Re: [PATCH 2/7] mark root hnode explicitly

Point, and that one is IMO enough to give up on using ->flags for
that.  How about simply

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 3f985f29ef30..d14048e38b5c 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c

@@ -84,6 +84,7 @@ struct tc_u_hnode {
  	int			refcnt;
  	unsigned int		divisor;
  	struct idr		handle_idr;
+	bool			is_root;
  	struct rcu_head		rcu;
  	u32			flags;
  	/* The 'ht' field MUST be the last field in structure to allow for

@@ -377,6 +378,7 @@ static int u32_init(struct tcf_proto *tp)
  	root_ht->refcnt++;
  	root_ht->handle = tp_c ? gen_new_htid(tp_c, root_ht) : 0x80000000;
  	root_ht->prio = tp->prio;
+	root_ht->is_root = true;
  	idr_init(&root_ht->handle_idr);
  
  	if (tp_c == NULL) {

@@ -693,7 +695,7 @@ static int u32_delete(struct tcf_proto *tp, void *arg, bool *last,
  		goto out;
  	}
  
-	if (root_ht == ht) {
+	if (ht->is_root) {
  		NL_SET_ERR_MSG_MOD(extack, "Not allowed to delete root node");
  		return -EINVAL;
  	}

@@ -795,6 +797,10 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
  				NL_SET_ERR_MSG_MOD(extack, "Link hash table not found");
  				return -EINVAL;
  			}
+			if (ht_down->is_root) {
+				NL_SET_ERR_MSG_MOD(extack, "Not linking to root node");
+				return -EINVAL;
+			}
  			ht_down->refcnt++;