mm: Update file times from fault path only if .page_mkwrite is not set

Filesystems wanting to properly support freezing need to have control
when file_update_time() is called. After pushing file_update_time()
to all relevant .page_mkwrite implementations we can just stop calling
file_update_time() when filesystem implements .page_mkwrite.
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

mm/memory.c

@@ -2638,6 +2638,9 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		if (!page_mkwrite) {
 			wait_on_page_locked(dirty_page);
 			set_page_dirty_balance(dirty_page, page_mkwrite);
+			/* file_update_time outside page_lock */
+			if (vma->vm_file)
+				file_update_time(vma->vm_file);
 		}
 		put_page(dirty_page);
 		if (page_mkwrite) {
@@ -2655,10 +2658,6 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			}
 		}
 
-		/* file_update_time outside page_lock */
-		if (vma->vm_file)
-			file_update_time(vma->vm_file);
-
 		return ret;
 	}
 
@@ -3327,12 +3326,13 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 
 	if (dirty_page) {
 		struct address_space *mapping = page->mapping;
+		int dirtied = 0;
 
 		if (set_page_dirty(dirty_page))
-			page_mkwrite = 1;
+			dirtied = 1;
 		unlock_page(dirty_page);
 		put_page(dirty_page);
-		if (page_mkwrite && mapping) {
+		if ((dirtied || page_mkwrite) && mapping) {
 			/*
 			 * Some device drivers do not set page.mapping but still
 			 * dirty their pages
@@ -3341,7 +3341,7 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 		}
 
 		/* file_update_time outside page_lock */
-		if (vma->vm_file)
+		if (vma->vm_file && !page_mkwrite)
 			file_update_time(vma->vm_file);
 	} else {
 		unlock_page(vmf.page);