linux-kernel - Re: [PATCH v2 02/23] bpf: initial support for attaching struct ops to cgroups

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Message-ID: <87cy65e9nw.fsf@linux.dev>
Date: Wed, 29 Oct 2025 13:26:59 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Song Liu <song@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
  linux-kernel@...r.kernel.org,  Alexei Starovoitov <ast@...nel.org>,
  Suren Baghdasaryan <surenb@...gle.com>,  Michal Hocko
 <mhocko@...nel.org>,  Shakeel Butt <shakeel.butt@...ux.dev>,  Johannes
 Weiner <hannes@...xchg.org>,  Andrii Nakryiko <andrii@...nel.org>,  JP
 Kobryn <inwardvessel@...il.com>,  linux-mm@...ck.org,
  cgroups@...r.kernel.org,  bpf@...r.kernel.org,  Martin KaFai Lau
 <martin.lau@...nel.org>,  Kumar Kartikeya Dwivedi <memxor@...il.com>,
  Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v2 02/23] bpf: initial support for attaching struct ops
 to cgroups

Song Liu <song@...nel.org> writes:

> On Mon, Oct 27, 2025 at 4:17 PM Roman Gushchin <roman.gushchin@...ux.dev> wrote:
> [...]
>>  struct bpf_struct_ops_value {
>>         struct bpf_struct_ops_common_value common;
>> @@ -1359,6 +1360,18 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
>>         }
>>         bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_map_lops, NULL,
>>                       attr->link_create.attach_type);
>> +#ifdef CONFIG_CGROUPS
>> +       if (attr->link_create.cgroup.relative_fd) {
>> +               struct cgroup *cgrp;
>> +
>> +               cgrp = cgroup_get_from_fd(attr->link_create.cgroup.relative_fd);
>
> We should use "target_fd" here, not relative_fd.

Ok, thanks!

>
> Also, 0 is a valid fd, so we cannot use target_fd == 0 to attach to
> global memcg.

Yep, switching to using root_memcg's fd instead.

Thanks!