[PATCH net] bridge: fix hello and hold timers starting/stopping

[PATCH net] bridge: fix hello and hold timers starting/stopping

[Ivan Vecera]

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. This is not correct as the timers are stopped in NO_STP
   case.

2. Timers are started in br_stp_stop() during USER_STP->NO_STP transition.
   This is not also correct as the timers should be stopped in NO_STP
   state.

3. Timers are NOT stopped in br_stp_stop() during KERNEL_STP->NO_STP
   transition. They should be stopped as they are running in KERNEL_STP
   state and should not run in NO_STP case.

The patch is a follow-up for "bridge: start hello_timer when enabling
KERNEL_STP in br_stp_start" patch from Xin Long.

Cc: davem@davemloft.net
Cc: sashok@cumulusnetworks.com
Cc: stephen@networkplumber.org
Cc: bridge@lists.linux-foundation.org
Cc: lucien.xin@gmail.com
Cc: nikolay@cumulusnetworks.com
Signed-off-by: Ivan Vecera <cera@cera.cz>
---
 net/bridge/br_stp_if.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index 0db8102995a5..f137ebf27755 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);
 	} else {
 		br->stp_enabled = BR_KERNEL_STP;
 		br_debug(br, "using kernel STP\n");
@@ -197,13 +191,14 @@ 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));
 		spin_lock_bh(&br->lock);
 		br_port_state_selection(br);
 		spin_unlock_bh(&br->lock);
+	} else {
+		/* BR_KERNEL_STP - stop hello and hold timers */
+		del_timer(&br->hello_timer);
+		list_for_each_entry(p, &br->port_list, list)
+			del_timer(&p->hold_timer);
 	}
 
 	br->stp_enabled = BR_NO_STP;
-- 
2.13.0

Re: [PATCH net] bridge: fix hello and hold timers starting/stopping

[Stephen Hemminger]

On Fri, 19 May 2017 18:25:43 +0200
Ivan Vecera <cera@cera.cz> 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. This is not correct as the timers are stopped in NO_STP
>    case.
> 
> 2. Timers are started in br_stp_stop() during USER_STP->NO_STP transition.
>    This is not also correct as the timers should be stopped in NO_STP
>    state.
> 
> 3. Timers are NOT stopped in br_stp_stop() during KERNEL_STP->NO_STP
>    transition. They should be stopped as they are running in KERNEL_STP
>    state and should not run in NO_STP case.
> 
> The patch is a follow-up for "bridge: start hello_timer when enabling
> KERNEL_STP in br_stp_start" patch from Xin Long.
> 
> Cc: davem@davemloft.net
> Cc: sashok@cumulusnetworks.com
> Cc: stephen@networkplumber.org
> Cc: bridge@lists.linux-foundation.org
> Cc: lucien.xin@gmail.com
> Cc: nikolay@cumulusnetworks.com
> Signed-off-by: Ivan Vecera <cera@cera.cz>

Overall, this looks correct but the wording of commit message
is too terse.

It would be better to add a more complete description of the impact
of this from a user's point of view. I am concerned that this
might have other side effects.

For example, what is the sequence of commands to validated this.

What is the impact, should this go to stable?

Re: [PATCH net] bridge: fix hello and hold timers starting/stopping

[Xin Long]

On Sat, May 20, 2017 at 12:25 AM, Ivan Vecera <cera@cera.cz> 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. This is not correct as the timers are stopped in NO_STP
>    case.
>
> 2. Timers are started in br_stp_stop() during USER_STP->NO_STP transition.
>    This is not also correct as the timers should be stopped in NO_STP
>    state.
>
> 3. Timers are NOT stopped in br_stp_stop() during KERNEL_STP->NO_STP
>    transition. They should be stopped as they are running in KERNEL_STP
>    state and should not run in NO_STP case.
>
> The patch is a follow-up for "bridge: start hello_timer when enabling
> KERNEL_STP in br_stp_start" patch from Xin Long.
>
> Cc: davem@davemloft.net
> Cc: sashok@cumulusnetworks.com
> Cc: stephen@networkplumber.org
> Cc: bridge@lists.linux-foundation.org
> Cc: lucien.xin@gmail.com
> Cc: nikolay@cumulusnetworks.com
> Signed-off-by: Ivan Vecera <cera@cera.cz>
> ---
>  net/bridge/br_stp_if.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index 0db8102995a5..f137ebf27755 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);
>         } else {
>                 br->stp_enabled = BR_KERNEL_STP;
>                 br_debug(br, "using kernel STP\n");
> @@ -197,13 +191,14 @@ 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));
>                 spin_lock_bh(&br->lock);
>                 br_port_state_selection(br);
>                 spin_unlock_bh(&br->lock);
> +       } else {
> +               /* BR_KERNEL_STP - 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 thinking, what if the timers are running when deleting them ?
del_timer may not be going to delete it, and still have to stop itself
next time when br->stp_enabled = BR_NO_STP.

