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

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Message-ID: <92e8f98e-466d-45be-aa0a-35e02419a5c0@bytedance.com>
Date:   Fri, 20 Oct 2023 08:30:03 +0800
From:   Chuyi Zhou <zhouchuyi@...edance.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH bpf-next v6 8/8] selftests/bpf: Add tests for
 open-coded task and css iter

Hello,

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