[PATCH net-next 0/2] tcp: rehash onto different ECMP path on retransmit timeout

[Neil Spring <ntspring@meta.com>]

I configured an ECMP route across two local interfaces, expecting
autoflowlabel to adapt when one of those interfaces is blocked in
reaching the destination.  However, it did not.  This affected SYN,
SYN/ACK, and established traffic.

I was able to make this work as I expected it to by calling
sk_dst_reset() at times when txhash was updated, and propagating
sk_txhash into fl6->mp_hash so fib6_select_path() uses the socket's
current hash for ECMP selection.

I expected autoflowlabel to apply to local ECMP routes, and think
it should, but am open to feedback if this isn't the right way to
do it.

Patch 1 has the kernel changes; patch 2 adds a selftest exercising
SYN, SYN/ACK, and established connection rehash over a two-path
ECMP topology.  The selftest retries a SYN 26 times, so has a tiny
(~3e-8) probability of false failure if repeatedly unlucky with ECMP
path selection.

Neil Spring (2):
  tcp: rehash onto different ECMP path on retransmit timeout
  selftests: net: add ECMP rehash test

 net/ipv4/tcp_input.c                       |   4 +-
 net/ipv4/tcp_minisocks.c                   |   9 +
 net/ipv4/tcp_plb.c                         |   1 +
 net/ipv4/tcp_timer.c                       |   1 +
 net/ipv6/inet6_connection_sock.c           |   8 +
 tools/testing/selftests/net/Makefile       |   1 +
 tools/testing/selftests/net/ecmp_rehash.sh | 354 +++++++++++++++++++++
 7 files changed, 377 insertions(+), 1 deletion(-)
 create mode 100755 tools/testing/selftests/net/ecmp_rehash.sh

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2.52.0