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

["Rafał Miłecki" <zajec5@gmail.com>]

On 04.03.2020 07:45, Hangbin Liu wrote:
> On Tue, Mar 03, 2020 at 10:23:12AM +0100, Rafał Miłecki wrote:
>> On 03.03.2020 10:11, Hangbin Liu wrote:
>>> 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);
>>>           }
>>
>> FWIW I can confirm it fixes the problem for me!
>>
>> Only one ff02::2 entry is present when removing interface:
>>
>> [  105.686503] [ipv6_mc_destroy_dev] idev->dev->name:mon-phy0
>> [  105.692056] [ipv6_mc_down] idev->dev->name:mon-phy0
>> [  105.696957] [ipv6_mc_destroy_dev -> __mld_clear_delrec] kfree(pmc:c64fd880) ff02::2
> 
> Hi Rafał,
> 
> When review the code, I got confused. On the latest net code, we only
> add the allrouter address to multicast list in function
> 1) ipv6_add_dev(), which only called when there is no idev. But link down and
>     up would not re-create idev.
> 2) dev_forward_change(), which only be called during forward change, this
>     function will handle add/remove allrouter address correctly.

Sharp eye! You're right, I tracked (with just a pr_info) all usages of
in6addr_linklocal_allrouters and none gets triggered during my testing
routine. I'm wondering if I should start blaming my OpenWrt user space
now.


> So I still don't know how you could added the ff02::2 on same dev multi times.
> Does just do `ip link set $dev down; ip link set $dev up` reproduce your
> problem? Or did I miss something?

A bit old-fashioned with ifconfig but basically yes, that's my test:

iw phy phy0 interface add mon-phy0 type monitor
for i in $(seq 1 10); do ifconfig mon-phy0 up; ifconfig mon-phy0 down; done
iw dev mon-phy0 del