Re: [RESEND PATCH bpf-next v6 8/8] selftests/bpf: Add tests for open-coded task and css iter

From: Chuyi Zhou
Date: Thu Oct 19 2023 - 20:30:37 EST


Hello,

在 2023/10/20 08:03, Alexei Starovoitov 写道:
On Tue, Oct 17, 2023 at 11:18 PM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:

+
+SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
+__failure __msg("css_task_iter is only allowed in bpf_lsm and bpf iter-s")
+int BPF_PROG(iter_css_task_for_each)
+{
+ u64 cg_id = bpf_get_current_cgroup_id();
+ struct cgroup *cgrp = bpf_cgroup_from_id(cg_id);
+ struct cgroup_subsys_state *css;
+ struct task_struct *task;
+
+ if (cgrp == NULL)
+ return 0;
+ css = &cgrp->self;
+
+ bpf_for_each(css_task, task, css, CSS_TASK_ITER_PROCS) {
+
+ }
+ bpf_cgroup_release(cgrp);
+ return 0;
+}

I think we should relax allowlist in patch 2 further.
Any sleepable is safe.
Allowlist is needed to avoid dead locking on css_set_lock.
Any lsm and any iter (even non-sleepable) and any sleepable
seems to be safe.

Then the above test would need s/fentry.s/fentry/ to stay relevant.

I would also add:

SEC("iter/cgroup")
int cgroup_id_printer(struct bpf_iter__cgroup *ctx)
{
struct seq_file *seq = ctx->meta->seq;
struct cgroup *cgrp = ctx->cgroup;

/* epilogue */
if (cgrp == NULL) ..

bpf_for_each(css_task, task, css, CSS_TASK_ITER_PROCS) {
BPF_SEQ_PRINTF(); // something about task
}

To demonstrate how new kfunc iter can be combined with cgroup iter and
it won't deadlock, though cgroup iter is not sleepable.


OK.

I've applied the current set. Pls send a follow up. Thanks


I would try to send a follow up patch next week.

Thank.