panic: assertion: layer2->zone == zone in hammer_blockmap_free

[YONETANI Tomokazu <qhwt+dfly@xxxxxxxxxx>]

Hi.
Caught this panic on latest DragonFly_RELEASE_2_0 (minus the fix to
vfs_subr.c, but the machine has less than 2G RAM), when I tried to
destroy a PFS slave on HAMMER filesystem.  The PFS hasn't been actively
used, only to try mirror-copy of another PFS, which is used as /usr/obj.
The panic also occurs when I try to reblock this PFS, but no problem
to upgrade to a PFS master.  I don't have a problem reblocking or pruning
other PFS's or HAMMER filesystem containing them.

The backtrace looks like this:
(kgdb) bt
#0  dumpsys () at ./machine/thread.h:83
#1  0xc0198cbd in boot (howto=260)
    at /home/source/dragonfly/R2_0/src/sys/kern/kern_shutdown.c:375
#2  0xc0198f80 in panic (fmt=0xc02d6a9f "assertion: %s in %s")
    at /home/source/dragonfly/R2_0/src/sys/kern/kern_shutdown.c:800
#3  0xc02508cf in hammer_blockmap_free (trans=0xd5fc2a88,
    zone_offset=10376293547717272640, bytes=128)
    at /home/source/dragonfly/R2_0/src/sys/vfs/hammer/hammer_blockmap.c:734
#4  0xc025e8df in hammer_delete_at_cursor (cursor=0xd5fc2894, delete_flags=2,
    delete_tid=0, delete_ts=1217680974, track=1, stat_bytes=0x0)
    at /home/source/dragonfly/R2_0/src/sys/vfs/hammer/hammer_object.c:2103
#5  0xc0262d78 in hammer_pfs_rollback (trans=0xd5fc2a88, pfsm=0xcc2e45a8,
    trunc_tid=0)
    at /home/source/dragonfly/R2_0/src/sys/vfs/hammer/hammer_pfs.c:403
#6  0xc0262ee0 in hammer_ioc_destroy_pseudofs (trans=0xd5fc2a88,
    ip=0xd59b7cd0, pfs=0xd5fc2c1c)
    at /home/source/dragonfly/R2_0/src/sys/vfs/hammer/hammer_pfs.c:244
#7  0xc025b748 in hammer_ioctl (ip=0xd59b7cd0, com=3224135691,
    data=0xd5fc2c1c "", fflag=1, cred=0xd5c13d98)
    at /home/source/dragonfly/R2_0/src/sys/vfs/hammer/hammer_ioctl.c:100
#8  0xc026ab2c in hammer_vop_ioctl (ap=0xd5fc2ae0)
    at /home/source/dragonfly/R2_0/src/sys/vfs/hammer/hammer_vnops.c:2011
#9  0xc01ec326 in vop_ioctl (ops=0xd57993b0, vp=0xd56dcba8,
    command=3224135691, data=0xd5fc2c1c "", fflag=1, cred=0xd5c13d98)
    at /home/source/dragonfly/R2_0/src/sys/kern/vfs_vopops.c:372
#10 0xc01eb98c in vn_ioctl (fp=0xcfecd758, com=3224135691, data=0xd5fc2c1c "",
    ucred=0xd5c13d98)
    at /home/source/dragonfly/R2_0/src/sys/kern/vfs_vnops.c:1006
#11 0xc01b8268 in mapped_ioctl (fd=3, com=3224135691,
    uspc_data=0xbfbffb90 <Address 0xbfbffb90 out of bounds>, map=0x0)
    at /home/source/dragonfly/R2_0/src/sys/sys/file2.h:87
#12 0xc01b82f0 in sys_ioctl (uap=0xd5fc2cf0)
    at /home/source/dragonfly/R2_0/src/sys/kern/sys_generic.c:525
#13 0xc02b24ef in syscall2 (frame=0xd5fc2d40)
    at /home/source/dragonfly/R2_0/src/sys/platform/pc32/i386/trap.c:1384
#14 0xc029ed26 in Xint0x80_syscall ()
    at /home/source/dragonfly/R2_0/src/sys/platform/pc32/i386/exception.s:876
#15 0x080511ec in ?? ()

The kernel dump has been uploaded as ~y0netan1/crash/{kernel,vmcore}.13
on my leaf account.

Cheers.