1 files changed, 18 insertions, 9 deletions

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index d25bd224d370..77216742c178 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -26,8 +26,17 @@
  */
 struct anon_vma {
         spinlock_t lock;        /* Serialize access to vma list */
-#ifdef CONFIG_KSM
-        atomic_t ksm_refcount;
+#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
+
+        /*
+         * The external_refcount is taken by either KSM or page migration
+         * to take a reference to an anon_vma when there is no
+         * guarantee that the vma of page tables will exist for
+         * the duration of the operation. A caller that takes
+         * the reference is responsible for clearing up the
+         * anon_vma if they are the last user on release
+         */
+        atomic_t external_refcount;
 #endif
         /*
          * NOTE: the LSB of the head.next is set by
@@ -61,22 +70,22 @@ struct anon_vma_chain {
 };
 
 #ifdef CONFIG_MMU
-#ifdef CONFIG_KSM
-static inline void ksm_refcount_init(struct anon_vma *anon_vma)
+#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
+static inline void anonvma_external_refcount_init(struct anon_vma *anon_vma)
 {
-        atomic_set(&anon_vma->ksm_refcount, 0);
+        atomic_set(&anon_vma->external_refcount, 0);
 }
 
-static inline int ksm_refcount(struct anon_vma *anon_vma)
+static inline int anonvma_external_refcount(struct anon_vma *anon_vma)
 {
-        return atomic_read(&anon_vma->ksm_refcount);
+        return atomic_read(&anon_vma->external_refcount);
 }
 #else
-static inline void ksm_refcount_init(struct anon_vma *anon_vma)
+static inline void anonvma_external_refcount_init(struct anon_vma *anon_vma)
 {
 }
 
-static inline int ksm_refcount(struct anon_vma *anon_vma)
+static inline int anonvma_external_refcount(struct anon_vma *anon_vma)
 {
         return 0;
 }