system lock-up using 8.99.1

[Paul Goyette <paul%whooppee.com@localhost>]

With a system built from sources dated 2017-07-15 at 09:06:30 UTC....

I had a backup running in one session, using 'dump -X ...' (to use an 
internal fs(4) snapshot of the file system), and in another session I 
was doing a whole bunch of umount(8)'s of null-mounted file systems 
(running "$PATH/sandbox umount").

With no warning, the system completely hung.  No keyboard or mouse 
activity, and other background processes like xosview stopped updating. 
Unable to get a core dump or even a stack trace, since I could not get 
into ddb.  (Even if I could, my keyboard is attached via xhci/usb3, so 
doesn't work for ddb.)

I have no idea if this is reproducible, but I thought it might be useful 
for others to be aware.


+------------------+--------------------------+----------------------------+
| Paul Goyette     | PGP Key fingerprint:     | E-mail addresses:          |
| (Retired)        | FA29 0E3B 35AF E8AE 6651 | paul at whooppee dot com   |
| Kernel Developer | 0786 F758 55DE 53BA 7731 | pgoyette at netbsd dot org |
+------------------+--------------------------+----------------------------+