Re: [B.A.T.M.A.N.] [PATCH 5/7] batman-adv: Make bat_priv->curr_gw an rcu protected pointer

[Marek Lindner <lindner_marek@yahoo.de>]

On Friday 04 February 2011 16:21:34 Linus Lüssing wrote:
> +	if (curr_gw) {
> +		rcu_read_unlock();
>  		return;
> +	}
> 
> -	rcu_read_lock();
>  	if (hlist_empty(&bat_priv->gw_list)) {
> -		rcu_read_unlock();
> 
> -		if (bat_priv->curr_gw) {
> +		if (curr_gw) {
> +			rcu_read_unlock();
>  			bat_dbg(DBG_BATMAN, bat_priv,
>  				"Removing selected gateway - "
>  				"no gateway in range\n");
>  			gw_deselect(bat_priv);
>  		}
> +		else
> +			rcu_read_unlock();

This is a bit odd here - we return if curr_gw is not NULL and later we print a 
message if curr_gw is not NULL ? 
The issue existed before your patch came along.


>  void gw_check_election(struct bat_priv *bat_priv, struct orig_node
> *orig_node) {
> -	struct gw_node *curr_gateway_tmp = bat_priv->curr_gw;
> +	struct gw_node *curr_gateway_tmp;
>  	uint8_t gw_tq_avg, orig_tq_avg;
> 
> +	rcu_read_lock();
> +	curr_gateway_tmp = rcu_dereference(bat_priv->curr_gw);
>  	if (!curr_gateway_tmp)
> -		return;
> +		goto rcu_unlock;
> 
>  	if (!curr_gateway_tmp->orig_node)
>  		goto deselect;

It seems if we jump to "deselect" here the rcu_lock() will never be unlocked.


> @@ -316,7 +342,7 @@ void gw_node_purge(struct bat_priv *bat_priv)
> -		if (bat_priv->curr_gw == gw_node)
> +		if (rcu_dereference(bat_priv->curr_gw) == gw_node)
>  			gw_deselect(bat_priv);

At this point we neither hold a rcu_lock() nor the newly created spinlock ...


>  	spinlock_t gw_list_lock; /* protects gw_list */
> +	spinlock_t curr_gw_lock; /* protects curr_gw updates */

Would speak anything against re-using the gw_list_lock ?

Regards,
Marek