From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-00082601.pphosted.com (mx0b-00082601.pphosted.com [67.231.153.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 99725372045 for ; Fri, 22 May 2026 21:57:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=67.231.153.30 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779487059; cv=none; b=a4aKaemsVtGpnxh07H9hdpn3ylcwhU56fcZTlf57MPTnvryCjBA2YCJO2/Xlpcerkk+PNNPk8I/kJ5bnwM0F2Yon4ntP22aPptII2APFVtMR8kLOsVsvbuvv57A8XPtaieLOZcfVCb/i2WKXFXIXNtyRzf5yBbCgKlon4a/ZxJE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779487059; c=relaxed/simple; bh=juil23xToy9CQ8hrlNcwOM0/VzXLtL5uef1zMIkRi/c=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=jSnUARac+TAikyzV/k6Gt/JXAc/cjND7VzGTpWdpm/ytcZtTJ8KjPJchks1G0BklTQ2H5mS+MRqA4c+AahNOM5VH9WPRxz+WSNimacMUOva7qqqPKIyRGbAcOmTWBdXahxdRX+jQbjqI4ntWc2igYxHA209Itl9BUqWB/00HPBs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=meta.com; spf=pass smtp.mailfrom=meta.com; dkim=pass (2048-bit key) header.d=meta.com header.i=@meta.com header.b=FTEQ8CZr; arc=none smtp.client-ip=67.231.153.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=meta.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=meta.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=meta.com header.i=@meta.com header.b="FTEQ8CZr" Received: from pps.filterd (m0528005.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 64MKNvU33209767 for ; Fri, 22 May 2026 14:57:36 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=meta.com; h=cc :content-transfer-encoding:date:from:message-id:mime-version :subject:to; s=s2048-2025-q2; bh=WsnLCyDet0IE96jpLaIya/EHaqC1Px4 MftDg7/35Ods=; b=FTEQ8CZr/b9qCpAOtn3KwkTAeF94NaXvfPHTHdk4nP4opY6 uqItIZtIISQTeClTnHMbdq7DyaoyjIET/0YBZdEslniMy3fWE1hjl3/4gVWBepCM cd1xRZikNg/vAEoGd6SH3C1GEQCQkSCpEH7MsdK8iGBxSOcXnY6YCT3Y7BC4KdcS 51OhpY9Z/knNWIJ0gxpcNLtx3cgjBPs/qviJdMg6w/buqQt76NvVaTZJh7KZ2gSm VYUEMP9Iseec+DYzdewXFZnAb6dh3riPbUTzlQqZSKm39yLMpT4UuMVaIaGbFCYL HKAv3Zp+1TnCrizUmowANNfNCQ4u+imONKNbwbQ== Received: from mail-oo1-f71.google.com (mail-oo1-f71.google.com [209.85.161.71]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 4eaag16txd-1 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NOT) for ; Fri, 22 May 2026 14:57:36 -0700 (PDT) Received: by mail-oo1-f71.google.com with SMTP id 006d021491bc7-69d7fee2b39so961196eaf.1 for ; Fri, 22 May 2026 14:57:36 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779487056; x=1780091856; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=WsnLCyDet0IE96jpLaIya/EHaqC1Px4MftDg7/35Ods=; b=pUfBqaZEvycIPqBA2AsRXzlFA0BBmwndISh3gufjd2voks6y94Z9Lww7KaJFPR7Gpa wN6HpIqgKO6W693nLVsWK3a51AWFwF+huIFXE/wl56FWHml7R1meUnJlOH5a0FJp2GuJ inAKBsLVo1lBxAcBdgsAr8ZEzha5EekzgTu4Q8mK1O/2bn5wkKBaYtZAWOixbZtmdZBD FiMrUSq8G+X4n1UOPO/yrHn3g9J1G0cvZL7Mfe7oVqwjeYS35TrLyh0N2XfpT9uEsk9D ki/tvlkHSLUN4iQaajmv7f4Q1i9vuxbiYhC4g17rANu2MmMWkUygqZc/osThYoJsLr7t HoCw== X-Forwarded-Encrypted: i=1; AFNElJ8qX9RUMlNAPTMSKQJaCUkH+oLpP27XHgys1L/W79kYGxzt0m4qU2+jSAUWHSW7aPPwKrU=@vger.kernel.org X-Gm-Message-State: AOJu0Yzh2nQajprxgJLsfEJmOvrspF9AwcqGnx9EN7cLAiUIHukEU3n+ bWX4M9IYaDW6kl5CnwBAf1/+Hoc52kw0OIq8ah+JXU5PXcW1OQL4XKY81I55ICG/8c8LRIIhD8c 0HBkZyC/tvvwhh/fTmde/ozbhvkTm/DJCmmGvMcIqTVa4OyvdW00= X-Gm-Gg: Acq92OGGzjSkwi32lfpuYAs01ZqVGZ83LRR/Q9TG/IugRVZX6BPHxhyhCXEDdCTU2aT ihdHSyrgwEIJnRIkjpybmLc2MCAfI+NBwhJNaMLe0TeG5k4SrXEiCSUrw517s5tWHlXNcwWiykf VH1A7lfCkNUXoJQUt3sQ+uJFGp+X97gYsEdxKM68hOihdZ6PThDC+nOhU4gsy4nckES4f6kB7jj WwU6r2F/A6WePYQYq0DMHmukrSTwE3VRd99xQSV17dNwYp0iR9uoi3WgNn/VbMrJOrx3GD/wSbJ BNsWpFHSKKpmAADx0QIRICRBq7bz3x59IiG7/jLSKGQrb5blbtMXv8eOzX+VLxvSio2ouKPcEZZ nqRAhF1i9ZA== X-Received: by 2002:a05:6820:8c6:b0:696:8325:f7eb with SMTP id 006d021491bc7-69d7ecd0c9amr2823576eaf.45.1779487055615; Fri, 22 May 2026 14:57:35 -0700 (PDT) X-Received: by 2002:a05:6820:8c6:b0:696:8325:f7eb with SMTP id 006d021491bc7-69d7ecd0c9amr2823549eaf.45.1779487054977; Fri, 22 May 2026 14:57:34 -0700 (PDT) Received: from localhost ([2a03:2880:12ff:7::]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-69d83a4db17sm1485917eaf.9.2026.05.22.14.57.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 22 May 2026 14:57:34 -0700 (PDT) From: Neil Spring To: netdev@vger.kernel.org Cc: edumazet@google.com, ncardwell@google.com, kuniyu@google.com, davem@davemloft.net, kuba@kernel.org, dsahern@kernel.org, pabeni@redhat.com, horms@kernel.org, shuah@kernel.org, linux-kselftest@vger.kernel.org, ntspring@meta.com, bpf@vger.kernel.org, martin.lau@linux.dev, daniel@iogearbox.net Subject: [PATCH net-next v8 0/2] tcp: rehash onto different local ECMP path on retransmit timeout Date: Fri, 22 May 2026 14:57:31 -0700 Message-ID: <20260522215733.929238-1-ntspring@meta.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Authority-Analysis: v=2.4 cv=Vr4Txe2n c=1 sm=1 tr=0 ts=6a10d150 cx=c_pps a=V4L7fE8DliODT/OoDI2WOg==:117 a=xqWC_Br6kY4A:10 a=NGcC8JguVDcA:10 a=f7IdgyKtn90A:10 a=VkNPw1HP01LnGYTKEx00:22 a=7x6HtfJdh03M6CCDgxCd:22 a=jCddH8ec0KUNCymVuxII:22 a=VwQbUJbxAAAA:8 a=VabnemYjAAAA:8 a=Tm2zCBzp3FQG0QxiXacA:9 a=WZGXeFmKUf7gPmL3hEjn:22 a=gKebqoRLp9LExxC7YDUY:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTIyMDIxOCBTYWx0ZWRfX1p0XrlZO7Uxn 4GtL/0n9Pf4PvcH0G1WexnWhSWTw9D8qviIQix643/TI4TrsC8VpZ4FfSxzAXGOh7vA4GefMYqE 6sdDp09DV9uIHcevXqyv0YJQS/8svUkoUiWNhfqVrGn5l9df42QuVu2cNX/cNQO5U4gg6Zp43l6 IkUzKVP7UMYbIoSdbE8jOju77MiJrevdKH7wPW/gIIxtHhHx6BNVRQ8ef7jqVcg3Rd6Enm4xMW2 AoBnhkHUlui+vlpLR106wkBIk1CSkxqOgoKOOESQGhhTzoTlNWgPlA5Xo6dLZ04faBpQUf1zitz 80tSmrsBas/Bd/3LgMiRr7lAzbqdMtNSYNymOMFhVUwnm+QOZjfuGsxpMlNhNqSMiJaBg7DdVfO HDmgSPrn820y+J8jsErNVKldt0OlIbEWzVrQkHWjzav3bMzGIb5tV10RP5zICcthL3dPHKdV7f9 JY08oPg0ye9YCDJlQfQ== X-Proofpoint-GUID: bf8DnSe89PfiRrtirLQKLXflpY_5BmpK X-Proofpoint-ORIG-GUID: bf8DnSe89PfiRrtirLQKLXflpY_5BmpK X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-22_06,2026-05-18_01,2025-10-01_01 Currently sk_rethink_txhash() re-rolls the socket's txhash on RTO, PLB, and spurious-retransmission events, but the new hash is not propagated into the IPv6 ECMP path selection logic. The cached route is reused and fib6_select_path() is never re-invoked, so so the connection uses the same local ECMP decision. This series adds the two missing pieces: 1. __sk_dst_reset() alongside sk_rethink_txhash() so the cached dst is invalidated and the next transmit triggers a fresh route lookup. 