netdev - Re: [PATCH net-next v2] bridge: fix hello and hold timers starting/stopping

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Date:   Sat, 20 May 2017 09:55:14 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Hangbin Liu <liuhangbin@...il.com>, Ivan Vecera <cera@...a.cz>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        sashok@...ulusnetworks.com, stephen@...workplumber.org,
        bridge@...ts.linux-foundation.org, lucien.xin@...il.com
Subject: Re: [PATCH net-next v2] bridge: fix hello and hold timers
 starting/stopping

On 5/20/17 8:57 AM, Hangbin Liu wrote:
> On Fri, May 19, 2017 at 07:30:43PM +0200, Ivan Vecera wrote:
>> Current bridge code incorrectly handles starting/stopping of hello and
>> hold timers during STP enable/disable.
>>
>> 1. Timers are stopped in br_stp_start() during NO_STP->USER_STP
>>     transition. The timers are already stopped in NO_STP state so
>>     this is confusing no-op.
> 
> Hi Ivan,
> 
> Shouldn't we start hello timer in br_stp_start when NO_STP -> BR_KERNEL_STP ?

Please see Xin Long's recent -net patch that fixes exactly this issue.
It will answer your questions below, too.

https://patchwork.ozlabs.org/patch/764685/

>>
>> 2. During USER_STP->NO_STP transition the timers are started. This
>>     does not make sense and is confusion because the timer should not be
>>     active in NO_STP state.
> 
> Yes, but what about BR_KERNEL_STP -> NO_STP in function br_stp_stop() ?
>>
>> Cc: davem@...emloft.net
>> Cc: sashok@...ulusnetworks.com
>> Cc: stephen@...workplumber.org
>> Cc: bridge@...ts.linux-foundation.org
>> Cc: lucien.xin@...il.com
>> Cc: nikolay@...ulusnetworks.com
>> Signed-off-by: Ivan Vecera <cera@...a.cz>
>> ---
>>   net/bridge/br_stp_if.c | 11 -----------
>>   1 file changed, 11 deletions(-)
>>
>> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
>> index 08341d2aa9c9..a05027027513 100644
>> --- a/net/bridge/br_stp_if.c
>> +++ b/net/bridge/br_stp_if.c
>> @@ -150,7 +150,6 @@ static int br_stp_call_user(struct net_bridge *br, char *arg)
>>   
>>   static void br_stp_start(struct net_bridge *br)
>>   {
>> -	struct net_bridge_port *p;
>>   	int err = -ENOENT;
>>   
>>   	if (net_eq(dev_net(br->dev), &init_net))
>> @@ -169,11 +168,6 @@ static void br_stp_start(struct net_bridge *br)
>>   	if (!err) {
>>   		br->stp_enabled = BR_USER_STP;
>>   		br_debug(br, "userspace STP started\n");
>> -
>> -		/* Stop hello and hold timers */
>> -		del_timer(&br->hello_timer);
>> -		list_for_each_entry(p, &br->port_list, list)
>> -			del_timer(&p->hold_timer);
> 
> I'm not sure if user space daemon will send bpdu or not? In comment
> 76b91c32dd86 ("bridge: stp: when using userspace stp stop kernel hello and
> hold timers"). Nikolay said we should not handle it with BR_USER_STP >
>>   	} else {
>>   		br->stp_enabled = BR_KERNEL_STP;
>>   		br_debug(br, "using kernel STP\n");
>> @@ -187,7 +181,6 @@ static void br_stp_start(struct net_bridge *br)
>>   
>>   static void br_stp_stop(struct net_bridge *br)
>>   {
>> -	struct net_bridge_port *p;
>>   	int err;
>>   
>>   	if (br->stp_enabled == BR_USER_STP) {
>> @@ -196,10 +189,6 @@ static void br_stp_stop(struct net_bridge *br)
>>   			br_err(br, "failed to stop userspace STP (%d)\n", err);
>>   
>>   		/* To start timers on any ports left in blocking */
>> -		mod_timer(&br->hello_timer, jiffies + br->hello_time);
>> -		list_for_each_entry(p, &br->port_list, list)
>> -			mod_timer(&p->hold_timer,
>> -				  round_jiffies(jiffies + BR_HOLD_TIME));
> 
> If we do not del hello_timer. after it expired in br_hello_timer_expired(),
> Our state is br->dev->flags & IFF_UP and br->stp_enabled == NO_STP, it will
> call mod_timer(&br->hello_timer, round_jiffies(jiffies + br->hello_time))
> and we will keep sending bpdu message even after stp stoped.

Again see Xin Long's recent -net patch.

> 
>>   		spin_lock_bh(&br->lock);
>>   		br_port_state_selection(br);
>>   		spin_unlock_bh(&br->lock);
>> -- 
> 
> So how about just like
> 
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index d8ad73b..0198f62 100644
> --- a/net/bridge/br_stp_if.c
> +++ b/net/bridge/br_stp_if.c
> @@ -183,6 +183,7 @@ static void br_stp_start(struct net_bridge *br)
>          } else {
>                  br->stp_enabled = BR_KERNEL_STP;
>                  br_debug(br, "using kernel STP\n");
> +               mod_timer(&br->hello_timer, jiffies + br->hello_time);
> 
>                  /* To start timers on any ports left in blocking */
>                  br_port_state_selection(br);
> @@ -202,7 +203,6 @@ static void br_stp_stop(struct net_bridge *br)
>                          br_err(br, "failed to stop userspace STP (%d)\n", err);
> 
>                  /* To start timers on any ports left in blocking */
> -               mod_timer(&br->hello_timer, jiffies + br->hello_time);
>                  list_for_each_entry(p, &br->port_list, list)
>                          mod_timer(&p->hold_timer,
>                                    round_jiffies(jiffies + BR_HOLD_TIME));
> @@ -211,6 +211,7 @@ static void br_stp_stop(struct net_bridge *br)
>                  spin_unlock_bh(&br->lock);
>          }
> 
> +       del_timer_sync(&br->hello_timer);
>          br->stp_enabled = BR_NO_STP;
>   }
> 
> Thanks
> Hangbin
>