Re: [PATCH] sched/fair: limit burst to zero when cfs bandwidth is toggled off

[Tianchen Ding]

On 2022/8/9 20:03, Zhao Wenhui wrote:
> When the quota value in CFS bandwidth is set to -1, that imples the
> cfs bandwidth is toggled off. So the burst feature is supposed to
> be disable as well.
>
> Currently, when quota is -1, burst will not be check, so that it can be
> set to almost arbitery value. Examples:
>          mkdir /sys/fs/cgroup/cpu/test
>          echo -1 > /sys/fs/cgroup/cpu/test/cpu.cfs_quota_us
>          echo 10000000000000000 > /sys/fs/cgroup/cpu/test/cpu.cfs_burst_us
>
> Moreover, after the burst modified by this way, quota can't be set
> to any value:
>          echo 100000 > cpu.cfs_quota_us
>          -bash: echo: write error: Invalid argument
>
> This patch can ensure the burst value being zero and unalterable,
> when quota is set to -1.
>
> Fixes: f4183717b370 ("sched/fair: Introduce the burstable CFS controller")
> Reported-by: Zhao Gongyi <zhaogongyi@xxxxxxxxxx>
> Signed-off-by: Zhao Wenhui <zhaowenhui8@xxxxxxxxxx>

Nice catch! Thanks for the fix.
Reviewed-by: Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx>