1 files changed, 42 insertions, 0 deletions

diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index 3d535d594826..6c0081441a32 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -284,6 +284,7 @@ static DEFINE_MUTEX(swap_cgroup_mutex);
 struct swap_cgroup_ctrl {
         struct page **map;
         unsigned long length;
+        spinlock_t      lock;
 };
 
 struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];
@@ -335,6 +336,43 @@ 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;
+        unsigned long flags;
+        unsigned short retval;
+
+        ctrl = &swap_cgroup_ctrl[type];
+
+        mappage = ctrl->map[idx];
+        sc = page_address(mappage);
+        sc += pos;
+        spin_lock_irqsave(&ctrl->lock, flags);
+        retval = sc->id;
+        if (retval == old)
+                sc->id = new;
+        else
+                retval = 0;
+        spin_unlock_irqrestore(&ctrl->lock, flags);
+        return retval;
+}
+
+/**
  * swap_cgroup_record - record mem_cgroup for this swp_entry.
  * @ent: swap entry to be recorded into
  * @mem: mem_cgroup to be recorded
@@ -352,14 +390,17 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
         struct page *mappage;
         struct swap_cgroup *sc;
         unsigned short old;
+        unsigned long flags;
 
         ctrl = &swap_cgroup_ctrl[type];
 
         mappage = ctrl->map[idx];
         sc = page_address(mappage);
         sc += pos;
+        spin_lock_irqsave(&ctrl->lock, flags);
         old = sc->id;
         sc->id = id;
+        spin_unlock_irqrestore(&ctrl->lock, flags);
 
         return old;
 }
@@ -411,6 +452,7 @@ int swap_cgroup_swapon(int type, unsigned long max_pages)
         mutex_lock(&swap_cgroup_mutex);
         ctrl->length = length;
         ctrl->map = array;
+        spin_lock_init(&ctrl->lock);
         if (swap_cgroup_prepare(type)) {
                 /* memory shortage */
                 ctrl->map = NULL;