mount -t tmpfs -o mpol=: check nodes online

Randy Dunlap reports that a tmpfs, mounted with NUMA mpol= specifying an
offline node, crashes as soon as data is allocated upon it.  Now restrict it
to online nodes, where before it restricted to MAX_NUMNODES.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Robin Holt <holt@sgi.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Andi Kleen <ak@suse.de>
Tested-and-acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>