netdev - Re: [PATCHv3] net: core: Always propagate flag changes to interfaces

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Message-ID: <528CCFC3.3050805@profihost.ag>
Date:	Wed, 20 Nov 2013 16:05:39 +0100
From:	Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>
To:	vyasevic@...hat.com, netdev@...r.kernel.org
CC:	vfalico@...hat.com
Subject: Re: [PATCHv3] net: core: Always propagate flag changes to interfaces

thanks, works fine.



Am 20.11.2013 14:54, schrieb Vlad Yasevich:
> On 11/20/2013 02:21 AM, Stefan Priebe - Profihost AG wrote:
>> Hi,
>>
>> Am 20.11.2013 02:47, schrieb Vlad Yasevich:
>>> The following commit:
>>>     b6c40d68ff6498b7f63ddf97cf0aa818d748dee7
>>>     net: only invoke dev->change_rx_flags when device is UP
>>>
>>> tried to fix a problem with VLAN devices and promiscuouse flag setting.
>>> The issue was that VLAN device was setting a flag on an interface that
>>> was down, thus resulting in bad promiscuity count.
>>> This commit blocked flag propagation to any device that is currently
>>> down.
>>>
>>> A later commit:
>>>     deede2fabe24e00bd7e246eb81cd5767dc6fcfc7
>>>     vlan: Don't propagate flag changes on down interfaces
>>>
>>> fixed VLAN code to only propagate flags when the VLAN interface is up,
>>> thus fixing the same issue as above, only localized to VLAN.
>>>
>>> The problem we have now is that if we have create a complex stack
>>> involving multiple software devices like bridges, bonds, and vlans,
>>> then it is possible that the flags would not propagate properly to
>>> the physical devices.  A simple examle of the scenario is the
>>> following:
>>>
>>>   eth0----> bond0 ----> bridge0 ---> vlan50
>>>
>>> If bond0 or eth0 happen to be down at the time bond0 is added to
>>> the bridge, then eth0 will never have promisc mode set which is
>>> currently required for operation as part of the bridge.  As a
>>> result, packets with vlan50 will be dropped by the interface.
>>>
>>> The only 2 devices that implement the special flag handling are
>>> VLAN and DSA and they both have required code to prevent incorrect
>>> flag propagation.  As a result we can remove the generic solution
>>> introduced in b6c40d68ff6498b7f63ddf97cf0aa818d748dee7 and leave
>>> it to the individual devices to decide whether they will block
>>> flag propagation or not.
>>>
>>> Reported-by: Stefan Priebe <s.priebe@...fihost.ag>
>>> Suggested-by: Veaceslav Falico <vfalico@...hat.com>
>>> Signed-off-by: Vlad Yasevich <vyasevic@...hat.com>
>>> ---
>>> v2->v3:  Removed a strange chunk that modified comments.  Not sure where it
>>>          came from.
>>>
>>>  net/core/dev.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/net/core/dev.c b/net/core/dev.c
>>> index 974143d..da9c5e1 100644
>>> --- a/net/core/dev.c
>>> +++ b/net/core/dev.c
>>> @@ -4991,7 +4991,7 @@ static void dev_change_rx_flags(struct net_device *dev, int flags)
>>>  {
>>>  	const struct net_device_ops *ops = dev->netdev_ops;
>>>  
>>> -	if ((dev->flags & IFF_UP) && ops->ndo_change_rx_flags)
>>> +	if (ops->ndo_change_rx_flags)
>>>  		ops->ndo_change_rx_flags(dev, flags);
>>>  }
>>
>> thanks for this patch - in one of the first posts you send this one:
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index fc913f4..016857b 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -4525,7 +4525,9 @@ static void dev_change_rx_flags(struct net_device
>> *dev, int flags)
>>  {
>>         const struct net_device_ops *ops = dev->netdev_ops;
>>
>> -       if ((dev->flags & IFF_UP) && ops->ndo_change_rx_flags)
>> +       if (((dev->flags & IFF_UP) ||
>> +            (dev->flags & (IFF_MASTER | IFF_SLAVE)))
>> +           && ops->ndo_change_rx_flags)
>>                 ops->ndo_change_rx_flags(dev, flags);
>>  }
>>
> 
> The new one should work just as well.  The first one I had you try
> removed the restriction for master and slave devices such as bonds
> and their slaves.  As Veaceslav pointed out, we can simply remove all
> restrictions in this code and have the individual drivers do the right
> thing.  The 2 effected drivers are VLAN and DSA and they already do the
> right checks before propagating flags.
> 
> I ran the same test with the simplified code and it worked for me
> correctly setting promisc mode in the same set-up you had:
> 
>    (phys dev) ---> bond ---->  bridge ---> vlan
> 
> -vlad
> 
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