Re: [RFC PATCH net-next] tcp: Add net.ipv4.tcp_purge_receive_queue sysctl

[Leon Hwang]

On 26/2/26 09:43, Jakub Kicinski wrote:
> On Wed, 25 Feb 2026 15:46:33 +0800 Leon Hwang wrote:
>> Issue:
>> When a TCP socket in the CLOSE_WAIT state receives a RST packet, the
>> current implementation does not clear the socket's receive queue. This
>> causes SKBs in the queue to remain allocated until the socket is
>> explicitly closed by the application. As a consequence:
>>
>> 1. The page pool pages held by these SKBs are not released.
> 
> On what kernel version and driver are you observing this?

# uname -r
6.19.0-061900-generic

# ethtool -i eth0
driver: mlx5_core
version: 6.19.0-061900-generic
firmware-version: 26.43.2566 (MT_0000000531)

In addition, the Python scripts below reproduce that SKBs remain in the
receive queue.

Thanks,
Leon

---

server.py:

import socket
import time

HOST, PORT = "127.0.0.1", 9999

s = socket.socket()
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 8 * 1024)

s.bind((HOST, PORT))
s.listen(1)

conn, addr = s.accept()
print("accepted", addr)

time.sleep(1)

print("Read 1st:", conn.recv(1))

try:
    conn.send(b"A")
    print("sent 1 byte to client")
except Exception as e:
    print("send failed:", e)

time.sleep(1)

conn.settimeout(0.2)
try:
    b = conn.recv(1)
    print("recv(1) after RST:", b, "len=", len(b))
except Exception as e:
    print("recv(1) after RST raised:", repr(e))

print("Conn remains opening..")

try:
    print("Press Ctrl+C to stop...")
    while True:
        time.sleep(1)
except KeyboardInterrupt:
    print("\nProgram interrupted by user. Exiting.")

conn.close()
s.close()


client.py:

import socket
import time

HOST, PORT = "127.0.0.1", 9999

c = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
c.connect((HOST, PORT))

payload = b"x" * (4 * 1024)  # 4KiB
c.sendall(payload)
time.sleep(0.1)
c.close()

time.sleep(3)