ubifs: Set page uptodate in the correct place

Page cache reads are lockless, so setting the freshly allocated page
uptodate before we've overwritten it with the data it's supposed to have
in it will allow a simultaneous reader to see old data.  Move the call
to SetPageUptodate into ubifs_write_end(), which is after we copied the
new data into the page.

Fixes: 1e51764 ("UBIFS: add new flash file system")
Cc: stable@vger.kernel.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/file.c

@@ -261,9 +261,6 @@ static int write_begin_slow(struct address_space *mapping,
 				return err;
 			}
 		}
-
-		SetPageUptodate(page);
-		ClearPageError(page);
 	}
 
 	if (PagePrivate(page))
@@ -463,9 +460,6 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
 				return err;
 			}
 		}
-
-		SetPageUptodate(page);
-		ClearPageError(page);
 	}
 
 	err = allocate_budget(c, page, ui, appending);
@@ -475,10 +469,8 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
 		 * If we skipped reading the page because we were going to
 		 * write all of it, then it is not up to date.
 		 */
-		if (skipped_read) {
+		if (skipped_read)
 			ClearPageChecked(page);
-			ClearPageUptodate(page);
-		}
 		/*
 		 * Budgeting failed which means it would have to force
 		 * write-back but didn't, because we set the @fast flag in the
@@ -569,6 +561,9 @@ static int ubifs_write_end(struct file *file, struct address_space *mapping,
 		goto out;
 	}
 
+	if (len == PAGE_SIZE)
+		SetPageUptodate(page);
+
 	if (!PagePrivate(page)) {
 		attach_page_private(page, (void *)1);
 		atomic_long_inc(&c->dirty_pg_cnt);