kern/53072: netbsd-8 regression: startx (nv driver) crashes system

[rcbixler%nyx.net@localhost]

>Number:         53072
>Category:       kern
>Synopsis:       netbsd-8 regression: startx (nv driver) crashes system
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Mar 04 14:40:01 +0000 2018
>Originator:     Roy Bixler
>Release:        netbsd-8
>Organization:
>Environment:
NetBSD laptop.bix.org 8.0_BETA NetBSD 8.0_BETA (GENERIC.201802271630Z) i386
>Description:
System is an old Dell laptop (Precision M70) with an NVidia graphics card.  It doesn't work with the Nouveau DRM (problem reported in bug #50804), but it works with the old X server nv driver.  When I upgraded to the kernel above, I found that "startx" crashes the system.  It reboots and leaves a crash dump:

_KERNEL_OPT_NARCNET(0,104,c011e2a5,8,c0fff385,0,104,c0f73de5,dabefc5c,dabefc40) a
t 0
__kernel_end(104,0,c0f73de5,dabefc5c,c2b6ed40,6,dabefce4,dabefc50,c0947c9a,c0f73
de5) at dabefc5c
vpanic(c0f73de5,dabefc5c,dabefcd8,c0120935,c0f73de5,dabefce4,dabefce4,1,dabed2c0
,13246) at vpanic+0x131
snprintf(c0f73de5,dabefce4,dabefce4,1,dabed2c0,13246,8,0,0,0) at snprintf
trap_tss() at trap_tss
--- trap via task gate ---
_KERNEL_OPT_BEEP_ONHALT_COUNT+0x2:

The Xorg.0.log file from the crashed "startx" is:

[   123.004] (**) |-->Input Device "Keyboard0"
[   123.004] (==) Not automatically adding devices
[   123.004] (==) Not automatically enabling devices
[   123.004] (==) Not automatically adding GPU devices
[   123.004] (==) Max clients allowed: 256, resource mask: 0x1fffff
[   123.005] (**) FontPath set to:
        /usr/X11R7/lib/X11/fonts/misc/,
        /usr/X11R7/lib/X11/fonts/TTF/,
        /usr/X11R7/lib/X11/fonts/Type1/,
        /usr/X11R7/lib/X11/fonts/75dpi/,
        /usr/X11R7/lib/X11/fonts/100dpi/,
        /usr/X11R7/lib/X11/fonts/misc/,
        /usr/X11R7/lib/X11/fonts/TTF/,
        /usr/X11R7/lib/X11/fonts/Type1/,
        /usr/X11R7/lib/X11/fonts/75dpi/,
        /usr/X11R7/lib/X11/fonts/100dpi/
[   123.005] (**) ModulePath set to "/usr/X11R7/lib/modules"
[   123.005] Number of created screens does not match number of detected devices.
  Configuration failed.
[   123.006] (EE) Server terminated with error (2). Closing log fil

When I revert to the previous build:

NetBSD laptop.bix.org 8.0_BETA NetBSD 8.0_BETA (GENERIC.201802262040Z) i386

the X works and the system is usable again.  I suspect that this change "[pullup-8 #593] please pullup pmap & pool(9) fixes for netbsd-8" is the issue.
>How-To-Repeat:
Boot up a NetBSD-8 build on or after 201802271630Z with nouveau driver disabled and run "startx" as a normal user.
>Fix:
Revert to a prior NetBSD-8 build, such as the previous one on 201802262040Z.