[RFT PATCH 1/2] Revert "fb_defio: fix for non-dirty ptes"

@@ -155,41 +155,25 @@ static void fb_deferred_io_work(struct work_struct *work)
 {
 	struct fb_info *info = container_of(work, struct fb_info,
 						deferred_work.work);
+	struct list_head *node, *next;
+	struct page *cur;
 	struct fb_deferred_io *fbdefio = info->fbdefio;
-	struct page *page, *tmp_page;
-	struct list_head *node, *tmp_node;
-	struct list_head non_dirty;
-
-	INIT_LIST_HEAD(&non_dirty);
 
 	/* here we mkclean the pages, then do all deferred IO */
 	mutex_lock(&fbdefio->lock);
-	list_for_each_entry_safe(page, tmp_page, &fbdefio->pagelist, lru) {
-		lock_page(page);
-		/*
-		 * The workqueue callback can be triggered after a
-		 * ->page_mkwrite() call but before the PTE has been marked
-		 * dirty. In this case page_mkclean() won't "rearm" the page.
-		 *
-		 * To avoid this, remove those "non-dirty" pages from the
-		 * pagelist before calling the driver's callback, then add
-		 * them back to get processed on the next work iteration.
-		 * At that time, their PTEs will hopefully be dirty for real.
-		 */
-		if (!page_mkclean(page))
-			list_move_tail(&page->lru, &non_dirty);
-		unlock_page(page);
+	list_for_each_entry(cur, &fbdefio->pagelist, lru) {
+		lock_page(cur);
+		page_mkclean(cur);
+		unlock_page(cur);
 	}
 
 	/* driver's callback with pagelist */
 	fbdefio->deferred_io(info, &fbdefio->pagelist);
 
-	/* clear the list... */
-	list_for_each_safe(node, tmp_node, &fbdefio->pagelist) {
+	/* clear the list */
+	list_for_each_safe(node, next, &fbdefio->pagelist) {
 		list_del(node);
 	}
-	/* ... and add back the "non-dirty" pages to the list */
-	list_splice_tail(&non_dirty, &fbdefio->pagelist);
 	mutex_unlock(&fbdefio->lock);
 }
 

@@ -218,20 +202,12 @@ EXPORT_SYMBOL_GPL(fb_deferred_io_open);
 void fb_deferred_io_cleanup(struct fb_info *info)
 {
 	struct fb_deferred_io *fbdefio = info->fbdefio;
-	struct list_head *node, *tmp_node;
 	struct page *page;
 	int i;
 
 	BUG_ON(!fbdefio);
 	flush_delayed_work(&info->deferred_work);
 
-	/*  the list may have still some non-dirty pages at this point */
-	mutex_lock(&fbdefio->lock);
-	list_for_each_safe(node, tmp_node, &fbdefio->pagelist) {
-		list_del(node);
-	}
-	mutex_unlock(&fbdefio->lock);
-
 	/* clear out the mapping that we setup */
 	for (i = 0 ; i < info->fix.smem_len; i += PAGE_SIZE) {
 		page = fb_deferred_io_page(info, i);

@@ -100,6 +100,16 @@ static int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
 	/* protect against the workqueue changing the page list */
 	mutex_lock(&fbdefio->lock);
 
+	/*
+	 * We want the page to remain locked from ->page_mkwrite until
+	 * the PTE is marked dirty to avoid page_mkclean() being called
+	 * before the PTE is updated, which would leave the page ignored
+	 * by defio.
+	 * Do this by locking the page here and informing the caller
+	 * about it with VM_FAULT_LOCKED.
+	 */
+	lock_page(page);
+
 	/* we loop through the pagelist before adding in order
 	to keep the pagelist sorted */
 	list_for_each_entry(cur, &fbdefio->pagelist, lru) {

@@ -121,7 +131,7 @@ page_already_added:
 
 	/* come back after delay to process the deferred IO */
 	schedule_delayed_work(&info->deferred_work, fbdefio->delay);
-	return 0;
+	return VM_FAULT_LOCKED;
 }
 
 static const struct vm_operations_struct fb_deferred_io_vm_ops = {