netdev - Re: [patch net-next 1/2] team: use rcu_access_pointer to access RCU pointer by writer

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Date:	Wed, 20 Jun 2012 18:01:44 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, jbrouer@...hat.com,
	paulmck@...ux.vnet.ibm.com, wfg@...ux.intel.com
Subject: Re: [patch net-next 1/2] team: use rcu_access_pointer to access
 RCU pointer by writer

On Wed, 2012-06-20 at 17:32 +0200, Jiri Pirko wrote:
> Signed-off-by: Jiri Pirko <jpirko@...hat.com>
> ---
>  drivers/net/team/team_mode_activebackup.c |    7 +++++--
>  drivers/net/team/team_mode_loadbalance.c  |    8 +++++---
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/team/team_mode_activebackup.c b/drivers/net/team/team_mode_activebackup.c
> index 2fe02a8..c9e7621 100644
> --- a/drivers/net/team/team_mode_activebackup.c
> +++ b/drivers/net/team/team_mode_activebackup.c
> @@ -61,8 +61,11 @@ static void ab_port_leave(struct team *team, struct team_port *port)
>  
>  static int ab_active_port_get(struct team *team, struct team_gsetter_ctx *ctx)
>  {
> -	if (ab_priv(team)->active_port)
> -		ctx->data.u32_val = ab_priv(team)->active_port->dev->ifindex;
> +	struct team_port *active_port;
> +
> +	active_port = rcu_access_pointer(ab_priv(team)->active_port);

This is not the correct fix.

You cant safely dereference active_port if you got it from
rcu_access_pointer()

You should use rcu_dereference() of rcu_dereference_protected() or
rcu_dereference_bh() or similar variant, depending on the context.

> +	if (active_port)
> +		ctx->data.u32_val = active_port->dev->ifindex;
>  	else
>  		ctx->data.u32_val = 0;
>  	return 0;
> diff --git a/drivers/net/team/team_mode_loadbalance.c b/drivers/net/team/team_mode_loadbalance.c
> index 45cc095..b4475a5 100644
> --- a/drivers/net/team/team_mode_loadbalance.c
> +++ b/drivers/net/team/team_mode_loadbalance.c
> @@ -96,7 +96,7 @@ static void lb_tx_hash_to_port_mapping_null_port(struct team *team,
>  		struct lb_port_mapping *pm;
>  
>  		pm = &lb_priv->ex->tx_hash_to_port_mapping[i];
> -		if (pm->port == port) {
> +		if (rcu_access_pointer(pm->port) == port) {

This one is OK

>  			rcu_assign_pointer(pm->port, NULL);

I dont understand why you submit two patches...

>  			team_option_inst_set_change(pm->opt_inst_info);
>  			changed = true;
> @@ -292,7 +292,7 @@ static int lb_bpf_func_set(struct team *team, struct team_gsetter_ctx *ctx)
>  	if (lb_priv->ex->orig_fprog) {
>  		/* Clear old filter data */
>  		__fprog_destroy(lb_priv->ex->orig_fprog);
> -		sk_unattached_filter_destroy(lb_priv->fp);
> +		sk_unattached_filter_destroy(rcu_access_pointer(lb_priv->fp));
>  	}


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