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[108.212.132.20]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7d7eadcb757sm11429957a34.15.2026.03.23.23.04.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Mar 2026 23:04:27 -0700 (PDT) From: Wesley Atwell To: netdev@vger.kernel.org Cc: linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, davem@davemloft.net, edumazet@google.com, ncardwell@google.com, kuniyu@google.com, dsahern@kernel.org, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, shuah@kernel.org, gmbnomis@gmail.com, Wesley Atwell Subject: [PATCH net-next v2 3/3] selftests: packetdrill: cover scaled rwnd quantization slack Date: Tue, 24 Mar 2026 00:04:10 -0600 Message-ID: <20260324060410.1137199-4-atwellwea@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260324060410.1137199-1-atwellwea@gmail.com> References: <20260324060410.1137199-1-atwellwea@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add a packetdrill reproducer for the free_space-limited scaled no-shrink quantization case. Grow rcv_ssthresh with in-order data, then queue tiny OOO skbs so receive memory drives raw free_space just below rcv_ssthresh without advancing rcv_nxt. The final ACK reaches the case where raw free_space sits just above 84 scaled units while rcv_ssthresh stays slightly larger. Old code rounds that final free_space value up and advertises 85. With the fix, the ACK stays at 84. This gives fail-before/pass-after coverage for the actual raw free_space bug rather than the separate rcv_ssthresh-limited ALIGN-up behavior. Signed-off-by: Wesley Atwell --- v2: - replace the old rcv_ssthresh-limited sequence with an OOO-memory reproducer for the raw free_space case - drop the follow-on ACK transition and keep the final free_space failure case that proves the bug - drop the IPv4-only restriction after verifying the test passes for ipv4, ipv6, and ipv4-mapped-ipv6 - reword the in-file comments to describe the observed behavior without referring to a removed path as "buggy" .../packetdrill/tcp_rcv_quantization_credit.pkt | 62 ++++++++++++++++++= ++++ 1 file changed, 62 insertions(+) create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcv_quantiz= ation_credit.pkt diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_quantization_c= redit.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_quantization_cr= edit.pkt new file mode 100644 index 000000000000..bb4f63772326 --- /dev/null +++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_quantization_credit.p= kt @@ -0,0 +1,62 @@ +// SPDX-License-Identifier: GPL-2.0 + +--mss=3D1000 + +`./defaults.sh +sysctl -q net.ipv4.tcp_moderate_rcvbuf=3D0 +sysctl -q net.ipv4.tcp_shrink_window=3D0 +sysctl -q net.ipv4.tcp_rmem=3D"4096 131072 $((32*1024*1024))"` + +// Exercise the scaled no-shrink path when raw backed free_space, not +// rcv_ssthresh, limits the post-ACK window in __tcp_select_window(). +// +// Grow rcv_ssthresh with in-order data, then queue tiny OOO skbs so recei= ve +// memory drops raw free_space to just over 84 scaled units while the curr= ent +// rcv_ssthresh stays slightly larger. The final OOO ACK should keep the +// sender-visible window at 84 rather than reopening it to 85. + +0 socket(..., SOCK_STREAM, IPPROTO_TCP) =3D 3 + +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) =3D 0 + +0 bind(3, ..., ...) =3D 0 + +0 listen(3, 1) =3D 0 + + +0 < S 0:0(0) win 32792 + +0 > S. 0:0(0) ack 1 + +0 < . 1:1(0) ack 1 win 257 + + +0 accept(3, ..., ...) =3D 4 + + +0 < P. 1:10001(10000) ack 1 win 257 + * > . 1:1(0) ack 10001 + + +0 < P. 10001:11024(1023) ack 1 win 257 + * > . 1:1(0) ack 11024 + + +0 < P. 12024:12025(1) ack 1 win 257 + * > . 1:1(0) ack 11024 + + +0 < P. 13024:13025(1) ack 1 win 257 + * > . 1:1(0) ack 11024 + + +0 < P. 14024:14025(1) ack 1 win 257 + * > . 1:1(0) ack 11024 + + +0 < P. 15024:15025(1) ack 1 win 257 + * > . 1:1(0) ack 11024 + + +0 < P. 16024:16025(1) ack 1 win 257 + * > . 1:1(0) ack 11024 + + +0 < P. 17024:17025(1) ack 1 win 257 + * > . 1:1(0) ack 11024 + + +0 < P. 18024:18025(1) ack 1 win 257 + * > . 1:1(0) ack 11024 + + +0 < P. 19024:19025(1) ack 1 win 257 + * > . 1:1(0) ack 11024 + +// The last tiny OOO skb pushes raw free_space just below rcv_ssthresh +// without crossing the next lower scaled unit. + +0 < P. 20024:20025(1) ack 1 win 257 + * > . 1:1(0) ack 11024 win 84 + +0 %{ assert (tcpi_rcv_wnd >> 10) =3D=3D 84, tcpi_rcv_wnd }% --=20 2.43.0