port-evbarm/60269: System hangs NetBSD/evbarm(aarch64) 11.0_RC4

["oshima-ya%yagoto-urayama.jp@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60269
>Category:       port-evbarm
>Synopsis:       System hangs NetBSD/evbarm(aarch64) 11.0_RC4
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-evbarm-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat May 16 04:25:00 +0000 2026
>Originator:     Yasushi Oshima
>Release:        11.0_RC4
>Organization:
>Environment:
NetBSD nable 11.0_RC4 NetBSD 11.0_RC4 (GENERIC64) #0: Thu May 14 09:46:21 JST 2026  oshima@sudachi:/export/netbsd-11/20260514/obj/evbarm64/sys/arch/evbarm/compile/GENERIC64 evbarm
>Description:
After upgrading NetBSD/evbarm (aarch64)to 11.0_RC4 on my RasPi4, the system frequently hangs. This often occurs while building several applications from pkgsrc. As a result, a response of shell or any commands suddenly stops, and SSH sessions from the network are disconnected.

When the system hangs, it is possible to start ddb from the console using Ctrl-Alt-ESC. I found the process states by ps revealed several processes stuck on rwlock.
 (see https://x.com/oshimyja/status/2054966172375032207/photo/1)

For example, this frequently happens when building www/firefox. It can also occur during daily cron jobs. 
No such issues were observed in 11.0_RC2.
I don't know whether other architectures are affected.
At least, it doesn't happen on my amd64 11.0_RC4 environment.

This system is booted from a USB stick, and no crash dumps have been obtained.
>How-To-Repeat:
On NetBSD/evbarm(GENERIC64) 11.0_RC4, 
Build some pkgsrcs

>Fix:
None, but I check the source change history and found the following changes, then backout these and rebuild libc and related components, no further hangs have occurred so far:

https://mail-index.netbsd.org/source-changes/2026/05/07/msg161941.html

I think some of these changes is causing the issue.