Merge git://git.kernel.org/pub/scm/linux/kernel/git/sam/kbuild-fixes

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 1383692ac5b..69407f85e10 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 */
 };