page_writeback: put account_page_redirty() after set_page_dirty()

Helper account_page_redirty() fixes dirty pages counter for redirtied
pages.  This patch puts it after dirtying and prevents temporary
underflows of dirtied pages counters on zone/bdi and current->nr_dirtied.

Signed-off-by: Konstantin Khebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/btrfs/extent_io.c

@@ -1407,8 +1407,8 @@ int extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end)
 	while (index <= end_index) {
 		page = find_get_page(inode->i_mapping, index);
 		BUG_ON(!page); /* Pages should be in the extent_io_tree */
-		account_page_redirty(page);
 		__set_page_dirty_nobuffers(page);
+		account_page_redirty(page);
 		page_cache_release(page);
 		index++;
 	}

mm/page-writeback.c

@@ -2168,9 +2168,12 @@ EXPORT_SYMBOL(account_page_redirty);
  */
 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
 {
+	int ret;
+
 	wbc->pages_skipped++;
+	ret = __set_page_dirty_nobuffers(page);
 	account_page_redirty(page);
-	return __set_page_dirty_nobuffers(page);
+	return ret;
 }
 EXPORT_SYMBOL(redirty_page_for_writepage);