9p: set page uptodate when required in write_end()

Commit 77469c3f570 prevented setting the page as uptodate when we wrote
the right amount of data, fix that.

Fixes: 77469c3f570 ("9p: saner ->write_end() on failing copy into non-uptodate page")
Reviewed-by: Jan Kara <jack@suse.com>
Signed-off-by: Alexander Levin <alexander.levin@verizon.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/9p/vfs_addr.c

@@ -310,9 +310,13 @@ static int v9fs_write_end(struct file *filp, struct address_space *mapping,
 
 	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);
 
-	if (unlikely(copied < len && !PageUptodate(page))) {
-		copied = 0;
-		goto out;
+	if (!PageUptodate(page)) {
+		if (unlikely(copied < len)) {
+			copied = 0;
+			goto out;
+		} else if (len == PAGE_SIZE) {
+			SetPageUptodate(page);
+		}
 	}
 	/*
 	 * No need to use i_size_read() here, the i_size