netdev - Re: [PATCH net] bridge: a netlink notification should be sent whenever those attributes change

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Date:	Sat, 5 Mar 2016 20:43:07 +0100
From:	Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:	Xin Long <lucien.xin@...il.com>
Cc:	network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net] bridge: a netlink notification should be sent
 whenever those attributes change

On 03/05/2016 03:44 PM, Xin Long wrote:
> On Thu, Mar 3, 2016 at 8:29 PM, Nikolay Aleksandrov
> <nikolay@...ulusnetworks.com> wrote:
>>
>> This is incorrect because you don't have rtnl here, bridge device sysfs
>> options take care of rtnl only on per-option basis and they obtain and
>> release it themselves, so you won't have rtnl held when you call
>> netdev_state_change. While I agree that this is needed, a larger change
>> would be necessary for br_sysfs_br.c.
> Sorry, I can't follow you, cause I didn't see any held in dev_ioctl, like:
> ipip6_tunnel_ioctl
>     ipip6_tunnel_update
>         netdev_state_change
> 
> why sysfs have to hold rtnl ?
> 

See the comment above dev_ifsioc:
/*
 *      Perform the SIOCxIFxxx calls, inside rtnl_lock()
 */
static int dev_ifsioc(struct net *net, struct ifreq *ifr, unsigned int cmd)
{
...
it is usually called like:
                       rtnl_lock();
                       ret = dev_ifsioc(net, &ifr, cmd);
                       rtnl_unlock();
And also you cannot be calling netdevice notifiers without RTNL. So in any
case you do need it here as well, in fact you'll surely hit the ASSERT_RTNL();
in call_netdevice_notifiers_info if you do so, thus I'm not sure how this
patch was actually tested.

>> Off-topic: I've been looking into factoring out the bond option API and reusing
>> it here as it already has all of this handled, but I won't have time to finish
>> it before the next merge window, so if you fix the issue here I'm okay with
>> this as interim solution.
>>
>> Cheers,
>>  Nik
>>