On Mon, Jun 27, 2022 at 9:14 PM Yonghong Song [off-list ref] wrote:

quoted

+static int __cgroup_iter_seq_show(struct seq_file *seq,
+                               struct cgroup_subsys_state *css, int in_stop)
+{
+     struct cgroup_iter_priv *p = seq->private;
+     struct bpf_iter__cgroup ctx;
+     struct bpf_iter_meta meta;
+     struct bpf_prog *prog;
+     int ret = 0;
+
+     /* cgroup is dead, skip this element */
+     if (css && cgroup_is_dead(css->cgroup))
+             return 0;
+
+     ctx.meta = &meta;
+     ctx.cgroup = css ? css->cgroup : NULL;
+     meta.seq = seq;
+     prog = bpf_iter_get_info(&meta, in_stop);
+     if (prog)
+             ret = bpf_iter_run_prog(prog, &ctx);

Do we need to do anything special to ensure bpf program gets
up-to-date stat from ctx.cgroup?

Let's leave that to be handled by bpf programs. The kfunc rstat_flush
can be called to sync stats, if using rstat.

quoted

+
+     /* if prog returns > 0, terminate after this element. */
+     if (ret != 0)
+             p->terminate = true;
+
+     return 0;
+}
+

[...]