->nr_running <= 1) > > Should we make that ->idle != CPU_NOT_IDLE ?
I think including CPU_IDLE is good.
-- Subject: [PATCH] sched: 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> --- kernel/sched/fair.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 40a7fcb..769d591 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5898,6 +5898,13 @@ 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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