diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 67d8bec55fb7..e5fc3788c007 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4042,6 +4042,10 @@ void ext4_set_aops(struct inode *inode)
  * because it might have data in pagecache (eg, if called from ext4_zero_range,
  * ext4_punch_hole, etc) which needs to be properly zeroed out. Otherwise a
  * racing writeback can come later and flush the stale pagecache to disk.
+ *
+ * Return the loaded bh if it actually needs zeroing - in written, dirty
+ * unwritten, or delalloc state. Return NULL if it's clean (i.e., a hole or
+ * a clean unwritten block).
  */
 static struct buffer_head *ext4_load_tail_bh(struct inode *inode, loff_t from)
 {
@@ -4083,7 +4087,12 @@ static struct buffer_head *ext4_load_tail_bh(struct inode *inode, loff_t from)
 		err = ext4_get_block(inode, iblock, bh, 0);
 		if (err < 0)
 			goto unlock;
-		/* unmapped? It's a hole - nothing to do */
+		/*
+		 * It's a hole or a clean unwritten block - nothing to do.
+		 * Note that a lookup-only get_block (without
+		 * EXT4_GET_BLOCKS_CREATE) never sets BH_Mapped for clean
+		 * unwritten extents.
+		 */
 		if (!buffer_mapped(bh)) {
 			BUFFER_TRACE(bh, "still unmapped");
 			goto unlock;