[PATCH v3 04/14] mm/mempolicy: allow preferred code to take a nodemask

[Feng Tang <feng.tang@intel.com>]

From: Dave Hansen <dave.hansen@linux.intel.com>

Create a helper function (mpol_new_preferred_many()) which is usable
both by the old, single-node MPOL_PREFERRED and the new
MPOL_PREFERRED_MANY.

Enforce the old single-node MPOL_PREFERRED behavior in the "new"
version of mpol_new_preferred() which calls mpol_new_preferred_many().

v3:
  * fix a stack overflow caused by emty nodemask (Feng)

Link: https://lore.kernel.org/r/20200630212517.308045-5-ben.widawsky@intel.com
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Signed-off-by: Feng Tang <feng.tang@intel.com>
---
 mm/mempolicy.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 79258b2..19ec954 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -203,17 +203,34 @@ static int mpol_new_interleave(struct mempolicy *pol, const nodemask_t *nodes)
 	return 0;
 }
 
-static int mpol_new_preferred(struct mempolicy *pol, const nodemask_t *nodes)
+static int mpol_new_preferred_many(struct mempolicy *pol,
+				   const nodemask_t *nodes)
 {
 	if (!nodes)
 		pol->flags |= MPOL_F_LOCAL;	/* local allocation */
 	else if (nodes_empty(*nodes))
 		return -EINVAL;			/*  no allowed nodes */
 	else
-		pol->v.preferred_nodes = nodemask_of_node(first_node(*nodes));
+		pol->v.preferred_nodes = *nodes;
 	return 0;
 }
 
+static int mpol_new_preferred(struct mempolicy *pol, const nodemask_t *nodes)
+{
+	if (nodes) {
+		/* MPOL_PREFERRED can only take a single node: */
+		nodemask_t tmp;
+
+		if (nodes_empty(*nodes))
+			return -EINVAL;
+
+		tmp = nodemask_of_node(first_node(*nodes));
+		return mpol_new_preferred_many(pol, &tmp);
+	}
+
+	return mpol_new_preferred_many(pol, NULL);
+}
+
 static int mpol_new_bind(struct mempolicy *pol, const nodemask_t *nodes)
 {
 	if (nodes_empty(*nodes))
-- 
2.7.4