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

[Honglei Wang]

On 2023/8/30 17:19, 牛若飞 wrote:
> Cc:  linux-kernel@xxxxxxxxxxxxxxx
>
>
> NiuRuofei <nrf233@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxx/
> >
> > 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@xxxxxxxxx>
> > ---
> >   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)
Seems we had a similar fix for this one from Kailun here:
https://lkml.org/lkml/2021/9/10/782