linux-kernel - [PATCH] sched/rt: silence double clock update warning by using rq

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Message-Id: <20190815145354.27484-1-pauld@redhat.com>
Date:   Thu, 15 Aug 2019 10:53:54 -0400
From:   Phil Auld <pauld@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: [PATCH] sched/rt: silence double clock update warning by using rq_lock wrappers

With WARN_DOUBLE_CLOCK enabled a false positive warning can occur in rt

        [] rq->clock_update_flags & RQCF_UPDATED
        [] WARNING: CPU: 6 PID: 21426 at kernel/sched/core.c:225 
						update_rq_clock+0x90/0x130
          [] Call Trace:
          []  update_rq_clock+0x90/0x130
          []  sched_rt_period_timer+0x11f/0x340
          []  __hrtimer_run_queues+0x100/0x280
          []  hrtimer_interrupt+0x100/0x220
          []  smp_apic_timer_interrupt+0x6a/0x130
          []  apic_timer_interrupt+0xf/0x20

sched_rt_period_timer does:
                raw_spin_lock(&rq->lock);
                update_rq_clock(rq);

which triggers the warning because of not using the rq_lock wrappers.
So, use the wrappers.

Signed-off-by: Phil Auld <pauld@...hat.com>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Valentin Schneider <valentin.schneider@....com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
---
 kernel/sched/rt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index a532558a5176..0846e71114ee 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -831,6 +831,7 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
 		int enqueue = 0;
 		struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);
 		struct rq *rq = rq_of_rt_rq(rt_rq);
+		struct rq_flags rf;
 		int skip;
 
 		/*
@@ -845,7 +846,7 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
 		if (skip)
 			continue;
 
-		raw_spin_lock(&rq->lock);
+		rq_lock(rq, &rf);
 		update_rq_clock(rq);
 
 		if (rt_rq->rt_time) {
@@ -883,7 +884,7 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
 
 		if (enqueue)
 			sched_rt_rq_enqueue(rt_rq);
-		raw_spin_unlock(&rq->lock);
+		rq_unlock(rq, &rf);
 	}
 
 	if (!throttled && (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF))
-- 
2.18.0