GIT: unionfs2-2.6.27.y: tmpfs: fix oops on mounts with mpol=default

[Erez Zadok]

commit 6af438190daa4b53c1570c09244f99f2db447f78
Author: Ravikiran G Thirumalai <kiran at scalex86.org>
Date:   Tue Mar 23 13:35:28 2010 -0700

    tmpfs: fix oops on mounts with mpol=default
    
    commit 413b43deab8377819aba1dbad2abf0c15d59b491 upstream.
    
    Fix an 'oops' when a tmpfs mount point is mounted with the mpol=default
    mempolicy.
    
    Upon remounting a tmpfs mount point with 'mpol=default' option, the mount
    code crashed with a null pointer dereference.  The initial problem report
    was on 2.6.27, but the problem exists in mainline 2.6.34-rc as well.  On
    examining the code, we see that mpol_new returns NULL if default mempolicy
    was requested.  This 'NULL' mempolicy is accessed to store the node mask
    resulting in oops.
    
    The following patch fixes it.
    
    Signed-off-by: Ravikiran Thirumalai <kiran at scalex86.org>
    Signed-off-by: KOSAKI Motohiro <kosaki.motohiro at jp.fujitsu.com>
    Cc: Christoph Lameter <cl at linux-foundation.org>
    Cc: Mel Gorman <mel at csn.ul.ie>
    Acked-by: Lee Schermerhorn <lee.schermerhorn at hp.com>
    Cc: Hugh Dickins <hugh.dickins at tiscali.co.uk>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 7acf81c..b732aca 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2049,10 +2049,15 @@ int mpol_parse_str(char *str, struct mempolicy **mpol, int no_context)
 			goto out;
 		mode = MPOL_PREFERRED;
 		break;
-
+	case MPOL_DEFAULT:
+		/*
+		 * Insist on a empty nodelist
+		 */
+		if (!nodelist)
+			err = 0;
+		goto out;
 	/*
 	 * case MPOL_BIND:    mpol_new() enforces non-empty nodemask.
-	 * case MPOL_DEFAULT: mpol_new() enforces empty nodemask, ignores flags.
 	 */
 	}