linux-kernel - [PATCH] sched/core: fix incorrect parameter burst in cpu_max

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Date: Wed, 24 Apr 2024 21:24:38 +0800
From: Cheng Yu <serein.chengyu@...wei.com>
To: <mingo@...hat.com>, <peterz@...radead.org>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
	<bristot@...hat.com>, <vschneid@...hat.com>,
	<changhuaixin@...ux.alibaba.com>, <shanpeic@...ux.alibaba.com>,
	<dtcccc@...ux.alibaba.com>, <tj@...nel.org>, <linux-kernel@...r.kernel.org>
CC: <zhangqiao22@...wei.com>, <judy.chenhui@...wei.com>,
	<yusongping@...wei.com>, <serein.chengyu@...wei.com>
Subject: [PATCH] sched/core: fix incorrect parameter burst in cpu_max_write()

In the cgroup v2 cpu subsystem, assuming we have a
cgroup named test, we set cpu.max and cpu.max.burst:
    # echo 1000000 > /sys/fs/cgroup/test/cpu.max
    # echo 1000000 > /sys/fs/cgroup/test/cpu.max.burst
then we check cpu.max and cpu.max.burst:
    # cat /sys/fs/cgroup/test/cpu.max
    1000000 100000
    # cat /sys/fs/cgroup/test/cpu.max.burst
    1000000

Next we set cpu.max again and check cpu.max and
cpu.max.burst:
    # echo 2000000 > /sys/fs/cgroup/test/cpu.max
    # cat /sys/fs/cgroup/test/cpu.max
    2000000 100000
    # cat /sys/fs/cgroup/test/cpu.max.burst
    1000
we found that the cpu.max.burst value changed unexpectedly.

In cpu_max_write(), the unit of the burst value returned
by tg_get_cfs_burst() is microseconds, while in cpu_max_write(),
the burst unit used for calculation should be nanoseconds,
which leads to the bug.

To fix it, we get the burst value directly from
tg->cfs_bandwidth.burst.

Reported-by: Qixin Liao <liaoqixin@...wei.com>
Fixes: f4183717b370 ("sched/fair: Introduce the burstable CFS controller")
Signed-off-by: Cheng Yu <serein.chengyu@...wei.com>
Signed-off-by: Zhang Qiao <zhangqiao22@...wei.com>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7019a40457a6..d211d40a2edc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11402,7 +11402,7 @@ static ssize_t cpu_max_write(struct kernfs_open_file *of,
 {
 	struct task_group *tg = css_tg(of_css(of));
 	u64 period = tg_get_cfs_period(tg);
-	u64 burst = tg_get_cfs_burst(tg);
+	u64 burst = tg->cfs_bandwidth.burst;
 	u64 quota;
 	int ret;
 
-- 
2.25.1