linux-kernel - Re: [PATCH] sched/fair: Fix burst unit mismatch error for cgroup v2 cfsb.

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Message-ID: <CALJBpEcTPYFUmkkSKKS5WkFG0ekDHB-ZUeJacTGXZVOjP7yCzg@mail.gmail.com>
Date:   Wed, 30 Aug 2023 17:19:14 +0800
From:   牛若飞 <nrf233@...il.com>
To:     peterz@...radead.org
Cc:     coonwel@...il.com, qiang.zhang1211@...il.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Fix burst unit mismatch error for cgroup v2 cfsb.

Cc:  linux-kernel@...r.kernel.org


NiuRuofei <nrf233@...il.com> 于2023年8月9日周三 14:27写道：
>
> The burstable CFS controller is introduced:
> Link: https://lore.kernel.org/lkml/20210316044931.39733-2-changhuaixin@linux.alibaba.com/
>
> The original patch directly used the 'cpu.max' interface file, and it handles the unit conversion
> when cpu_period_quota_parse() function called(something like this, *burstp *= NSEC_PER_USEC;), it works fine.
>
> However, in the official version,  the single "cpu.max" file was split into 'cpu.max' and 'cpu.max.burst' interface files,
> and we don't parse 'burst' in cpu_period_quota_parse() function anymore. Instead, we call tg_get_cfs_burst() to get burst value,
> which return burst_time in microseconds. This could result in a unit mismatch bug.
>
> We can easily reproduce this bug using the following steps:
>         bash:/sys/fs/cgroup/mycgroup$ echo 25000 | sudo tee cpu.max.burst
>         25000
>         bash:/sys/fs/cgroup/mycgroup$ echo 50000 100000 | sudo tee cpu.max
>         50000 100000
>         bash:/sys/fs/cgroup/mycgroup$ cat cpu.max.burst
>         25
>
> Signed-off-by: NiuRuofei <nrf233@...il.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 c52c2eba7c73..e635598486a9 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -11380,7 +11380,7 @@ 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_get_cfs_burst(tg) * NSEC_PER_USEC;
>         u64 quota;
>         int ret;
>
> --
> 2.30.1 (Apple Git-130)
>