I've replicated the problem on another box.  A few more observations:

1) Can also occur if /tmp resides on root partition (or anyplace else?)
2) Can also occur doing 'bzip2 -d' on large files
3) Still occurs even if more swap space assigned (e.g. 160Mb for 16Mb
machine);
    swap usage (as shown by 'swapctl -lk') never goes beyond 24Mb
4) Doesn't occur when using a custom kernel (GENERIC_TINY, with addition of
    XSERVER, MFS, UCONSOLE and some PCI network drivers - and omission
    of I686_CPU

In cases 1 thru 3, the console message is:
---
kernel: page fault trap, code=0
Stopped at      sw1+0x15:       movl     %eax,     0x4(%edx)
db> reboot
---
So my impression is that it's something in the GENERIC kernel - or perhaps
in I686-specific code.

Any more suggestions??

G.

> -----Original Message-----
> From:	Jenkins, Graham K [IBM GSA] [SMTP:Graham.K.Jenkins@team.telstra.com]
> Sent:	Saturday, 28 July 2001 10:12 pm
> To:	'port-i386@netbsd.org '
> Subject:	NetBSD 1.5.1 GENERIC Kernel Crash with /tmp on mfs
> 
> Guys, I've had a number of kernel crashes whilst trying to build
> a new kernel on a 486 with 16Mb memory, with /tmp on a memory filesystem
> in swap space.  Happens about 40 minutes after restarting the 'make'. 
> Unmounting /tmp seemed to solve the problem.
> 
> I don't think its a memory fault - I've seeen a similar thing on another
> machine running NetBSD 1.5
> 
> Anybody else seen this?  And anybody have a fix?
> 
> G.