Commit-ID: e5fc66119ec97054eefc83f173a7ee9e133c3c3a
Gitweb: http://git.kernel.org/tip/e5fc66119ec97054eefc83f173a7ee9e133c3c3a
Author: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
AuthorDate: Fri, 17 Jan 2014 10:04:02 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 10 Feb 2014 16:17:04 +0100
sched: Fix race in idle_balance()
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 idle_balance() releases the rq->lock in order to look up 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@xxxxxxxxxx>
Cc: alex.shi@xxxxxxxxxx
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1389949444-14821-2-git-send-email-daniel.lezcano@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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
--
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