kern/59132: t_futex_ops:futex_wait_timeout_* sometimes fails on early wakeup

[campbell+netbsd%mumble.net@localhost]

>Number:         59132
>Category:       kern
>Synopsis:       t_futex_ops:futex_wait_timeout_* sometimes fails on early wakeup
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Mar 05 13:35:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The NetBSD Futexwakeupearly
>Environment:
>Description:
tc-start: 1741180577.73934, futex_wait_timeout_deadline
tc-se:*** Check failed: /home/riastradh/netbsd/current/src/tests/lib/libc/sys/t_futex_ops.c:1334: ts=98.529265778sec deadline=98.544610297sec
tc-end: 1741180579.62123, futex_wait_timeout_deadline, failed, 1 checks failed; see output for more details
tc-start: 1741180579.62211, futex_wait_timeout_deadline_rt
tc-end: 1741180581.51927, futex_wait_timeout_deadline_rt, passed
tc-start: 1741180581.52108, futex_wait_timeout_relative
tc-se:*** Check failed: /home/riastradh/netbsd/current/src/tests/lib/libc/sys/t_futex_ops.c:1334: ts=102.509214057sec deadline=102.522998637sec
tc-end: 1741180583.42052, futex_wait_timeout_relative, failed, 1 checks failed; see output for more details
tc-start: 1741180583.42136, futex_wait_timeout_relative_rt
tc-end: 1741180585.38947, futex_wait_timeout_relative_rt, passed

This is under qemu-system-x86_64 with nvmm on a NetBSD 10ish host.

So far I've only recorded seeing it with the monotonic clock, not the realtime clock (!), but I saw it in passing while testing other things and wasn't paying close attention so I can't rule out failures with the realtime clock too.
>How-To-Repeat:
1. boot NetBSD-current under qemu
2. cd /usr/tests/lib/libc/sys && atf-run t_futex_ops
>Fix:
Yes, please!