port-arm/57102: vcmbox0 thread using 100% CPU

[cryintothebluesky%gmail.com@localhost]

>Number:         57102
>Category:       port-arm
>Synopsis:       vcmbox0 thread using 100% CPU
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-arm-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Dec 10 16:05:00 +0000 2022
>Originator:     Sad Clouds
>Release:        9.99.108
>Organization:
>Environment:
NetBSD rp4 9.99.108 NetBSD 9.99.108 (GENERIC64) #0: Fri Dec  9 13:52:51 GMT 2022
>Description:
The issue occurred on Raspberry Pi 4, used as NFS server. Initiated a large copy from Linux NFS client to NetBSD NFS server. Some time later, vcmbox0 thread was consuming 100% CPU and the following message was logged before I rebooted the system

Dec 10 15:01:13 rp4 /netbsd: [ 721.2070326] vcmbox0: workqueue busy: updates stopped

Running envstat on command line blocked indefinitely.

Reboot was the only way to resolve the issue. Looks like there may be a bug that results in infinite loop.
>How-To-Repeat:
Not sure, after reboot, subsequent NFS usage did not reproduce the issue.
>Fix: