Use d_materialise_unique to splice dir dentries

When we're splicing in dentries in lookup we can be splicing the result
of changes on other nodes into a stale dcache.  The stale dcache might
contain dir entries and the dcache does not allow aliased directories.

Use d_materialise_unique() to splice in dir inodes so that we remove all
aliased dentries which must be stale.

We can still use d_splice_alias() for all other inode types.  Any
existing stale dentries will fail revalidation before they're used.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/dir.c

@@ -463,7 +463,18 @@ out:
 	else
 		inode = scoutfs_iget(sb, ino);
 
-	return d_splice_alias(inode, dentry);
+	/*
+	 * We can't splice dir aliases into the dcache.  dir entries
+	 * might have changed on other nodes so our dcache could still
+	 * contain them, rather than having been moved in rename.  For
+	 * dirs, we use d_materialize_unique to remove any existing
+	 * aliases which must be stale.  Our inode numbers aren't reused
+	 * so inodes pointed to by entries can't change types.
+	 */
+	if (!IS_ERR_OR_NULL(inode) && S_ISDIR(inode->i_mode))
+		return d_materialise_unique(dentry, inode);
+	else
+		return d_splice_alias(inode, dentry);
 }
 
 /*