Re: [PATCH bpf-next v2] bpf: Do not allocate percpu memory at init stage

[Yonghong Song <yonghong.song@linux.dev>]

On 11/10/23 12:32 PM, Alexei Starovoitov wrote:
> On Fri, Nov 10, 2023 at 9:23 AM Yonghong Song <yonghong.song@linux.dev> wrote:
>> +                               if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {
>> +                                       if (!bpf_global_percpu_ma_set) {
>> +                                               mutex_lock(&bpf_verifier_lock);
>> +                                               if (!bpf_global_percpu_ma_set) {
>> +                                                       err = bpf_mem_alloc_init(&bpf_global_percpu_ma, 0, true);
>> +                                                       if (!err)
>> +                                                               bpf_global_percpu_ma_set = true;
>> +                                               }
>> +                                               mutex_unlock(&bpf_verifier_lock);
> I feel we're taking unnecessary risk here by reusing the mutex.
> bpf_obj_new kfunc is a privileged operation and the verifier lock
> is not held in such scenario, so it won't deadlock,

That is true. deadlock situation won't happen.

> but let's just add another mutex to protect percpu_ma init.
> Much easier to reason about.

Okay. will do.