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Tue, 27 May 2025 17:23:25 -0700 (PDT) Received: from ezingerman-mba ([2620:10d:c090:500::7:461c]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-311e9b636a4sm19982a91.19.2025.05.27.17.23.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 May 2025 17:23:25 -0700 (PDT) From: Eduard Zingerman To: Kumar Kartikeya Dwivedi Cc: bpf@vger.kernel.org, Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Emil Tsalapatis , Barret Rhoden , Matt Bobrowski , kkd@meta.com, kernel-team@meta.com Subject: Re: [PATCH bpf-next v2 01/11] bpf: Introduce BPF standard streams In-Reply-To: (Kumar Kartikeya Dwivedi's message of "Wed, 28 May 2025 01:55:20 +0200") References: <20250524011849.681425-1-memxor@gmail.com> <20250524011849.681425-2-memxor@gmail.com> Date: Tue, 27 May 2025 17:23:23 -0700 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Kumar Kartikeya Dwivedi writes: [...] >> > diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c >> > new file mode 100644 >> > index 000000000000..b9e6f7a43b1b >> > --- /dev/null >> > +++ b/kernel/bpf/stream.c >> >> [...] >> >> > +int bpf_stream_stage_commit(struct bpf_stream_stage *ss, struct bpf_prog *prog, >> > + enum bpf_stream_id stream_id) >> > +{ >> > + struct llist_node *list, *head, *tail; >> > + struct bpf_stream *stream; >> > + int ret; >> > + >> > + stream = bpf_stream_get(stream_id, prog->aux); >> > + if (!stream) >> > + return -EINVAL; >> > + >> > + ret = bpf_stream_consume_capacity(stream, ss->len); >> > + if (ret) >> > + return ret; >> > + >> > + list = llist_del_all(&ss->log); >> > + head = list; >> > + >> > + if (!list) >> > + return 0; >> > + while (llist_next(list)) { >> > + tail = llist_next(list); >> > + list = tail; >> > + } >> > + llist_add_batch(head, tail, &stream->log); >> >> If `llist_next(list) == NULL` at entry `tail` is never assigned? > > The assumption is llist_del_all being non-NULL means llist_next is > going to return a non-NULL value at least once. > Does that address your concern? Sorry, maybe I don't understand something. Suppose that at entry ss->log is a list with a single element: ss->log -> 0xAA: { .next = NULL; ... payload ... } then: - list == 0xAA; - llist_next(list) == 0x0; - loop body never executes. What do I miss? >> > + return 0; >> > +} [...]