locking assertion failed with 6.99.28

[Darren Reed <darrenr%netbsd.org@localhost>]

After doing a halt on a SunBlade 2500 that was running 6.99.28 I saw the 
messages below on the console.

Darren

May 23 03:56:49 syncing disks... done
unmounting file systems...
unmounting done
syncing disks... done
cd0: detached
brgphy1: detached
sd1: detached
sd0: detached
atapibus0: detached
cas0: detached
Reader / writer lock error: rw_vector_enter: assertion failed: !cpu_intr_p()

lock address : 0x0000000001ce2cf8
current cpu  :                  1
current lwp  : 0x0000000107691900
owner/count  : 000000000000000000 flags    : 000000000000000000

Skipping crash dump on recursive panic
panic: lock error
cpu1: Begin traceback...
cpu1: End traceback...
cpu0: shutting down
cpu1: rebooting