ext4: fix double unlock buffer mess during fs-resize

bh_submit_read() is responsible for unlock bh on endio. In addition,
we need to use bh_uptodate_or_lock() to avoid races.

Signed-off-by: Dmitry Monakhov <[e-mail]>
Signed-off-by: "Theodore Ts'o" <[e-mail]>

fs/ext4/resize.c

···
 	struct buffer_head *bh = sb_getblk(sb, block);
 	if (!bh)
 		return NULL;
-
-	if (bitmap_uptodate(bh))
-		return bh;
-
-	lock_buffer(bh);
-	if (bh_submit_read(bh) < 0) {
-		unlock_buffer(bh);
-		brelse(bh);
-		return NULL;
+	if (!bh_uptodate_or_lock(bh)) {
+		if (bh_submit_read(bh) < 0) {
+			brelse(bh);
+			return NULL;
+		}
 	}
-	unlock_buffer(bh);
 
 	return bh;
 }