Re: [PATCH 1/3] bridge: mrp: Add br_mrp_unique_ifindex function

[Nikolay Aleksandrov <nikolay@cumulusnetworks.com>]

On 20/05/2020 16:09, Horatiu Vultur wrote:
> It is not allow to have the same net bridge port part of multiple MRP
> rings. Therefore add a check if the port is used already in a different
> MRP. In that case return failure.
> 
> Fixes: 9a9f26e8f7ea ("bridge: mrp: Connect MRP API with the switchdev API")
> Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
> ---
>  net/bridge/br_mrp.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/net/bridge/br_mrp.c b/net/bridge/br_mrp.c
> index d7bc09de4c139..a5a3fa59c078a 100644
> --- a/net/bridge/br_mrp.c
> +++ b/net/bridge/br_mrp.c
> @@ -37,6 +37,32 @@ static struct br_mrp *br_mrp_find_id(struct net_bridge *br, u32 ring_id)
>  	return res;
>  }
>  
> +static bool br_mrp_unique_ifindex(struct net_bridge *br, u32 ifindex)
> +{
> +	struct br_mrp *mrp;
> +	bool res = true;
> +
> +	rcu_read_lock();

Why do you need the rcu_read_lock() here when lockdep_rtnl_is_held() is used?
You should be able to just do rtnl_dereference() below as this is used only
under rtnl.

> +	list_for_each_entry_rcu(mrp, &br->mrp_list, list,
> +				lockdep_rtnl_is_held()) {
> +		struct net_bridge_port *p;
> +
> +		p = rcu_dereference(mrp->p_port);
> +		if (p && p->dev->ifindex == ifindex) {
> +			res = false;
> +			break;
> +		}
> +
> +		p = rcu_dereference(mrp->s_port);
> +		if (p && p->dev->ifindex == ifindex) {
> +			res = false;
> +			break;
> +		}
> +	}
> +	rcu_read_unlock();
> +	return res;
> +}
> +
>  static struct br_mrp *br_mrp_find_port(struct net_bridge *br,
>  				       struct net_bridge_port *p)
>  {
> @@ -255,6 +281,11 @@ int br_mrp_add(struct net_bridge *br, struct br_mrp_instance *instance)
>  	    !br_mrp_get_port(br, instance->s_ifindex))
>  		return -EINVAL;
>  
> +	/* It is not possible to have the same port part of multiple rings */
> +	if (!br_mrp_unique_ifindex(br, instance->p_ifindex) ||
> +	    !br_mrp_unique_ifindex(br, instance->s_ifindex))
> +		return -EINVAL;
> +
>  	mrp = kzalloc(sizeof(*mrp), GFP_KERNEL);
>  	if (!mrp)
>  		return -ENOMEM;
>