Re: [PATCH] sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The patch fails to initialize the new `idle` field in `struct scx_cgroup_init_args` in the sub-scheduler paths, causing it to implicitly default to false and lose the correct idle state.
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--- Patch [1]: [PATCH] sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args ---
commit 6b122f2bce26c31e18660129955114867f5a36b0
Author: Tao Cui <[email protected]>

sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args

This commit adds the idle state to scx_cgroup_init_args and initializes it
in scx_tg_online() and scx_cgroup_init(). This ensures that cgroups already
configured as idle before the scheduler is loaded are correctly presented as
idle to the BPF scheduler.

> diff --git a/kernel/sched/ext/internal.h b/kernel/sched/ext/internal.h
> index 53e136a47924d..aa149a9c29f7b 100644
> --- a/kernel/sched/ext/internal.h
> +++ b/kernel/sched/ext/internal.h
> @@ -259,6 +259,9 @@ struct scx_cgroup_init_args {
>  	u64			bw_period_us;
>  	u64			bw_quota_us;
>  	u64			bw_burst_us;
> +
> +	/* whether the cgroup is configured idle via cpu.idle */
> +	bool			idle;
>  };

[Severity: Medium]
When adding this new field, did we miss updating the struct initialization in
the sub-scheduler paths?

Looking at kernel/sched/ext/sub.c, both scx_cgroup_claim_subtree() and
scx_cgroup_return_subtree() initialize the struct but omit the new field:

kernel/sched/ext/sub.c:scx_cgroup_claim_subtree() {
    ...
		struct scx_cgroup_init_args args = {
			.weight = tg->scx.weight,
			.bw_period_us = tg->scx.bw_period_us,
			.bw_quota_us = tg->scx.bw_quota_us,
			.bw_burst_us = tg->scx.bw_burst_us,
		};
    ...
}

The exact same pattern also exists in scx_cgroup_return_subtree().

Without explicitly setting the idle field in these paths, wouldn't it
implicitly default to false, causing cgroups to incorrectly lose their idle
state when a sub-scheduler is enabled or disabled?

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Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=1