tmpfs: mpol=bind:0 don't cause mount error.

Currently, following mount operation cause mount error.

% mount -t tmpfs -ompol=bind:0 none /tmp

Because commit 71fe804b (mempolicy: use struct mempolicy pointer in
shmem_sb_info) corrupted MPOL_BIND parse code.

This patch restore the needed one.
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Ravikiran Thirumalai <kiran@scalex86.org>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Acked-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mempolicy.c

@@ -2222,9 +2222,13 @@ int mpol_parse_str(char *str, struct mempolicy **mpol, int no_context)
 		if (!nodelist)
 			err = 0;
 		goto out;
+	case MPOL_BIND:
 		/*
-	 * case MPOL_BIND:    mpol_new() enforces non-empty nodemask.
+		 * Insist on a nodelist
 		 */
+		if (!nodelist)
+			goto out;
+		err = 0;
 	}
 
 	mode_flags = 0;