Add a packetdrill reproducer for the scaled no-shrink quantization case. The sequence leaves slightly more than 84 scaled units of backed credit after one skb is drained. The buggy ALIGN() path rounds that up and exposes a fresh extra unit, so the wire-visible window becomes 85.
Then queue a tiny OOO skb so the next ACK re-runs the no-shrink path after a small receive-memory change without advancing rcv_nxt. With the fix in place, both ACKs keep the sender-visible window at 84. This provides fail-before/pass-after coverage for both the immediate quantization bug and the follow-on ACK transition that reuses the stored window state. Signed-off-by: Wesley Atwell <[email protected]> --- .../packetdrill/tcp_rcv_quantization_credit.pkt | 45 ++++++++++++++++++++++ 1 file changed, 45 insertions(+) create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcv_quantization_credit.pkt diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_quantization_credit.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_quantization_credit.pkt new file mode 100644 index 0000000000000000000000000000000000000000..8ea96281b601f2d161cfd84967cad91cedb03151 --- /dev/null +++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_quantization_credit.pkt @@ -0,0 +1,45 @@ +// SPDX-License-Identifier: GPL-2.0 + +--ip_version=ipv4 +--mss=1000 + +`./defaults.sh +sysctl -q net.ipv4.tcp_moderate_rcvbuf=0 +sysctl -q net.ipv4.tcp_shrink_window=0 +sysctl -q net.ipv4.tcp_rmem="4096 131072 $((32*1024*1024))"` + +// Exercise the scaled no-shrink path in __tcp_select_window(). +// The sequence below leaves slightly more than 84 scaled units of backed +// credit after one skb is drained. The buggy ALIGN() path rounds that up and +// exposes a fresh extra unit; the fixed path keeps the sender-visible window +// at 84. Then queue a tiny OOO skb so the next ACK re-runs the no-shrink +// path after a small receive-memory change without advancing rcv_nxt. + +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 + +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 + +0 bind(3, ..., ...) = 0 + +0 listen(3, 1) = 0 + + +0 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7> + +0 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 10> + +0 < . 1:1(0) ack 1 win 257 + + +0 accept(3, ..., ...) = 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 + +// Free one skb, then force an outbound packet so the current advertised +// window is observable both on the wire and via TCP_INFO. + +0 read(4, ..., 10000) = 10000 + +0 write(4, ..., 1) = 1 + * > P. 1:2(1) ack 11024 win 84 + +0 %{ assert (tcpi_rcv_wnd >> 10) == 84, tcpi_rcv_wnd }% + +// Queue a tiny OOO skb. This should not create fresh sender-visible credit +// on the next ACK after the first post-drain window update. + +0 < P. 12024:12025(1) ack 2 win 257 + * > . 2:2(0) ack 11024 win 84 + +0 %{ assert (tcpi_rcv_wnd >> 10) == 84, tcpi_rcv_wnd }% -- 2.43.0
