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Jakub reported that ASSERT_EQ(cpu, i) in so_incoming_cpu.c seems to
fire somewhat randomly.
# # RUN so_incoming_cpu.before_reuseport.test3 ...
# # so_incoming_cpu.c:191:test3:Expected cpu (32) == i (0)
# # test3: Test terminated by assertion
# # FAIL so_incoming_cpu.before_reuseport.test3
# not ok 3 so_incoming_cpu.before_reuseport.test3
When the test failed, not-yet-accepted CLOSE_WAIT sockets received
SYN with a "challenging" SEQ number, which was sent from an unexpected
CPU that did not create the receiver.
The test basically does:
1. for each cpu:
1-1. create a server
1-2. set SO_INCOMING_CPU
2. for each cpu:
2-1. set cpu affinity
2-2. create some clients
2-3. let clients connect() to the server on the same cpu
2-4. close() clients
3. for each server:
3-1. accept() all child sockets
3-2. check if all children have the same SO_INCOMING_CPU with the server
The root cause was the close() in 2-4. and net.ipv4.tcp_tw_reuse.
In a loop of 2., close() changed the client state to FIN_WAIT_2, and
the peer transitioned to CLOSE_WAIT.
In another loop of 2., connect() happened to select the same port of
the FIN_WAIT_2 socket, and it was reused as the default value of
net.ipv4.tcp_tw_reuse is 2.
As a result, the new client sent SYN to the CLOSE_WAIT socket from
a different CPU, and the receiver's sk_incoming_cpu was overwritten
with unexpected CPU ID.
Also, the SYN had a different SEQ number, so the CLOSE_WAIT socket
responded with Challenge ACK. The new client properly returned RST
and effectively killed the CLOSE_WAIT socket.
This way, all clients were created successfully, but the error was
detected later by 3-2., ASSERT_EQ(cpu, i).
To avoid the failure, let's make sure that (i) the number of clients
is less than the number of available ports and (ii) such reuse never
happens.
Fixes: 6df96146b2 ("selftest: Add test for SO_INCOMING_CPU.")
Reported-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Tested-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20240120031642.67014-1-kuniyu@amazon.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Linux kernel
============
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