panic: assertion: volume->io.lock.refs == 0 in hammer_unload_volume

[Thomas Nikolajsen <thomas.nikolajsen@xxxxxxx>]

I've got this panic multiple times at shutdown;
this is on nfs server using hammer for exports.

Crash dump on leaf in crash/hammer/ask/*.4.

Panic only seen after running buildworld on client w/ usr/src & usr/obj nfs mounted;
no problem when client uses local file system (e.g. hammer) for /usr/obj.

 -thomas
-
(kgdb) bt
#0  dumpsys () at ./machine/thread.h:83
#1  0xc01a2226 in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:375
#2  0xc01a2347 in panic (fmt=0xc0322fcb "from debugger")
    at /usr/src/sys/kern/kern_shutdown.c:800
#3  0xc014a059 in db_panic (addr=-1070669340, have_addr=0, count=-1, 
    modif=0xc4d6aa08 "") at /usr/src/sys/ddb/db_command.c:447
#4  0xc014a6c4 in db_command_loop () at /usr/src/sys/ddb/db_command.c:343
#5  0xc014cc3c in db_trap (type=3, code=0) at /usr/src/sys/ddb/db_trap.c:71
#6  0xc02ee337 in kdb_trap (type=3, code=0, regs=0xc4d6ab00)
    at /usr/src/sys/platform/pc32/i386/db_interface.c:148
#7  0xc02fd586 in trap (frame=0xc4d6ab00)
    at /usr/src/sys/platform/pc32/i386/trap.c:842
#8  0xc02ef047 in calltrap ()
    at /usr/src/sys/platform/pc32/i386/exception.s:785
#9  0xc02ee1e4 in Debugger (msg=0xc0328dd7 "panic") at ./cpu/cpufunc.h:73
#10 0xc01a233e in panic (fmt=0xd208c47a "assertion: %s in %s")
    at /usr/src/sys/kern/kern_shutdown.c:798
#11 0xd2079819 in ?? ()
#12 0xd2077daf in ?? ()
#13 0xd206e5a1 in ?? ()
#14 0xd206e60a in ?? ()
#15 0xc01ef04c in dounmount (mp=0xc0e1c984, flags=524288)
    at /usr/src/sys/kern/vfs_syscalls.c:705
#16 0xc01e7f1a in vfs_umountall_callback (mp=0xc7a57c88, data=0x0)
    at /usr/src/sys/kern/vfs_subr.c:1619
#17 0xc01eac41 in mountlist_scan (
    callback=0xc01e7f07 <vfs_umountall_callback>, data=0x0, 
    how=<value optimized out>) at /usr/src/sys/kern/vfs_mount.c:816
#18 0xc01e7507 in vfs_unmountall () at /usr/src/sys/kern/vfs_subr.c:1608
#19 0xc01a2086 in boot (howto=0) at /usr/src/sys/kern/kern_shutdown.c:363
#20 0xc01a23e1 in sys_reboot (uap=0xc4d6acf0)
    at /usr/src/sys/kern/kern_shutdown.c:192
#21 0xc02fcf0d in syscall2 (frame=0xc4d6ad40)
    at /usr/src/sys/platform/pc32/i386/trap.c:1384
#22 0xc02ef0f6 in Xint0x80_syscall ()
    at /usr/src/sys/platform/pc32/i386/exception.s:876
#23 0x0804fa10 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)