[PATCH] sched/fair: limit burst to zero when cfs bandwidth is toggled off

From: Zhao Wenhui
Date: Tue Aug 09 2022 - 08:06:31 EST


When the quota value in CFS bandwidth is set to -1, that imples the
cfs bandwidth is toggled off. So the burst feature is supposed to
be disable as well.

Currently, when quota is -1, burst will not be check, so that it can be
set to almost arbitery value. Examples:
mkdir /sys/fs/cgroup/cpu/test
echo -1 > /sys/fs/cgroup/cpu/test/cpu.cfs_quota_us
echo 10000000000000000 > /sys/fs/cgroup/cpu/test/cpu.cfs_burst_us

Moreover, after the burst modified by this way, quota can't be set
to any value:
echo 100000 > cpu.cfs_quota_us
-bash: echo: write error: Invalid argument

This patch can ensure the burst value being zero and unalterable,
when quota is set to -1.

Fixes: f4183717b370 ("sched/fair: Introduce the burstable CFS controller")
Reported-by: Zhao Gongyi <zhaogongyi@xxxxxxxxxx>
Signed-off-by: Zhao Wenhui <zhaowenhui8@xxxxxxxxxx>
---
kernel/sched/core.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ee28253c9ac0..4c1fc01d8c68 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10584,6 +10584,12 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota,
burst + quota > max_cfs_runtime))
return -EINVAL;

+ /*
+ * Ensure burst equals to zero when quota is -1.
+ */
+ if (quota == RUNTIME_INF && burst)
+ return -EINVAL;
+
/*
* Prevent race between setting of cfs_rq->runtime_enabled and
* unthrottle_offline_cfs_rqs().
@@ -10643,8 +10649,10 @@ static int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us)

period = ktime_to_ns(tg->cfs_bandwidth.period);
burst = tg->cfs_bandwidth.burst;
- if (cfs_quota_us < 0)
+ if (cfs_quota_us < 0) {
quota = RUNTIME_INF;
+ burst = 0;
+ }
else if ((u64)cfs_quota_us <= U64_MAX / NSEC_PER_USEC)
quota = (u64)cfs_quota_us * NSEC_PER_USEC;
else
--
2.17.1