3 files changed, 12 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6e695eaab4ce..866a3dbe5c75 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1104,6 +1104,9 @@ extern struct vm_area_struct *copy_vma(struct vm_area_struct **,
         unsigned long addr, unsigned long len, pgoff_t pgoff);
 extern void exit_mmap(struct mm_struct *);
 
+extern int mm_take_all_locks(struct mm_struct *mm);
+extern void mm_drop_all_locks(struct mm_struct *mm);
+
 #ifdef CONFIG_PROC_FS
 /* From fs/proc/base.c. callers must _not_ hold the mm's exe_file_lock */
 extern void added_exe_file_vma(struct mm_struct *mm);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index a81d81890422..a39b38ccdc97 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -20,6 +20,7 @@
  */
 #define AS_EIO          (__GFP_BITS_SHIFT + 0)  /* IO error on async write */
 #define AS_ENOSPC       (__GFP_BITS_SHIFT + 1)  /* ENOSPC on async write */
+#define AS_MM_ALL_LOCKS (__GFP_BITS_SHIFT + 2)  /* under mm_take_all_locks() */
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
 {
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 */
 };