1 files changed, 32 insertions, 2 deletions

diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index 3d535d594826..3dd88539a0e6 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -335,6 +335,37 @@ not_enough_page:
 }
 
 /**
+ * swap_cgroup_cmpxchg - cmpxchg mem_cgroup's id for this swp_entry.
+ * @end: swap entry to be cmpxchged
+ * @old: old id
+ * @new: new id
+ *
+ * Returns old id at success, 0 at failure.
+ * (There is no mem_cgroup useing 0 as its id)
+ */
+unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
+                                        unsigned short old, unsigned short new)
+{
+        int type = swp_type(ent);
+        unsigned long offset = swp_offset(ent);
+        unsigned long idx = offset / SC_PER_PAGE;
+        unsigned long pos = offset & SC_POS_MASK;
+        struct swap_cgroup_ctrl *ctrl;
+        struct page *mappage;
+        struct swap_cgroup *sc;
+
+        ctrl = &swap_cgroup_ctrl[type];
+
+        mappage = ctrl->map[idx];
+        sc = page_address(mappage);
+        sc += pos;
+        if (cmpxchg(&sc->id, old, new) == old)
+                return old;
+        else
+                return 0;
+}
+
+/**
  * swap_cgroup_record - record mem_cgroup for this swp_entry.
  * @ent: swap entry to be recorded into
  * @mem: mem_cgroup to be recorded
@@ -358,8 +389,7 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
         mappage = ctrl->map[idx];
         sc = page_address(mappage);
         sc += pos;
-        old = sc->id;
-        sc->id = id;
+        old = xchg(&sc->id, id);
 
         return old;
 }