netdev - [PATCH v3 2/2] net/tcp: add packetdrill test for FIN-WAIT-1 zero-window fix

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Message-ID: <20251027141542.3746029-3-wokezhong@tencent.com>
Date: Mon, 27 Oct 2025 22:15:42 +0800
From: HaiYang Zhong <wokezhong@...il.com>
To: kuniyu@...gle.com
Cc: davem@...emloft.net,
	dsahern@...nel.org,
	edumazet@...gle.com,
	horms@...nel.org,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	ncardwell@...gle.com,
	netdev@...r.kernel.org,
	pabeni@...hat.com,
	wokezhong@...il.com,
	wokezhong@...cent.com
Subject: [PATCH v3 2/2] net/tcp: add packetdrill test for FIN-WAIT-1 zero-window fix

Move the packetdrill test to the packetdrill directory and shorten
the test duration.

In the previous packetdrill test script, the long duration was due to
presenting the entire zero-window probe backoff process. The test has
been modified to only observe the first few packets to shorten the test
time while still effectively verifying the fix.

- Moved test to tools/testing/selftests/net/packetdrill/
- Reduced test duration from 360+ seconds to under 4 seconds

Signed-off-by: HaiYang Zhong <wokezhong@...cent.com>
---
 .../packetdrill/tcp_fin_wait1_zero_window.pkt | 34 +++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_fin_wait1_zero_window.pkt

diff --git a/tools/testing/selftests/net/packetdrill/tcp_fin_wait1_zero_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_fin_wait1_zero_window.pkt
new file mode 100644
index 000000000000..854ede56e7dd
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_fin_wait1_zero_window.pkt
@@ -0,0 +1,34 @@
+// Test for permanent FIN-WAIT-1 state with continuous zero-window advertisements
+// Author: HaiYang Zhong <wokezhong@...cent.com>
+
+
+0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+0.000 bind(3, ..., ...) = 0
+0.000 listen(3, 1) = 0
+
+0.100 < S 0:0(0) win 65535 <mss 1460>
+0.100 > S. 0:0(0) ack 1 <mss 1460>
+0.100 < . 1:1(0) ack 1 win 65535
+0.100 accept(3, ..., ...) = 4
+
+// Send data to fill receive window
+0.200 write(4, ..., 5) = 5
+0.200 > P. 1:6(5) ack 1
+
+// Advertise zero-window
+0.200 < . 1:1(0) ack 6 win 0
+
+// Application closes connection, sends FIN (but blocked by zero window)
+0.200 close(4) = 0
+
+//Send zero-window probe packet
++0.200 > . 5:5(0) ack 1
++0.400 > . 5:5(0) ack 1
++0.800 > . 5:5(0) ack 1
+
++1.000 < . 1:1(0) ack 6 win 0
+
+// Without fix: This probe won't match - timer was reset, probe will be sent 2.600s after the previous probe
+// With fix: This probe matches - exponential backoff continues (1.600s after previous probe)
++0.600~+0.700 > . 5:5(0) ack 1
-- 
2.43.7