Subject: Re: [PATCH net-next v2 2/2] selftests: net: add ECMP rehash test

From: Jakub Kicinski <[email-masked]>
Date: Wed, 8 Apr 2026 09:38:08 -0700

On Wed,  8 Apr 2026 00:05:14 -0700 Neil Spring wrote:
> Add ecmp_rehash.sh to exercise TCP ECMP path re-selection on
> retransmission timeout.  Three tests cover client SYN rehash, server
> SYN/ACK rehash, and midstream RTO rehash of an established connection
> over a two-path ECMP topology with one leg blocked by tc.
> 
> The SYN test retries 26 times, so has a false negative probability
> of ~(1/2)^25 ≈ 3e-8.

I think this is failing in netdev CI:

TAP version 13
1..1
# timeout set to 3600
# selftests: net: ecmp_rehash.sh
# 30.31 [+30.31] TEST: ECMP RTO rehash: establish with blocked paths                 [FAIL]
# 30.31 [+0.00] SYNs did not appear on both paths (rehash not working)
# 30.32 [+0.01] 2026/04/07 23:36:18 socat[18706] W exiting on signal 15
# 33.44 [+3.12] 2026/04/07 23:36:21 socat[21325] E read(7, 0x560db4041000, 8192): Connection reset by peer
# 33.45 [+0.01] TEST: ECMP SYN/ACK rehash: blocked return path                      [ OK ]
# 33.45 [+0.01] 2026/04/07 23:36:21 socat[21137] W exiting on signal 15
# 34.76 [+1.31] 51TEST: ECMP midstream rehash: block active path                      [FAIL]
# 99.81 [+65.04] data transfer failed after blocking veth0a
# 99.82 [+0.01] 2026/04/07 23:37:27 socat[21345] W exiting on signal 15
not ok 1 selftests: net: ecmp_rehash.sh # exit=1

Also please start a new thread when you post v3.