MFC 272550:

MFC 272550:

  Remove stray uma_mtx lock/unlock in zone_drain_wait()

  Callers of zone_drain_wait(M_WAITOK) do not need to hold (and were not)
  the uma_mtx, but we would attempt to unlock and relock the mutex if we
  had to sleep because the zone was already draining. The M_NOWAIT callers
  may hold the uma_mtx, but we do not sleep in that case.

git-svn-id: svn://svn.freebsd.org/base/stable/8@272725 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f