Re: [PATCH] sched/core: fix incorrect parameter burst in cpu_max_write()

[Vincent Guittot]

On Wed, 24 Apr 2024 at 15:29, Cheng Yu <serein.chengyu@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
> Fixes: f4183717b370 ("sched/fair: Introduce the burstable CFS controller")
> Signed-off-by: Cheng Yu <serein.chengyu@xxxxxxxxxx>
> Signed-off-by: Zhang Qiao <zhangqiao22@xxxxxxxxxx>

Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Tested-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

> ---
>  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
>
>