1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 1383692ac5bd..69407f85e10b 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -26,6 +26,14 @@
  */
 struct anon_vma {
         spinlock_t lock;        /* Serialize access to vma list */
+        /*
+         * NOTE: the LSB of the head.next is set by
+         * mm_take_all_locks() _after_ taking the above lock. So the
+         * head must only be read/written after taking the above lock
+         * to be sure to see a valid next pointer. The LSB bit itself
+         * is serialized by a system wide lock only visible to
+         * mm_take_all_locks() (mm_all_locks_mutex).
+         */
         struct list_head head;  /* List of private "related" vmas */
 };