diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 970c8ec1a05bfc2620351279708a30d8f465ebab..91ec4b40ebfe2b722a02ace1798ff17f7447df83 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -512,13 +512,22 @@ prototypes:
 	void (*close)(struct vm_area_struct*);
 	struct page *(*fault)(struct vm_area_struct*, struct fault_data *);
 	struct page *(*nopage)(struct vm_area_struct*, unsigned long, int *);
+	int (*page_mkwrite)(struct vm_area_struct *, struct page *);
 
 locking rules:
-		BKL	mmap_sem
+		BKL	mmap_sem	PageLocked(page)
 open:		no	yes
 close:		no	yes
 fault:		no	yes
 nopage:		no	yes
+page_mkwrite:	no	yes		no
+
+	->page_mkwrite() is called when a previously read-only page is
+about to become writeable. The file system is responsible for
+protecting against truncate races. Once appropriate action has been
+taking to lock out truncate, the page range should be verified to be
+within i_size. The page mapping should also be checked that it is not
+NULL.
 
 ================================================================================
 			Dubious stuff