[PATCH 6.1 277/473] sched/core: Fix incorrect initialization of the burst parameter in cpu_max_write()

Greg Kroah-Hartman
2024-06-06T14:16:33Z

From: Cheng Yu <serein.chengyu@huawei.com>

[ Upstream commit 49217ea147df7647cb89161b805c797487783fc0 ]

In the cgroup v2 CPU subsystem, assuming we have a
cgroup named 'test', and 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 find 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, get the burst value directly from tg->cfs_bandwidth.burst.

Fixes: f4183717b370 ("sched/fair: Introduce the burstable CFS controller")
Reported-by: Qixin Liao <liaoqixin@huawei.com>
Signed-off-by: Cheng Yu <serein.chengyu@huawei.com>
Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240424132438.514720-1-serein.chengyu@huawei.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 18a4f8f28a25f..d71234729edb4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11117,7 +11117,7 @@ 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;

--
2.43.0