On Mon, Aug 17, 2026 at 05:24:49PM -0700, Ziyang Men wrote:
> +++ b/kernel/cgroup/bpf_cpu.c
Probably not the best file name. bpf_cgroup.c or maybe just put it in
cgroup.c?
> +/**
> + * bpf_css_to_task_group - Cast a CPU controller css to its task group
> + * @css: CPU controller css
> + *
> + * Must be called under RCU.
> + * A C cast does not give the verifier a task_group pointer. This kfunc
> + * preserves the task_group and per-CPU types needed to read cfs_rq.
The fact that this is used for per-CPU types now probably won't age well if
this grows more usages in the future.
> + *
> + * Return: The task group, or NULL if @css belongs to another controller.
> + */
> +__bpf_kfunc struct task_group *
> +bpf_css_to_task_group(struct cgroup_subsys_state *css)
> +{
> + if (css->ss != &cpu_cgrp_subsys)
unlikely()?
> + return NULL;
> +
> + /* task_group embeds css at offset zero. */
> + return (struct task_group *)css;
container_of()?
> +/**
> + * bpf_css_flush_rstat - Flush a cgroup subsystem's rstat data
> + * @css: cgroup subsystem state to flush
> + */
> +__bpf_kfunc void bpf_css_flush_rstat(struct cgroup_subsys_state *css)
> +{
> + css_rstat_flush(css);
> +}
Why is this necessary? Isn't css_rstat_flush() already exposed as a kfunc?
> +/**
> + * bpf_cgroup_base_stat - Read a cgroup's base statistics
> + * @cgrp: cgroup to read from
> + * @out: zero-initialized output in nanoseconds
> + *
> + * CPU time is adjusted as for cpu.stat.
> + */
> +__bpf_kfunc void bpf_cgroup_base_stat(struct cgroup *cgrp,
> + struct cgroup_base_stat *out)
> +{
> + if (cgroup_parent(cgrp)) {
> + __css_rstat_lock(&cgrp->self, -1);
> + *out = cgrp->bstat;
> + cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime,
> + &out->cputime.utime, &out->cputime.stime);
> + __css_rstat_unlock(&cgrp->self, -1);
> + } else {
> + root_cgroup_cputime(out);
> + }
> +}
> +
> +__bpf_kfunc_end_defs();
> +
> +BTF_KFUNCS_START(bpf_rstat_common_kfunc_ids)
> +BTF_ID_FLAGS(func, bpf_css_flush_rstat, KF_SLEEPABLE)
> +BTF_ID_FLAGS(func, bpf_cgroup_base_stat, KF_SLEEPABLE)
Why are these SLEEPABLE?
Thanks.
--
tejun