2. fl6->mp_hash set from sk_txhash before each route lookup so fib6_select_path() picks a path based on the (potentially re-rolled) hash. This is conditioned on fib_multipath_hash_policy == 0 (L3) because policies 1-3 compute a deterministic hash from the flow keys which must not be overridden. Patch 1 is the kernel change; patch 2 adds selftests covering SYN rehash, SYN/ACK rehash, midstream RTO rehash, midstream ACK rehash (spurious retransmission), PLB rehash, a policy 1 negative test, a flowlabel leak regression test, two dst rebuild consistency tests (normal and syncookie) verifying that natural route invalidation does not cause unintended path changes, and a syncookie server path consistency test verifying that the SYN-ACK and post-cookie ACKs use the same ECMP nexthop. I'd like guidance on whether to use the ISN as txhash when using syncookies; it keeps the SYN-ACK and subsequent data path consistent, but one could argue that this consistency doesn't matter because no reordering is possible. Changes since v7: https://lore.kernel.org/netdev/20260520064310.4154268-1-ntspring@meta.com/ Patch 1: - Remove #if IS_ENABLED(CONFIG_IPV6) guards around __sk_dst_reset() in tcp_plb.c and tcp_timer.c (Eric Dumazet) - Guard mp_hash in inet6_csk_route_socket() on sk_protocol == IPPROTO_TCP instead of txhash != 0, since non-TCP callers like L2TP set sk_txhash in __ip6_datagram_connect() and should retain flow-key-based ECMP - Use the syncookie (ISN) as txhash for both the SYN-ACK route lookup and cookie_v6_check() socket creation, so the server's ECMP selection is consistent across the stateless SYN-ACK and the subsequent full socket. Move cookie_init_sequence() before route_req() in tcp_conn_request() so the SYN-ACK dst is computed with the cookie-derived txhash; derive txhash from snt_isn in cookie_tcp_reqsk_init() to match Patch 2: - Invalidate dst via dummy route add/del instead of route replace to avoid a transient single-nexthop state during multipath replacement - Add syncookie server path consistency test verifying the SYN-ACK and post-cookie ACKs use the same ECMP path - Strengthen policy 1 negative test to wait for multiple rehash attempts and verify SYNs landed on exactly one interface Changes since v6: https://lore.kernel.org/netdev/20260517174522.2232057-1-ntspring@meta.com/ - Guard mp_hash assignment so that non-TCP callers of inet6_csk_route_socket() fall through to rt6_multipath_hash() (superseded in v8 by sk_protocol == IPPROTO_TCP guard) - Initialize txhash in bpf_sk_assign_tcp_reqsk() to avoid reading uninitialized slab memory in inet6_csk_route_req() - Check post-rebuild busywait return status to avoid silent false pass Changes since v5: https://lore.kernel.org/netdev/20260513204048.2721843-1-ntspring@meta.com/ - Improve selftest reliability: suppress __dst_negative_advice() via tcp_retries1=255 in dst rebuild tests so a real RTO cannot trigger an unintended rehash; add internal retry to midstream and ACK rehash tests to tolerate probabilistic ECMP path selection; fix midstream baseline capture to account for packets that bypass tc filters during the prio qdisc's TCQ_F_CAN_BYPASS window - Increase ECMP_REBUILD_ROUNDS default to 10 for reliable regression detection with 2-way ECMP; replace sleep with busywait - Use tcp_allowed_congestion_control instead of changing the host's default congestion control for PLB test - Use (txhash >> 1) ?: 1 to guarantee non-zero mp_hash, since zero falls back to rt6_multipath_hash() Changes since v4: https://lore.kernel.org/netdev/20260507171319.1259115-1-ntspring@meta.com/ - Condition fl6->mp_hash on fib_multipath_hash_policy == 0 to preserve deterministic hash policies 1-3 (e.g., symmetric 5-tuple for policy 1) - Set fl6->mp_hash in tcp_v6_connect() and cookie_v6_check() for initial route lookup consistency; move sk_set_txhash() earlier (Jakub Kicinski) - Add policy 1 negative test; improve sysctl save/restore - Add flowlabel leak test confirming mp_hash does not alter the on-wire IPv6 flow label - Add dst rebuild consistency tests (normal and syncookie) verifying that route table changes do not cause unintended ECMP path changes Changes since v3: https://lore.kernel.org/netdev/20260505193824.2791642-1-ntspring@meta.com/ - Use __sk_dst_reset() instead of sk_dst_reset() since the socket lock is held in all three call sites (Eric Dumazet) - Guard __sk_dst_reset() with sk->sk_family == AF_INET6 since IPv4 ECMP does not use sk_txhash for path selection - Guard __sk_dst_reset() in tcp_plb_check_rehash() with the return value of sk_rethink_txhash() - Move tcp_rsk(req)->txhash initialization before route_req() in tcp_conn_request() to avoid reading uninitialized memory - Add CONFIG_TCP_CONG_DCTCP=m to selftests/net/config for PLB test - Skip PLB test gracefully if DCTCP is not available - Save and restore original congestion control algorithm in PLB test - Default get_netstat_counter() to 0 when counter is not found - Skip all tests if tcp_syn_linear_timeouts is not available - Replace bash/pipe data sources with socat OPEN:/dev/zero for cleaner process cleanup - Fix shellcheck warnings Changes since v2: https://lore.kernel.org/netdev/20260408070514.1840227-1-ntspring@meta.com/ - Retitle "ECMP" to "local ECMP" to distinguish from remote ECMP (Neal Cardwell) - Add fl6->mp_hash propagation in inet6_sk_rebuild_header() (af_inet6.c), covering the dst rebuild path used on established sockets - Remove incorrect ir_iif update from tcp_check_req() in tcp_minisocks.c; the SYN/ACK rehash is already handled by tcp_rtx_synack() re-rolling txhash which feeds into inet6_csk_route_req()'s mp_hash (Eric Dumazet) - Add ACK rehash and PLB rehash selftests - Improve selftest reliability Changes since v1: https://lore.kernel.org/netdev/20260408002802.2448424-1-ntspring@meta.com/ - Use tcp_rsk(req)->txhash instead of jhash_1word(req->num_retrans, ...) for ECMP path selection in inet6_csk_route_req(), making the request socket path consistent with the established socket path (Eric Dumazet) - Add comments explaining the >> 1 shift for 31-bit mp_hash range - Use socat -u (unidirectional) in selftest to avoid SIGPIPE race - Increase tcp_syn_retries and tcp_syn_linear_timeouts to 25 for better rehash coverage Neil Spring (2): tcp: rehash onto different local ECMP path on retransmit timeout selftests: net: add local ECMP rehash test net/core/filter.c | 1 + net/ipv4/tcp_input.c | 6 +- net/ipv4/tcp_plb.c | 5 +- net/ipv4/tcp_timer.c | 2 + net/ipv6/af_inet6.c | 3 + net/ipv6/inet6_connection_sock.c | 7 + net/ipv6/syncookies.c | 4 + net/ipv6/tcp_ipv6.c | 13 +- tools/testing/selftests/net/Makefile | 1 + tools/testing/selftests/net/config | 1 + tools/testing/selftests/net/ecmp_rehash.sh | 952 +++++++++++++++++++++ 11 files changed, 990 insertions(+), 5 deletions(-) create mode 100755 tools/testing/selftests/net/ecmp_rehash.sh -- 2.53.0-Meta