kern/52120: dump -X can panic the system

[Manuel.Bouyer%lip6.fr@localhost]

>Number:         52120
>Category:       kern
>Synopsis:       dump -X can panic the system
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Mar 28 11:45:00 +0000 2017
>Originator:     Manuel Bouyer
>Release:        NetBSD 6.1_STABLE
>Organization:
>Environment:
System: NetBSD armandeche.soc.lip6.fr 6.1_STABLE NetBSD 6.1_STABLE (ADMIN_DOM0) #9: Thu Mar 23 15:53:15 MET 2017  bouyer%disco.soc.lip6.fr@localhost:/home/bouyer/src-6/src/sys/arch/amd64/compile/ADMIN_DOM0 amd64
Architecture: x86_64
Machine: amd64
>Description:
	while running backups with dump -X (via amanda-client), I got this
	panic:
login: panic: itrunc3
cpu0: Begin traceback...
printf_nolog() at netbsd:printf_nolog
ffs_truncate() at netbsd:ffs_truncate+0x1082
ufs_inactive() at netbsd:ufs_inactive+0x2df
VOP_INACTIVE() at netbsd:VOP_INACTIVE+0x54
vrelel() at netbsd:vrelel+0x246
fss_ioctl() at netbsd:fss_ioctl+0x214
fss_close() at netbsd:fss_close+0x9f
spec_close() at netbsd:spec_close+0x110
VOP_CLOSE() at netbsd:VOP_CLOSE+0x51
vn_close() at netbsd:vn_close+0x37
closef() at netbsd:closef+0x54
fd_free() at netbsd:fd_free+0x11d
exit1() at netbsd:exit1+0x11a
sys_exit() at netbsd:sys_exit+0x3e
syscall() at netbsd:syscall+0xc4
cpu0: End traceback...

	It's not the first time I run into panics because of dump -X on the
	netbsd-6 branch, because I periodically forget to rebuild amamda
	without amanda-dump-snap.

>How-To-Repeat:
	run dump -X on a netbsd-6 host. It's not 100% reproductible,
	it's probably dependant on other filesystem activity.
>Fix:
	workaround: don't use -X with dump