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Date: Thu, 18 Jun 2026 16:49:43 -0400
Message-ID: <e384ef2f478093a70af11980d2d1cdeb@kernel.org>
From: Tamir Duberstein <tamird@kernel.org>
To: Emil Tsalapatis <emil@etsalapatis.com>
Cc: 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>,
 Kumar Kartikeya Dwivedi <memxor@gmail.com>,
 Song Liu <song@kernel.org>,
 Yonghong Song <yonghong.song@linux.dev>,
 Jiri Olsa <jolsa@kernel.org>,
 Shuah Khan <shuah@kernel.org>,
 Andrea Righi <arighi@nvidia.com>,
 Xu Kuohai <xukuohai@huawei.com>,
 Andrea Righi <andrea.righi@canonical.com>,
 bpf@vger.kernel.org,
 linux-kernel@vger.kernel.org,
 linux-kselftest@vger.kernel.org,
 Andrew Werner <awerner32@gmail.com>,
 Zvi Effron <zeffron@riotgames.com>,
 Andrii Nakryiko <andriin@fb.com>
Subject: Re: [PATCH bpf 2/6] libbpf: ringbuf: Prevent NULL callback crash
In-Reply-To: <DJAWPR7RA9VX.2LHJ0V3EVGR7S@etsalapatis.com>
References: <20260613-bpf-ringbuf-fixes-v1-0-e623481cb724@kernel.org>
 <20260613-bpf-ringbuf-fixes-v1-2-e623481cb724@kernel.org>
 <DJAWPR7RA9VX.2LHJ0V3EVGR7S@etsalapatis.com>
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On Tue, Jun 16, 2026 at 08:44:13PM -0400, Emil Tsalapatis wrote:
[...]
> Can we just prevent a ring from being added with a NULL sample_cb?
> What's the use for permitting it?

I kept NULL callbacks valid because I plan to add a caller-owned
iterator that does not use callbacks. Rejecting NULL during construction
would prevent callers from creating iterator-only rings.

> Even if we don't, rechecking the callbacks every single time we
> consume the ringbuf seems overkill.

Your `unlikely()` suggestion on patch 6 applies here too, so I used it
in v2.