[tip: sched/core] sched/fair: Refill bandwidth before scaling

[tip-bot2 for Huaixin Chang]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     5a6d6a6ccb5f48ca8cf7c6d64ff83fd9c7999390
Gitweb:        https://git.kernel.org/tip/5a6d6a6ccb5f48ca8cf7c6d64ff83fd9c7999390
Author:        Huaixin Chang <changhuaixin@xxxxxxxxxxxxxxxxx>
AuthorDate:    Mon, 20 Apr 2020 10:44:21 +08:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 30 Apr 2020 20:14:40 +02:00

sched/fair: Refill bandwidth before scaling

In order to prevent possible hardlockup of sched_cfs_period_timer()
loop, loop count is introduced to denote whether to scale quota and
period or not. However, scale is done between forwarding period timer
and refilling cfs bandwidth runtime, which means that period timer is
forwarded with old "period" while runtime is refilled with scaled
"quota".

Move do_sched_cfs_period_timer() before scaling to solve this.

Fixes: 2e8e19226398 ("sched/fair: Limit sched_cfs_period_timer() loop to avoid hard lockup")
Signed-off-by: Huaixin Chang <changhuaixin@xxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Ben Segall <bsegall@xxxxxxxxxx>
Reviewed-by: Phil Auld <pauld@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200420024421.22442-3-changhuaixin@xxxxxxxxxxxxxxxxx
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c0216ef..fac5b2f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5159,6 +5159,8 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
 		if (!overrun)
 			break;
 
+		idle = do_sched_cfs_period_timer(cfs_b, overrun, flags);
+
 		if (++count > 3) {
 			u64 new, old = ktime_to_ns(cfs_b->period);
 
@@ -5188,8 +5190,6 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
 			/* reset count so we don't come right back in here */
 			count = 0;
 		}
-
-		idle = do_sched_cfs_period_timer(cfs_b, overrun, flags);
 	}
 	if (idle)
 		cfs_b->period_active = 0;