kern/123363: page fault on ppp start if tun0 doesn't exist

[Justin Jereza]

>  To submitter: can you please obtain a backtrace of this panic on
>  your own system with something like:
>   kgdb /boot/kernel/kernel.symbols /path/to/vmcore.0
>  and issue the "bt" command?

Backtrace:

#0  doadump () at pcpu.h:195
#1  0xc075c1e7 in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:409
#2  0xc075c4ac in panic (fmt=Variable "fmt" is not available.
) at /usr/src/sys/kern/kern_shutdown.c:563
#3  0xc0a4efac in trap_fatal (frame=0xd68229e4, eva=392) at
/usr/src/sys/i386/i386/trap.c:899
#4  0xc0a4f210 in trap_pfault (frame=0xd68229e4, usermode=0, eva=392)
at /usr/src/sys/i386/i386/trap.c:812
#5  0xc0a4fbd9 in trap (frame=0xd68229e4) at /usr/src/sys/i386/i386/trap.c:490
#6  0xc0a3684b in calltrap () at /usr/src/sys/i386/i386/exception.s:139
#7  0xc074fd02 in _mtx_lock_sleep (m=0xc3014d08, tid=3276153360,
opts=0, file=0x0, line=0)
    at /usr/src/sys/kern/kern_mutex.c:335
#8  0xc048b3e1 in hfsc_class_destroy (cl=0xc5b16000) at
/usr/src/sys/contrib/altq/altq/altq_hfsc.c:595
#9  0xc048b65b in hfsc_remove_altq (a=0xc45aa8c0) at
/usr/src/sys/contrib/altq/altq/altq_hfsc.c:350
#10 0xc04904ba in altq_remove (a=0xc45aa8c0) at
/usr/src/sys/contrib/altq/altq/altq_subr.c:655
#11 0xc317f309 in ?? ()
#12 0xc45aa8c0 in ?? ()
#13 0xc0b7edc0 in M_DEVBUF ()
#14 0xc31948e8 in ?? ()
#15 0x01000000 in ?? ()
#16 0x00000000 in ?? ()
#17 0xc2ea88b0 in ?? ()
#18 0xd6822be4 in ?? ()
#19 0xc3184295 in ?? ()
#20 0x00000016 in ?? ()
#21 0x00000000 in ?? ()
#22 0xc3191864 in ?? ()
#23 0x00000c55 in ?? ()
#24 0xc36c68d8 in ?? ()
#25 0x00000006 in ?? ()
#26 0xc36c6908 in ?? ()
#27 0xc3462210 in ?? ()
#28 0xc0ae10d5 in ?? ()
#29 0x00000119 in ?? ()
#30 0xd6822ae8 in ?? ()
#31 0xc0a64955 in VOP_UNLOCK_APV (vop=0x16, a=0x0) at vnode_if.c:1676
Previous frame inner to this frame (corrupt stack?)