[PATCH 1/2] mmotm: cpusetmm-update-tasks-mems_allowed-in-time-fix

[Lee Schermerhorn <lee.schermerhorn@hp.com>]

PATCH 1/2 cpusetmm-update-tasks-mems_allowed-in-time-fix

[forgot linux-mm in previous send.  sorry for repeat.  at least
it's only two patches...]

Against: 2.6.30-rc3-mmotm-090424-1814

The rework of mpol_new() to extract the adjusting of the node mask
to apply cpuset and mpol flags "context" breaks set_mempolicy() and
mbind() with MPOL_PREFERRED and a NULL nodemask--i.e., explicit local
allocation.  Fix this by adding the check for MPOL_PREFERRED and
empty node mask to mpol_new_mpolicy().

Remove the now unneeded 'nodes = NULL' from mpol_new().

Note that mpol_new_mempolicy() is always called with a non-NULL
'nodes' parameter now that it has been removed from mpol_new().
Therefore, we don't need to test nodes for NULL before testing
it for 'empty'.  However, just to be extra paranoid, add a 
VM_BUG_ON() to verify this assumption.

Tested on x86_64 with numactl-2.0.3-rc2+ regression test.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

 mm/mempolicy.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

Index: linux-2.6.30-rc3-mmotm-090424-1814/mm/mempolicy.c
===================================================================
--- linux-2.6.30-rc3-mmotm-090424-1814.orig/mm/mempolicy.c	2009-04-27 13:42:53.000000000 -0400
+++ linux-2.6.30-rc3-mmotm-090424-1814/mm/mempolicy.c	2009-04-28 13:32:32.000000000 -0400
@@ -182,8 +182,9 @@ static int mpol_new_bind(struct mempolic
 	return 0;
 }
 /*
- * This function is called after mpol_new(). The parameter -- nodes needn't
- * been check because mpol_new() has done it. Maybe this implement is ugly.
+ * This function is called after mpol_new().  mpol_new() has already validated
+ * the nodes parameter with respect to the policy mode and flags.  But, we
+ * need to handle an empty nodemaks with MPOL_PREFERRED here.
  *
  * We use task's alloc_lock to protect task's mems_allowed and mempolicy.
  * so this function should be called with task's alloc_lock held.
@@ -197,7 +198,10 @@ static int mpol_new_mempolicy(struct mem
 	if (pol == NULL)
 		return 0;
 
-	if (nodes) {
+	VM_BUG_ON(!nodes);
+	if (pol->mode == MPOL_PREFERRED && nodes_empty(*nodes))
+		nodes = NULL;	/* explicit local allocation */
+	else {
 		if (pol->flags & MPOL_F_RELATIVE_NODES)
 			mpol_relative_nodemask(&cpuset_context_nmask, nodes,
 					       &cpuset_current_mems_allowed);
@@ -243,7 +247,6 @@ static struct mempolicy *mpol_new(unsign
 			if (((flags & MPOL_F_STATIC_NODES) ||
 			     (flags & MPOL_F_RELATIVE_NODES)))
 				return ERR_PTR(-EINVAL);
-			nodes = NULL;	/* flag local alloc */
 		}
 	} else if (nodes_empty(*nodes))
 		return ERR_PTR(-EINVAL);