net: sched: refactor tcf_block_find() into standalone functions

Refactor tcf_block_find() code into three standalone functions:
- __tcf_qdisc_find() to lookup Qdisc and increment its reference counter.
- __tcf_qdisc_cl_find() to lookup class.
- __tcf_block_find() to lookup block and increment its reference counter.

This change is necessary to allow netlink tc rule update handlers to call
these functions directly in order to conditionally take rtnl lock
according to Qdisc class ops flags before calling any of class ops
functions.
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

@@ -1101,6 +1101,142 @@ static void tcf_block_flush_all_chains(struct tcf_block *block, bool rtnl_held)
 	}
 }
 
+/* Lookup Qdisc and increments its reference counter.
+ * Set parent, if necessary.
+ */
+
+static int __tcf_qdisc_find(struct net *net, struct Qdisc **q,
+			    u32 *parent, int ifindex, bool rtnl_held,
+			    struct netlink_ext_ack *extack)
+{
+	const struct Qdisc_class_ops *cops;
+	struct net_device *dev;
+	int err = 0;
+
+	if (ifindex == TCM_IFINDEX_MAGIC_BLOCK)
+		return 0;
+
+	rcu_read_lock();
+
+	/* Find link */
+	dev = dev_get_by_index_rcu(net, ifindex);
+	if (!dev) {
+		rcu_read_unlock();
+		return -ENODEV;
+	}
+
+	/* Find qdisc */
+	if (!*parent) {
+		*q = dev->qdisc;
+		*parent = (*q)->handle;
+	} else {
+		*q = qdisc_lookup_rcu(dev, TC_H_MAJ(*parent));
+		if (!*q) {
+			NL_SET_ERR_MSG(extack, "Parent Qdisc doesn't exists");
+			err = -EINVAL;
+			goto errout_rcu;
+		}
+	}
+
+	*q = qdisc_refcount_inc_nz(*q);
+	if (!*q) {
+		NL_SET_ERR_MSG(extack, "Parent Qdisc doesn't exists");
+		err = -EINVAL;
+		goto errout_rcu;
+	}
+
+	/* Is it classful? */
+	cops = (*q)->ops->cl_ops;
+	if (!cops) {
+		NL_SET_ERR_MSG(extack, "Qdisc not classful");
+		err = -EINVAL;
+		goto errout_qdisc;
+	}
+
+	if (!cops->tcf_block) {
+		NL_SET_ERR_MSG(extack, "Class doesn't support blocks");
+		err = -EOPNOTSUPP;
+		goto errout_qdisc;
+	}
+
+errout_rcu:
+	/* At this point we know that qdisc is not noop_qdisc,
+	 * which means that qdisc holds a reference to net_device
+	 * and we hold a reference to qdisc, so it is safe to release
+	 * rcu read lock.
+	 */
+	rcu_read_unlock();
+	return err;
+
+errout_qdisc:
+	rcu_read_unlock();
+
+	if (rtnl_held)
+		qdisc_put(*q);
+	else
+		qdisc_put_unlocked(*q);
+	*q = NULL;
+
+	return err;
+}
+
+static int __tcf_qdisc_cl_find(struct Qdisc *q, u32 parent, unsigned long *cl,
+			       int ifindex, struct netlink_ext_ack *extack)
+{
+	if (ifindex == TCM_IFINDEX_MAGIC_BLOCK)
+		return 0;
+
+	/* Do we search for filter, attached to class? */
+	if (TC_H_MIN(parent)) {
+		const struct Qdisc_class_ops *cops = q->ops->cl_ops;
+
+		*cl = cops->find(q, parent);
+		if (*cl == 0) {
+			NL_SET_ERR_MSG(extack, "Specified class doesn't exist");
+			return -ENOENT;
+		}
+	}
+
+	return 0;
+}
+
+static struct tcf_block *__tcf_block_find(struct net *net, struct Qdisc *q,
+					  unsigned long cl, int ifindex,
+					  u32 block_index,
+					  struct netlink_ext_ack *extack)
+{
+	struct tcf_block *block;
+
+	if (ifindex == TCM_IFINDEX_MAGIC_BLOCK) {
+		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);
+		}
+	} else {
+		const struct Qdisc_class_ops *cops = q->ops->cl_ops;
+
+		block = cops->tcf_block(q, cl, extack);
+		if (!block)
+			return ERR_PTR(-EINVAL);
+
+		if (tcf_block_shared(block)) {
+			NL_SET_ERR_MSG(extack, "This filter block is shared. Please use the block index to manipulate the filters");
+			return ERR_PTR(-EOPNOTSUPP);
+		}
+
+		/* 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;
+}
+
 static void __tcf_block_put(struct tcf_block *block, struct Qdisc *q,
 			    struct tcf_block_ext_info *ei, bool rtnl_held)
 {
@@ -1146,106 +1282,27 @@ static struct tcf_block *tcf_block_find(struct net *net, struct Qdisc **q,
 	struct tcf_block *block;
 	int err = 0;
 
-	if (ifindex == TCM_IFINDEX_MAGIC_BLOCK) {
-		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);
-		}
-	} else {
-		const struct Qdisc_class_ops *cops;
-		struct net_device *dev;
-
-		rcu_read_lock();
-
-		/* Find link */
-		dev = dev_get_by_index_rcu(net, ifindex);
-		if (!dev) {
-			rcu_read_unlock();
-			return ERR_PTR(-ENODEV);
-		}
-
-		/* Find qdisc */
-		if (!*parent) {
-			*q = dev->qdisc;
-			*parent = (*q)->handle;
-		} else {
-			*q = qdisc_lookup_rcu(dev, TC_H_MAJ(*parent));
-			if (!*q) {
-				NL_SET_ERR_MSG(extack, "Parent Qdisc doesn't exists");
-				err = -EINVAL;
-				goto errout_rcu;
-			}
-		}
-
-		*q = qdisc_refcount_inc_nz(*q);
-		if (!*q) {
-			NL_SET_ERR_MSG(extack, "Parent Qdisc doesn't exists");
-			err = -EINVAL;
-			goto errout_rcu;
-		}
-
-		/* Is it classful? */
-		cops = (*q)->ops->cl_ops;
-		if (!cops) {
-			NL_SET_ERR_MSG(extack, "Qdisc not classful");
-			err = -EINVAL;
-			goto errout_rcu;
-		}
-
-		if (!cops->tcf_block) {
-			NL_SET_ERR_MSG(extack, "Class doesn't support blocks");
-			err = -EOPNOTSUPP;
-			goto errout_rcu;
-		}
-
-		/* At this point we know that qdisc is not noop_qdisc,
-		 * which means that qdisc holds a reference to net_device
-		 * and we hold a reference to qdisc, so it is safe to release
-		 * rcu read lock.
-		 */
-		rcu_read_unlock();
+	ASSERT_RTNL();
 
-		/* Do we search for filter, attached to class? */
-		if (TC_H_MIN(*parent)) {
-			*cl = cops->find(*q, *parent);
-			if (*cl == 0) {
-				NL_SET_ERR_MSG(extack, "Specified class doesn't exist");
-				err = -ENOENT;
-				goto errout_qdisc;
-			}
-		}
+	err = __tcf_qdisc_find(net, q, parent, ifindex, true, extack);
+	if (err)
+		goto errout;
 
-		/* And the last stroke */
-		block = cops->tcf_block(*q, *cl, extack);
-		if (!block) {
-			err = -EINVAL;
-			goto errout_qdisc;
-		}
-		if (tcf_block_shared(block)) {
-			NL_SET_ERR_MSG(extack, "This filter block is shared. Please use the block index to manipulate the filters");
-			err = -EOPNOTSUPP;
-			goto errout_qdisc;
-		}
+	err = __tcf_qdisc_cl_find(*q, *parent, cl, ifindex, extack);
+	if (err)
+		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);
-	}
+	block = __tcf_block_find(net, *q, *cl, ifindex, block_index, extack);
+	if (IS_ERR(block))
+		goto errout_qdisc;
 
 	return block;
 
-errout_rcu:
-	rcu_read_unlock();
 errout_qdisc:
-	if (*q) {
+	if (*q)
 		qdisc_put(*q);
-		*q = NULL;
-	}
+errout:
+	*q = NULL;
 	return ERR_PTR(err);
 }