diff --git a/fs/inode.c b/fs/inode.c
index c99163b..033529e 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1551,6 +1551,8 @@
 	 * Btrfs), but since we touch atime while walking down the path we
 	 * really don't care if we failed to update the atime of the file,
 	 * so just ignore the return value.
+	 * We may also fail on filesystems that have the ability to make parts
+	 * of the fs read only, e.g. subvolumes in Btrfs.
 	 */
 	update_time(inode, &now, S_ATIME);
 	mnt_drop_write(mnt);