netdev - Re: Regression: net/ipv6/mld running system out of memory (not a leak)

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Date:   Tue, 3 Mar 2020 17:11:05 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Rafał Miłecki <zajec5@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Jo-Philipp Wich <jo@...n.io>
Subject: Re: Regression: net/ipv6/mld running system out of memory (not a
 leak)

On Tue, Mar 03, 2020 at 05:00:35PM +0800, Hangbin Liu wrote:
> On Tue, Mar 03, 2020 at 07:16:44AM +0100, Rafał Miłecki wrote:
> > It appears that every interface up & down sequence results in adding a
> > new ff02::2 entry to the idev->mc_tomb. Doing that over and over will
> > obviously result in running out of memory at some point. That list isn't
> > cleared until removing an interface.
> 
> Thanks Rafał, this info is very useful. When we set interface up, we will
> call ipv6_add_dev() and add in6addr_linklocal_allrouters to the mcast list.
> But we only remove it in ipv6_mc_destroy_dev(). This make the link down save
> the list and link up add a new one.
> 
> Maybe we should remove the list in ipv6_mc_down(). like:

Or maybe we just remove the list in addrconf_ifdown(), as opposite of
ipv6_add_dev(), which looks more clear.

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 164c71c54b5c..4369087b8b74 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3841,6 +3841,12 @@ static int addrconf_ifdown(struct net_device *dev, int how)
                ipv6_ac_destroy_dev(idev);
                ipv6_mc_destroy_dev(idev);
        } else {
+               ipv6_dev_mc_dec(dev, &in6addr_interfacelocal_allnodes);
+               ipv6_dev_mc_dec(dev, &in6addr_linklocal_allnodes);
+
+               if (idev->cnf.forwarding && (dev->flags & IFF_MULTICAST))
+                       ipv6_dev_mc_dec(dev, &in6addr_linklocal_allrouters);
+
                ipv6_mc_down(idev);
        }

Thanks
Hangbin