Subject: Re: [IFGROUPv4 2/3] Interface group: core (netlink) part

From: Patrick McHardy <[email-masked]>
Date: Thu, 25 Oct 2007 17:40:57 +0200

Laszlo Attila Toth wrote:
> Patrick McHardy írta:
>> Laszlo Attila Toth wrote:
>>> Interface groups let handle different interfaces together
>>> especially in netfilter modules.
>>> Modified net device structure and netlink interface.
>>>
>>> @@ -891,6 +895,13 @@ static int do_setlink(struct net_device *dev, 
>>> struct ifinfomsg *ifm,
>>>          }
>>>      }
>>>  
>>> +    if (tb[IFLA_IFGROUP]) {
>>> +        write_lock_bh(&dev_base_lock);
>>> +        dev->ifgroup = nla_get_u32(tb[IFLA_IFGROUP]);
>>> +        write_unlock_bh(&dev_base_lock);
>>> +        modified = 1;
>>> +    }
>>
>>
>> The locking looks unnecessary, the rtnl should be enough.
>> I'm not even sure why its used for operstate and linkmode,
>> AFAICS they are also protected by the rtnl.
>>
> 
> Hm, ok. In this case operstate and linkmode can be unprotected as code 
> cleanup, am I right? Or leave them unchanged?

There seems to be a single case where operstate is used without
the rtnl (under dev_base_lock), in dev_get_flags() invoked by
dev_ifsioc_locked(). But that looks like a bug, there are many
callers of dev_change_flags() that only take the rtnl. So this
would be more a fix than a cleanup.

> And notification is only needed if something was changed.

Yes.