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 20:33:59 +0200
From:	Jiri Pirko <jpirko@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.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

Wed, Jun 20, 2012 at 06:01:44PM CEST, eric.dumazet@...il.com wrote:
>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.


Okay, reworking this using rcu_dereference_protected() since this is
update path.

>
>> +	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...

Squashing into one now.

>
>>  			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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