netdev - Re: [PATCH net-next v1 5/9] bonding: convert bond_has_this

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Date:	Tue, 27 Aug 2013 13:53:04 +0200
From:	Veaceslav Falico <vfalico@...hat.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	netdev@...r.kernel.org, Jay Vosburgh <fubar@...ibm.com>,
	Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH net-next v1 5/9] bonding: convert bond_has_this_ip() to
 use upper devices

On Tue, Aug 27, 2013 at 01:25:29PM +0200, Jiri Pirko wrote:
>Tue, Aug 27, 2013 at 01:16:48PM CEST, vfalico@...hat.com wrote:
>>On Mon, Aug 26, 2013 at 10:53:38PM +0200, Jiri Pirko wrote:
>>>Mon, Aug 26, 2013 at 10:32:38PM CEST, vfalico@...hat.com wrote:
>>...snip...
>>>>+	rcu_read_lock();
>>>>+	netdev_for_each_upper_dev(bond->dev, upper, iter) {
>>>>+		if (ip == bond_confirm_addr(upper, 0, ip)) {
>>>>+			ret = true;
>>>>+			break;
>>>>+		}
>>>
>>>You need the same recursion __vlan_find_dev_deep() is doing. If you do
>>>not do that, you will miss anything over the first upper level.
>>
>>Good point, and it's true for other uses also - bond_arp_send_all(), for
>>example, will also miss anything that's higher than the first upper level.
>>
>>I can't think of a use case scenario when we would need only the first
>>upper level - so maybe we should either make netdev_for_each_upper_dev()
>>recursive by default (I don't know how it can be done easily, tbh, without
>>modifying the existing code), or add something like:
>>
>>diff --git a/net/core/dev.c b/net/core/dev.c
>>index 566e99a..4a4468f 100644
>>--- a/net/core/dev.c
>>+++ b/net/core/dev.c
>>@@ -4387,6 +4387,31 @@ static void __append_search_uppers(struct list_head *search_list,
>> 	}
>> }
>>+struct net_device *netdev_upper_recursive_do_rcu(struct net_device *dev,
>>+						 struct net_device *orig_dev,
>>+						 bool (*f)(struct net_device *,
>>+							   struct net_device *))
>>+{
>>+	struct netdev_upper *upper;
>>+	struct net_device *ret = NULL;
>>+
>>+	list_for_each_entry_rcu(upper, &dev->upper_dev_list, list) {
>>+		if (f(orig_dev, upper->dev)) {
>>+			ret = upper->dev;
>>+			break;
>>+		}
>>+
>>+		if (!list_empty(&upper->dev->upper_dev_list)) {
>>+			ret = netdev_upper_recursive_do_rcu(upper->dev,
>>+							    orig_dev, f);
>>+			if (ret)
>>+				break;
>>+		}
>>+	}
>>+
>>+	return ret;
>>+}
>>+
>> static bool __netdev_search_upper_dev(struct net_device *dev,
>> 				      struct net_device *upper_dev)
>> {
>>
>>How do you think?
>
>I do not like this. How about to put all levels to upper_dev list and
>mark those who are not direct (not level1) ? Then we can use single list
>for all purposes.

I don't see how it can be done on attach/removal of upper devices, cause we
don't have a way to know the 'lower' devices, and will break scenarios like

bond -> bridge ->+ vlan

when vlan is added, we can't update bond's upper_dev_list.

And if we'll start doing it 'on the fly', while searching, by using
search_list (or something new), we'll be racy and require locking, not just
RCU.

Am I again missing something? :)
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