From: Mike Galbraith <efault@gmx.de>
Date: Fri, 4 May 2018 08:14:38 +0200
Subject: sched/fair: Fix CFS bandwidth control lockdep DEADLOCK report
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 8aed28394e4fd2640da85aa2a16bbf24a444c919
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

[ Upstream commit df7e8acc0c9a84979a448d215b8ef889efe4ac5a ]

CFS bandwidth control yields the inversion gripe below, moving
handling quells it.

|========================================================
|WARNING: possible irq lock inversion dependency detected
|4.16.7-rt1-rt #2 Tainted: G            E
|--------------------------------------------------------
|sirq-hrtimer/0/15 just changed the state of lock:
| (&cfs_b->lock){+...}, at: [<000000009adb5cf7>] sched_cfs_period_timer+0x28/0x140
|but this lock was taken by another, HARDIRQ-safe lock in the past: (&rq->lock){-...}
|and interrupts could create inverse lock ordering between them.
|other info that might help us debug this:
| Possible interrupt unsafe locking scenario:
|       CPU0                    CPU1
|       ----                    ----
|  lock(&cfs_b->lock);
|                               local_irq_disable();
|                               lock(&rq->lock);
|                               lock(&cfs_b->lock);
|  <Interrupt>
|    lock(&rq->lock);

Cc: stable-rt@vger.kernel.org
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 kernel/sched/fair.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5031,9 +5031,9 @@ void init_cfs_bandwidth(struct cfs_bandw
 	cfs_b->period = ns_to_ktime(default_cfs_period());
 
 	INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
-	hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
+	hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
 	cfs_b->period_timer.function = sched_cfs_period_timer;
-	hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
 	cfs_b->slack_timer.function = sched_cfs_slack_timer;
 }