[PATCH 5.4 075/320] sched/rt: Try to restart rt period timer when rt runtime exceeded

Greg Kroah-Hartman
2022-01-24T20:01:18Z

From: Li Hua <hucool.lihua@huawei.com>

[ Upstream commit 9b58e976b3b391c0cf02e038d53dd0478ed3013c ]

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.

Fixes: d0b27fa77854 ("sched: rt-group: synchonised bandwidth period")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Li Hua <hucool.lihua@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211203033618.11895-1-hucool.lihua@huawei.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/sched/rt.c | 23 ++++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 2dffb8762e16b..28c82dee13ea9 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -52,11 +52,8 @@ void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime)
rt_b->rt_period_timer.function = sched_rt_period_timer;
}

-static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
+static inline void do_start_rt_bandwidth(struct rt_bandwidth *rt_b)
{
- if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
- return;
-
raw_spin_lock(&rt_b->rt_runtime_lock);
if (!rt_b->rt_period_active) {
rt_b->rt_period_active = 1;
@@ -75,6 +72,14 @@ static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
raw_spin_unlock(&rt_b->rt_runtime_lock);
}

+static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
+{
+ if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
+ return;
+
+ do_start_rt_bandwidth(rt_b);
+}
+
void init_rt_rq(struct rt_rq *rt_rq)
{
struct rt_prio_array *array;
@@ -983,13 +988,17 @@ static void update_curr_rt(struct rq *rq)

for_each_sched_rt_entity(rt_se) {
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
+ int exceeded;

if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
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)
+ do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
}
}
}
@@ -2659,8 +2668,12 @@ static int sched_rt_global_validate(void)

static void sched_rt_do_global(void)
{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
def_rt_bandwidth.rt_runtime = global_rt_runtime();
def_rt_bandwidth.rt_period = ns_to_ktime(global_rt_period());
+ raw_spin_unlock_irqrestore(&def_rt_bandwidth.rt_runtime_lock, flags);
}

int sched_rt_handler(struct ctl_table *table, int write,
--
2.34.1