netdev - Re: [PATCH] bridge: fix bridge netlink RCU usage

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Date:	Tue, 03 Mar 2015 14:33:44 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:	Roopa Prabhu <roopa@...ulusnetworks.com>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH] bridge: fix bridge netlink RCU usage

On Tue, 2015-03-03 at 13:29 +0000, Johannes Berg wrote:

> @@ -26,12 +26,15 @@ static size_t br_get_link_af_size(const struct net_device *dev)
>  {
>         struct net_port_vlans *pv;
> 
> -       if (br_port_exists(dev))
> -               pv = nbp_get_vlan_info(br_port_get_rtnl(dev));
> -       else if (dev->priv_flags & IFF_EBRIDGE)
> +       if (br_port_exists(dev)) {
> +               rcu_read_lock();
> +               pv = nbp_get_vlan_info(br_port_get_rcu(dev));
> +               rcu_read_unlock();

Note that I'm not entirely sure about the locking for "pv" here. In this
patch I'm basically assuming that nbp_get_vlan_info() is safe in any
context, which actually seems rather unlikely.

This clearly gets rid of the lockdep complaint for me, but I'm not sure
it's actually safe.

johannes

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