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.
Signed-off-by: Daniel Lezcano daniel.lezcano@linaro.org --- kernel/sched/fair.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d601df3..502c51c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6417,6 +6417,13 @@ 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