fs: only assert on LOOKUP_RCU when built with CONFIG_DEBUG_VFS

Calls to the 2 modified routines are explicitly gated with checks for
the flag, so there is no use for this in production kernels.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://patch.msgid.link/20251229125751.826050-1-mjguzik@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: mjguzik

fs/namei.c

@@ -881,7 +881,7 @@ static bool try_to_unlazy(struct nameidata *nd)
 {
 	struct dentry *parent = nd->path.dentry;
 
-	BUG_ON(!(nd->flags & LOOKUP_RCU));
+	VFS_BUG_ON(!(nd->flags & LOOKUP_RCU));
 
 	if (unlikely(nd->depth && !legitimize_links(nd)))
 		goto out1;
@@ -916,7 +916,8 @@ static bool try_to_unlazy(struct nameidata *nd)
 static bool try_to_unlazy_next(struct nameidata *nd, struct dentry *dentry)
 {
 	int res;
-	BUG_ON(!(nd->flags & LOOKUP_RCU));
+
+	VFS_BUG_ON(!(nd->flags & LOOKUP_RCU));
 
 	if (unlikely(nd->depth && !legitimize_links(nd)))
 		goto out2;