blocks on a pmap lock, pmap_release() might proceed in parallel and
destroy the pmap mutex, since unlocked pv lock allows to remove pv
entry owned by the pmap.
For now, gate the pmap_release() on write-locked pvh_global_lock.
Since pmap_ts_release() does not unlock the global lock,
pmap_release() would not destroy pmap mutex until the
pmap_ts_referenced() finished. We cannot enter pmap_ts_referenced()
and encounter a pv entry for the destroyed pmap if pmap_release()
passed the global lock gate, since pmap_remove_pages() would finish
earlier.
Reported by: jeff, pho
Reviewed by: alc
Tested by: pho
Sponsored by: The FreeBSD Foundation
d91f339823