kern/57345: Automated test kernel/kqueue/t_empty fails intermittently on an amd64 machine

[jspath55%gmail.com@localhost]

>Number:         57345
>Category:       kern
>Synopsis:       Automated test kernel/kqueue/t_empty fails intermittently on an amd64 machine
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Apr 12 17:30:01 +0000 2023
>Originator:     Jim Spath
>Release:        10.0_BETA
>Organization:
>Environment:
NetBSD hi.me 10.0_BETA NetBSD 10.0_BETA (GENERIC) #0: Sun Feb 12 12:39:37 UTC 2023  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64 x86_64 AMD 686-class NetBSD
>Description:
With several full automated test framework passes done, I found some tests that fail (or succeed) intermittently. When this test fails for me, the output is:

tps-count: 1
tp-start: 1680663191.765848, kernel/kqueue/t_empty, 1
tc-start: 1680663191.765881, sock_tcp
tc-end: 1680663191.777728, sock_tcp, failed, /usr/src/tests/kernel/kqueue/t_empty.c:167: (readsock = accept(readsock, (struct sockaddr *)&sin, &slen)) != -1 not met
tp-end: 1680663191.778046, kernel/kqueue/t_empty
info: time.end, Wed Apr 5 02:53:11 UTC 2023

I next ran loops of 10, 20 and 30 runs, finding failures about half the time (but not getting a pass first, then a fail, and then another pass).

With 30 repetitions, one result showed 19 passes (and 11 failures):
$ grep passed  ~/tests.t_empty_x30.txt | wc -l
      19

Then I set up frequent runs driven by a cron job, for just over 24 hours. Pass/fail summary:
$ grep tc-end t*log | awk '{print $1, $3, $4, $5}' | sort | uniq -c
 812 tc-end: sock_tcp, failed, /usr/src/tests/kernel/kqueue/t_empty.c:167:
1018 tc-end: sock_tcp, passed 

I also rebooted the machine, shut down optional applications but still see failures.
>How-To-Repeat:
The test run command is:

cd /usr/tests
atf-run kernel/kqueue/t_empty 
>Fix:
Unknown root cause.