net: sched: use reference counting for tcf blocks on rules update

In order to remove dependency on rtnl lock on rules update path, always
take reference to block while using it on rules update path. Change
tcf_block_get() error handling to properly release block with reference
counting, instead of just destroying it, in order to accommodate potential
concurrent users.
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_api.c

@@ -622,7 +622,7 @@ static struct tcf_block *tcf_block_find(struct net *net, struct Qdisc **q,
 	int err = 0;
 
 	if (ifindex == TCM_IFINDEX_MAGIC_BLOCK) {
-		block = tcf_block_lookup(net, block_index);
+		block = tcf_block_refcnt_get(net, block_index);
 		if (!block) {
 			NL_SET_ERR_MSG(extack, "Block of given index was not found");
 			return ERR_PTR(-EINVAL);
@@ -702,6 +702,14 @@ static struct tcf_block *tcf_block_find(struct net *net, struct Qdisc **q,
 			err = -EOPNOTSUPP;
 			goto errout_qdisc;
 		}
+
+		/* Always take reference to block in order to support execution
+		 * of rules update path of cls API without rtnl lock. Caller
+		 * must release block when it is finished using it. 'if' block
+		 * of this conditional obtain reference to block by calling
+		 * tcf_block_refcnt_get().
+		 */
+		refcount_inc(&block->refcnt);
 	}
 
 	return block;
@@ -716,6 +724,9 @@ static struct tcf_block *tcf_block_find(struct net *net, struct Qdisc **q,
 
 static void tcf_block_release(struct Qdisc *q, struct tcf_block *block)
 {
+	if (!IS_ERR_OR_NULL(block))
+		tcf_block_refcnt_put(block);
+
 	if (q)
 		qdisc_put(q);
 }
@@ -785,21 +796,16 @@ int tcf_block_get_ext(struct tcf_block **p_block, struct Qdisc *q,
 {
 	struct net *net = qdisc_net(q);
 	struct tcf_block *block = NULL;
-	bool created = false;
 	int err;
 
-	if (ei->block_index) {
+	if (ei->block_index)
 		/* block_index not 0 means the shared block is requested */
-		block = tcf_block_lookup(net, ei->block_index);
-		if (block)
-			refcount_inc(&block->refcnt);
-	}
+		block = tcf_block_refcnt_get(net, ei->block_index);
 
 	if (!block) {
 		block = tcf_block_create(net, q, ei->block_index, extack);
 		if (IS_ERR(block))
 			return PTR_ERR(block);
-		created = true;
 		if (tcf_block_shared(block)) {
 			err = tcf_block_insert(block, net, extack);
 			if (err)
@@ -829,14 +835,8 @@ int tcf_block_get_ext(struct tcf_block **p_block, struct Qdisc *q,
 err_chain0_head_change_cb_add:
 	tcf_block_owner_del(block, q, ei->binder_type);
 err_block_owner_add:
-	if (created) {
-		if (tcf_block_shared(block))
-			tcf_block_remove(block, net);
 err_block_insert:
-		kfree_rcu(block, rcu);
-	} else {
-		refcount_dec(&block->refcnt);
-	}
+	tcf_block_refcnt_put(block);
 	return err;
 }
 EXPORT_SYMBOL(tcf_block_get_ext);
@@ -1730,7 +1730,7 @@ static int tc_dump_tfilter(struct sk_buff *skb, struct netlink_callback *cb)
 		return err;
 
 	if (tcm->tcm_ifindex == TCM_IFINDEX_MAGIC_BLOCK) {
-		block = tcf_block_lookup(net, tcm->tcm_block_index);
+		block = tcf_block_refcnt_get(net, tcm->tcm_block_index);
 		if (!block)
 			goto out;
 		/* If we work with block index, q is NULL and parent value
@@ -1789,6 +1789,8 @@ static int tc_dump_tfilter(struct sk_buff *skb, struct netlink_callback *cb)
 		}
 	}
 
+	if (tcm->tcm_ifindex == TCM_IFINDEX_MAGIC_BLOCK)
+		tcf_block_refcnt_put(block);
 	cb->args[0] = index;
 
 out:
@@ -2055,7 +2057,7 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb)
 		return err;
 
 	if (tcm->tcm_ifindex == TCM_IFINDEX_MAGIC_BLOCK) {
-		block = tcf_block_lookup(net, tcm->tcm_block_index);
+		block = tcf_block_refcnt_get(net, tcm->tcm_block_index);
 		if (!block)
 			goto out;
 		/* If we work with block index, q is NULL and parent value
@@ -2122,6 +2124,8 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb)
 		index++;
 	}
 
+	if (tcm->tcm_ifindex == TCM_IFINDEX_MAGIC_BLOCK)
+		tcf_block_refcnt_put(block);
 	cb->args[0] = index;
 
 out: