Messages in this thread |  | | Date | Mon, 10 Feb 2014 14:54:20 +0530 | Subject | Re: [PATCH V2 2/3] sched: Fix race in idle_balance() | From | Preeti Murthy <> |
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HI Daniel,
Isn't the only scenario where another cpu can put an idle task on our runqueue, in nohz_idle_balance() where only the cpus in the nohz.idle_cpus_mask are iterated through. But for the case that this patch is addressing, the cpu in question is not yet a part of the nohz.idle_cpus_mask right?
Any other case would trigger load balancing on the same cpu, but we are preempt_disabled and interrupt disabled at this point.
Thanks
Regards Preeti U Murthy
On Fri, Feb 7, 2014 at 4:40 AM, Daniel Lezcano <daniel.lezcano@linaro.org> wrote: > The scheduler main function 'schedule()' checks if there are no more tasks > on the runqueue. Then it checks if a task should be pulled in the current > runqueue in idle_balance() assuming it will go to idle otherwise. > > But the idle_balance() releases the rq->lock in order to lookup in the sched > domains and takes the lock again right after. That opens a window where > another cpu may put a task in our runqueue, so we won't go to idle but > we have filled the idle_stamp, thinking we will. > > This patch closes the window by checking if the runqueue has been modified > but without pulling a task after taking the lock again, so we won't go to idle > right after in the __schedule() function. > > Cc: alex.shi@linaro.org > Cc: peterz@infradead.org > Cc: mingo@kernel.org > Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> > Signed-off-by: Peter Zijlstra <peterz@infradead.org> > --- > kernel/sched/fair.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 428bc9d..5ebc681 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6589,6 +6589,13 @@ void idle_balance(struct rq *this_rq) > > raw_spin_lock(&this_rq->lock); > > + /* > + * While browsing the domains, we released the rq lock. > + * A task could have be enqueued in the meantime > + */ > + if (this_rq->nr_running && !pulled_task) > + return; > + > if (pulled_task || time_after(jiffies, this_rq->next_balance)) { > /* > * We are going idle. next_balance may be set based on > -- > 1.7.9.5 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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