linux-kernel - Re: [PATCH bpf-next v2 2/6] bpf: Introduce css

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Message-ID: <88825625-283a-d521-3e7e-058784455577@bytedance.com>
Date:   Wed, 13 Sep 2023 12:56:55 +0800
From:   Chuyi Zhou <zhouchuyi@...edance.com>
To:     Martin KaFai Lau <martin.lau@...ux.dev>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...nel.org, tj@...nel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 2/6] bpf: Introduce css_task open-coded
 iterator kfuncs

Hello Martin.

在 2023/9/13 03:57, Martin KaFai Lau 写道:
> On 9/12/23 12:01 AM, Chuyi Zhou wrote:
>> +__bpf_kfunc int bpf_iter_css_task_new(struct bpf_iter_css_task *it,
>> +        struct cgroup_subsys_state *css, unsigned int flags)
>> +{
>> +    struct bpf_iter_css_task_kern *kit = (void *)it;
>> +
>> +    BUILD_BUG_ON(sizeof(struct bpf_iter_css_task_kern) != 
>> sizeof(struct bpf_iter_css_task));
>> +    BUILD_BUG_ON(__alignof__(struct bpf_iter_css_task_kern) !=
>> +                    __alignof__(struct bpf_iter_css_task));
>> +
>> +    switch (flags) {
>> +    case CSS_TASK_ITER_PROCS | CSS_TASK_ITER_THREADED:
>> +    case CSS_TASK_ITER_PROCS:
>> +    case 0:
>> +        break;
>> +    default:
>> +        return -EINVAL;
>> +    }
>> +
>> +    kit->css_it = kzalloc(sizeof(struct css_task_iter), GFP_KERNEL);
>> +    if (!kit->css_it)
>> +        return -ENOMEM;
>> +    css_task_iter_start(css, flags, kit->css_it);
>> +    return 0;
>> +}
>> +
> 
>> +static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
>> +{
>> +    enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
>> +
>> +    switch (prog_type) {
>> +    case BPF_PROG_TYPE_LSM:
> 
> This will allow the non-sleepable lsm prog to call 
> bpf_iter_css_task_new. The above kzalloc(GFP_KERNEL) in 
> bpf_iter_css_task_new should trigger a lockdep error in the lsm selftest 
> in patch 6.

Thanks for your test. I missed the dmesg error since I did not set 
CONFIG_LOCKDEP.

I think here we can use kzalloc(GFP_ATOMIC) to eliminate this error if 
we want to use this iter in non-sleepable lsm prog. I just tested, it 
works well.

> 
>> +        return true;
>> +    case BPF_TRACE_ITER:
>> +        return env->prog->aux->sleepable;
>> +    default:
>> +        return false;
>> +    }
>> +}
>