linux-kernel - [PATCH -next 1/1] sched/rt: Try to restart rt period timer when rt runtime exceeded

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Date:   Mon, 15 Nov 2021 01:46:28 +0000
From:   Li Hua <hucool.lihua@...wei.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
CC:     <yuehaibing@...wei.com>, <weiyongjun1@...wei.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        <linux-kernel@...r.kernel.org>, <w.f@...wei.com>,
        <hucool.lihua@...wei.com>, <cj.chengjian@...wei.com>,
        <judy.chenhui@...wei.com>
Subject: [PATCH -next 1/1] sched/rt: Try to restart rt period timer when rt runtime exceeded

When rt_runtime is modified from -1 to a valid control value, it may
cause the task to be throttled all the time. Operations like the following
will trigger the bug. E.g:
1. echo -1 > /proc/sys/kernel/sched_rt_runtime_us
2. Run a FIFO task named A that executes while(1)
3. echo 950000 > /proc/sys/kernel/sched_rt_runtime_us

When rt_runtime is -1, The rt period timer will not be activated when task A
enqueued. And then the task will be throttled after setting rt_runtime to
950,000. The task will always be throttled because the rt period timer is not
activated.

Reported-by: Hulk Robot <hulkci@...wei.com>
Signed-off-by: Li Hua <hucool.lihua@...wei.com>
---
 kernel/sched/rt.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index bb945f8faeca..630f2cbe37d0 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -947,6 +947,23 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
+static inline void try_start_rt_bandwidth(struct rt_bandwidth *rt_b)
+{
+	raw_spin_lock(&rt_b->rt_runtime_lock);
+	if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF) {
+		raw_spin_unlock(&rt_b->rt_runtime_lock);
+		return;
+	}
+
+	if (!rt_b->rt_period_active) {
+		rt_b->rt_period_active = 1;
+		hrtimer_forward_now(&rt_b->rt_period_timer, rt_b->rt_period);
+		hrtimer_start_expires(&rt_b->rt_period_timer,
+				      HRTIMER_MODE_ABS_PINNED_HARD);
+	}
+	raw_spin_unlock(&rt_b->rt_runtime_lock);
+}
+
 static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
@@ -1027,11 +1044,16 @@ static void update_curr_rt(struct rq *rq)
 		struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
 
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
+			int exceeded;
+
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			if (sched_rt_runtime_exceeded(rt_rq))
+			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
+			if (exceeded)
+				try_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
 }
@@ -2905,8 +2927,10 @@ static int sched_rt_global_validate(void)
 
 static void sched_rt_do_global(void)
 {
+	raw_spin_lock(&def_rt_bandwidth.rt_runtime_lock);
 	def_rt_bandwidth.rt_runtime = global_rt_runtime();
 	def_rt_bandwidth.rt_period = ns_to_ktime(global_rt_period());
+	raw_spin_unlock(&def_rt_bandwidth.rt_runtime_lock);
 }
 
 int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
-- 
2.17.1