Add a new mutex for use in adding and removing of memory blocks.  This
is needed to avoid any race conditions in which the same memory block could
be added and removed at the same time.
Signed-off-by: NNathan Fontenot <nfont@austin.ibm.com>
Reviewed-by: NRobin Holt <holt@sgi.com>
Reviewed-By: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>