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From: Roman Gushchin <roman.gushchin@linux.dev>
To: Matt Bobrowski <mattbobrowski@google.com>
Cc: bpf@vger.kernel.org,  Alexei Starovoitov <ast@kernel.org>,  Daniel
 Borkmann <daniel@iogearbox.net>,  Andrii Nakryiko <andrii@kernel.org>,
  Martin KaFai Lau <martin.lau@linux.dev>,  Eduard Zingerman
 <eddyz87@gmail.com>,  Song Liu <song@kernel.org>,  Yonghong Song
 <yonghong.song@linux.dev>,  ohn Fastabend <john.fastabend@gmail.com>,  KP
 Singh <kpsingh@kernel.org>,  Stanislav Fomichev <sdf@fomichev.me>,  Jiri
 Olsa <jolsa@kernel.org>
Subject: Re: [PATCH bpf-next] bpf: Revert "bpf: drop KF_ACQUIRE flag on BPF
 kfunc bpf_get_root_mem_cgroup()"
In-Reply-To: <20260121090001.240166-1-mattbobrowski@google.com> (Matt
	Bobrowski's message of "Wed, 21 Jan 2026 09:00:01 +0000")
References: <20260121090001.240166-1-mattbobrowski@google.com>
Date: Wed, 21 Jan 2026 10:47:57 -0800
Message-ID: <87o6mm7qg2.fsf@linux.dev>
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Matt Bobrowski <mattbobrowski@google.com> writes:

> This reverts commit e463b6de9da1 ("bpf: drop KF_ACQUIRE flag on BPF
> kfunc bpf_get_root_mem_cgroup()").
>
> The original commit removed the KF_ACQUIRE flag from
> bpf_get_root_mem_cgroup() under the assumption that it resulted in
> simplified usage. This stemmed from the fact that
> bpf_get_root_mem_cgroup() inherently returns a reference to an object
> which technically isn't reference counted, therefore there is no
> strong requirement to call a matching bpf_put_mem_cgroup() on the
> returned reference.
>
> Although technically correct, as per the arguments in the thread [0],
> dropping the KF_ACQUIRE flag and losing reference tracking semantics
> negatively impacted the usability of bpf_get_root_mem_cgroup() in
> practice.
>
> [0] https://lore.kernel.org/bpf/878qdx6yut.fsf@linux.dev/
>
> Link: https://lore.kernel.org/bpf/CAADnVQ+6d1Lj4dteAv8u62d7kj3Ze5io6bqM0xeQd-UPk9ZgJQ@mail.gmail.com/
> Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>

Acked-by: Roman Gushchin <roman.gushchin@linux.dev>

Thanks, Matt!