panic: uma_small_alloc: free page still has mappings!

sparc64 SMP machine running 7.0 panicked a few minutes after adding
load with:

panic: uma_small_alloc: free page still has mappings!
cpuid = 0
KDB: enter: panic
[thread pid 9124 tid 100318 ]
Stopped at      kdb_enter+0x3c: ta              %xcc, 1
db> wh
Tracing pid 9124 tid 100318 td 0xfffff800f6fb2720
panic() at panic+0x164
uma_small_alloc() at uma_small_alloc+0x9c
slab_zalloc() at slab_zalloc+0x98
uma_zone_slab() at uma_zone_slab+0x12c
uma_zalloc_bucket() at uma_zalloc_bucket+0x16c
uma_zalloc_arg() at uma_zalloc_arg+0x374
malloc() at malloc+0x114
allocbuf() at allocbuf+0x208
getblk() at getblk+0x598
breadn() at breadn+0x58
bread() at bread+0x20
ffs_blkatoff() at ffs_blkatoff+0x64
ufs_direnter() at ufs_direnter+0x444
ufs_makeinode() at ufs_makeinode+0x460
ufs_create() at ufs_create+0x30
VOP_CREATE_APV() at VOP_CREATE_APV+0xb4
vn_open_cred() at vn_open_cred+0x188
vn_open() at vn_open+0x18
kern_open() at kern_open+0x8c
open() at open+0x14
syscall() at syscall+0x2dc
-- syscall (5, FreeBSD ELF64, open) %o7=0x4034d5b8 --

Kris