Messages in this thread Patch in this message | | | Date | Tue, 21 Jan 2014 12:17:56 +0100 | From | Peter Zijlstra <> | Subject | [PATCH 2/9] sched: Fix race in idle_balance() |
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From: Daniel Lezcano <daniel.lezcano@linaro.org>
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> Link: http://lkml.kernel.org/r/1389949444-14821-2-git-send-email-daniel.lezcano@linaro.org --- kernel/sched/fair.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- 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
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