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([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e3eb8f305sm4424438f8f.3.2026.10.24.07.50.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 24 Oct 2026 07:50:53 -0700 (PDT) Message-ID: Date: Sat, 24 Oct 2026 15:50:51 +0100 X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net v2] tcp: reject devmem tx with fastopen and repair To: Mina Almasry Cc: Kaifeng Wang , netdev@vger.kernel.org, edumazet@google.com, ncardwell@google.com, kuniyu@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, willemb@google.com, kaiyuanz@google.com, sdf@fomichev.me, linux-kernel@vger.kernel.org References: <20261019174522.55644-1-kaifengw@google.com> <4d5e00b9-5081-4530-ade5-41570e4a5b2f@gmail.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/21/26 18:15, Mina Almasry wrote: > On Wed, Oct 21, 2026 at 8:17 AM Pavel Begunkov wrote: ...>>> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c >>> index 87ef6d5cbfeb..2792923f0748 100644 >>> --- a/net/ipv4/tcp.c >>> +++ b/net/ipv4/tcp.c >>> @@ -1169,14 +1169,18 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) >>> zc = MSG_SPLICE_PAGES; >>> } >>> >>> - if (!sockc_err && sockc.dmabuf_id && (zc != MSG_ZEROCOPY || !binding)) { >>> - err = -EINVAL; >>> + if (sockc.dmabuf_id && (zc != MSG_ZEROCOPY || !binding)) { >> >> I wonder why it does sockc_err checks like that for devmem, e.g. instead of >> failing earlier. Maybe Mina remembers? > > IIRC, Paolo caught an issue where we were subtely changing behavior. > Like if someone passes in a bad sockc flags, it's usually ignored, but > if we process the sockc_err before we need it for devmem we change > behavior for existing users that were passing bad sockc but not using > devmem. Got the idea, thanks. Sounds like this chunk can potentially change it in the same way, though I'd need to look up that thread with Paolo to be sure. -- Pavel Begunkov