mempolicy: fix get_mempolicy() for relative and static nodes

Discovered while testing other mempolicy changes:

get_mempolicy() does not handle static/relative mode flags correctly.
Return the value that the user specified so that it can be restored
via set_mempolicy() if desired.
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Ravikiran Thirumalai <kiran@scalex86.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mempolicy.c

@@ -806,10 +806,14 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
 
 	err = 0;
 	if (nmask) {
+		if (mpol_store_user_nodemask(pol)) {
+			*nmask = pol->w.user_nodemask;
+		} else {
 			task_lock(current);
 			get_policy_nodemask(pol, nmask);
 			task_unlock(current);
 		}
+	}
 
  out:
 	mpol_cond_put(pol);