kern/38782: Panic at uvm_swap_markbad when starting Xorg

[adam.hoka%gmail.com@localhost]

>Number:         38782
>Category:       kern
>Synopsis:       Panic at uvm_swap_markbad when starting Xorg
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed May 28 19:10:00 +0000 2008
>Originator:     Adam Hoka
>Release:        4.99.63 i386
>Organization:
>Environment:
NetBSD grimnismal.regius.local 4.99.63 NetBSD 4.99.63 (GENERIC) #0: Mon May 26 
00:34:32 CEST 2008  
replaced%grimnismal.regius.local@localhost:/tnf/build/obj/sys/arch/i386/compile/GENERIC
 i386

>Description:
When running Xorg (from pkgsrc) for the first time works OK, but often, when 
shutting it down and starting again the screen ends up staying black.

As the keyboard seemed still responsive, I blindly typed 'sync', so I have a 
crash dump.

The panic message was this:

uvm_fault(0xcc3ebd08, 0, 1) -> 0xe
kernel: supervisor trap page fault, code=0
Stopped in pid 15917.1 (Xorg) at        netbsd:uvm_swap_markbad+0x30:   movl    
0x24(%eax),%eax
?
db{0}> syncing disks... 1 done

And the backtrace was:

#0  0xc0630f10 in cpu_reboot ()
#1  0xc01e755e in db_sync_cmd ()
#2  0xc01e6e03 in db_command ()
#3  0xc01e6687 in db_command_loop ()
#4  0xc01eaaf0 in db_trap ()
#5  0xc062c525 in kdb_trap ()
#6  0xc063641b in trap ()
#7  0xc010cdc8 in calltrap ()
#8  0xc04d7237 in uvm_swap_markbad ()
#9  0xc04bd847 in uao_get ()
#10 0xc04cfa17 in uobj_wirepages ()
#11 0xc0578cc1 in sys_shmget ()
#12 0xc0635e2a in syscall ()
#13 0xc0100514 in syscall1 ()

Similar freezes happen during a normal X11 session too sometimes, but I don't 
know if they are related.
>How-To-Repeat:
login
startx
ctrl-alt-backspace
startx

repeat till freeze
>Fix: