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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fc7d468b3sm40811125e9.13.2026.09.18.02.51.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Sep 2026 02:51:43 -0700 (PDT) Date: Fri, 18 Sep 2026 10:51:42 +0100 From: David Laight To: Quanye Yang via B4 Relay Cc: quanyeyang@proton.me, Eric Dumazet , Neal Cardwell , Kuniyuki Iwashima , "David S. Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , "Matthieu Baerts (NGI0)" , Geliang Tang , Mat Martineau , Jiayuan Chen , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next v4 1/2] tcp: annotate lockless access to sk->sk_err Message-ID: <20260918105142.3dc675eb@pumpkin> In-Reply-To: <20260917-mptcp-sk-err-net-v4-1-1f04f52f2561@proton.me> References: <20260917-mptcp-sk-err-net-v4-0-1f04f52f2561@proton.me> <20260917-mptcp-sk-err-net-v4-1-1f04f52f2561@proton.me> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 17 Sep 2026 06:41:22 -0700 Quanye Yang via B4 Relay wrote: > From: Quanye Yang > > BUG: KCSAN: data-race in do_recvmmsg / mptcp_recvmsg > > read-write (marked) to 0xffff8880134d391c of 4 bytes by task 2619 on cpu 1: > instrument_atomic_read_write include/linux/instrumented.h:113 [inline] > sock_error include/net/sock.h:2565 [inline] > do_recvmmsg+0x50c/0x580 net/socket.c:3049 > __sys_recvmmsg net/socket.c:3144 [inline] > __do_sys_recvmmsg net/socket.c:3167 [inline] > __se_sys_recvmmsg net/socket.c:3160 [inline] > __x64_sys_recvmmsg+0x161/0x180 net/socket.c:3160 > x64_sys_call+0x19c7/0x1ca0 arch/x86/include/generated/asm/syscalls_64.h:300 > do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] > do_syscall_64+0xde/0x3d0 arch/x86/entry/syscall_64.c:84 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > read to 0xffff8880134d391c of 4 bytes by task 2620 on cpu 0: > tcp_recv_should_stop include/net/tcp.h:3086 [inline] > mptcp_recvmsg+0x54d/0xd50 net/mptcp/protocol.c:2466 > inet_recvmsg+0x204/0x210 net/ipv4/af_inet.c:894 > sock_recvmsg_nosec net/socket.c:1151 [inline] > sock_recvmsg+0x11a/0x140 net/socket.c:1173 > ____sys_recvmsg+0x14b/0x3c0 net/socket.c:2933 > ___sys_recvmsg+0x116/0x160 net/socket.c:2975 > __sys_recvmsg net/socket.c:3008 [inline] > __do_sys_recvmsg net/socket.c:3014 [inline] > __se_sys_recvmsg net/socket.c:3011 [inline] > __x64_sys_recvmsg+0xeb/0x160 net/socket.c:3011 > x64_sys_call+0x1319/0x1ca0 arch/x86/include/generated/asm/syscalls_64.h:48 > do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] > do_syscall_64+0xde/0x3d0 arch/x86/entry/syscall_64.c:84 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > value changed: 0x0000006b -> 0x00000000 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 UID: 0 PID: 2620 Comm: syz.2.33 Not tainted 7.2.0-g39d4f32c5d53 #76 PREEMPT(full) > Hardware name: QEMU Ubuntu 26.04 PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1ubuntu1 04/01/2014 > > do_recvmmsg() and getsockopt(SO_ERROR) call sock_error() without the > socket lock. sock_error() clears sk_err with xchg(), which races with > unmarked loads of the same field. > > KCSAN reported the unmarked peek in tcp_recv_should_stop(). The same > lockless writer races with the other plain sk_err reads on the TCP > send, recv and splice paths. > > Annotate those peeks with READ_ONCE(). No extra ordering is needed: > the value is only used to decide whether I/O should stop. This does > not consume sk_err; the check-then-sock_error() TOCTOU on the no-data > paths is a separate issue. MPTCP peeks are handled in the next patch. Don't they need annotating with data_race() ? David