So do you think it's better to do nothing here and just leave it to be
stopped by itself when checking br->stp_enabled  in
br_hello_timer_expired ?

>         }
>
>         br->stp_enabled = BR_NO_STP;
> --
> 2.13.0
>

Re: [PATCH net] bridge: fix hello and hold timers starting/stopping

[Nikolay Aleksandrov]

On 5/19/17 7:25 PM, 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. This is not correct as the timers are stopped in NO_STP
>     case.

This really is a noop, but ok.

> 
> 2. Timers are started in br_stp_stop() during USER_STP->NO_STP transition.
>     This is not also correct as the timers should be stopped in NO_STP
>     state.

Indeed, but the actual end result is almost as them being stopped because
in the timers there are specific checks if the STP == KERNEL_STP (see
br_transmit_config()) and the hold_timers will simply expire and not rearm
in any other mode. The only real problem is the hello_timer which continues
to rearm itself, but with Xin's earlier patch that is taken care of too.

> 
> 3. Timers are NOT stopped in br_stp_stop() during KERNEL_STP->NO_STP
>     transition. They should be stopped as they are running in KERNEL_STP
>     state and should not run in NO_STP case.

Same comment as for point 2.

> 
> The patch is a follow-up for "bridge: start hello_timer when enabling
> KERNEL_STP in br_stp_start" patch from Xin Long.
> 

I'd say this is more of a cleanup/improvement after Xin's patch and thus would
suggest targeting net-next. The only real issue is fixed by his patch.

> Cc: davem@davemloft.net
> Cc: sashok@cumulusnetworks.com
> Cc: stephen@networkplumber.org
> Cc: bridge@lists.linux-foundation.org
> Cc: lucien.xin@gmail.com
> Cc: nikolay@cumulusnetworks.com
> Signed-off-by: Ivan Vecera <cera@cera.cz>
> ---
>   net/bridge/br_stp_if.c | 15 +++++----------
>   1 file changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index 0db8102995a5..f137ebf27755 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);
>   	} else {
>   		br->stp_enabled = BR_KERNEL_STP;
>   		br_debug(br, "using kernel STP\n");
> @@ -197,13 +191,14 @@ 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));
>   		spin_lock_bh(&br->lock);
>   		br_port_state_selection(br);
>   		spin_unlock_bh(&br->lock);
> +	} else {
> +		/* BR_KERNEL_STP - stop hello and hold timers */
> +		del_timer(&br->hello_timer);
> +		list_for_each_entry(p, &br->port_list, list)
> +			del_timer(&p->hold_timer);
>   	}
>   
>   	br->stp_enabled = BR_NO_STP;
> 

Re: [PATCH net] bridge: fix hello and hold timers starting/stopping

[Ivan Vecera]

2017-05-19 18:51 GMT+02:00 Xin Long <lucien.xin@gmail.com>:
> On Sat, May 20, 2017 at 12:25 AM, Ivan Vecera <cera@cera.cz> 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. This is not correct as the timers are stopped in NO_STP
>>    case.
>>
>> 2. Timers are started in br_stp_stop() during USER_STP->NO_STP transition.
>>    This is not also correct as the timers should be stopped in NO_STP
>>    state.
>>
>> 3. Timers are NOT stopped in br_stp_stop() during KERNEL_STP->NO_STP
>>    transition. They should be stopped as they are running in KERNEL_STP
>>    state and should not run in NO_STP case.
>>
>> The patch is a follow-up for "bridge: start hello_timer when enabling
>> KERNEL_STP in br_stp_start" patch from Xin Long.
>>
>> Cc: davem@davemloft.net
>> Cc: sashok@cumulusnetworks.com
>> Cc: stephen@networkplumber.org
>> Cc: bridge@lists.linux-foundation.org
>> Cc: lucien.xin@gmail.com
>> Cc: nikolay@cumulusnetworks.com
>> Signed-off-by: Ivan Vecera <cera@cera.cz>
>> ---
>>  net/bridge/br_stp_if.c | 15 +++++----------
>>  1 file changed, 5 insertions(+), 10 deletions(-)
>>
>> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
>> index 0db8102995a5..f137ebf27755 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);
>>         } else {
>>                 br->stp_enabled = BR_KERNEL_STP;
>>                 br_debug(br, "using kernel STP\n");
>> @@ -197,13 +191,14 @@ 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));
>>                 spin_lock_bh(&br->lock);
>>                 br_port_state_selection(br);
>>                 spin_unlock_bh(&br->lock);
>> +       } else {
>> +               /* BR_KERNEL_STP - 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 thinking, what if the timers are running when deleting them ?
> del_timer may not be going to delete it, and still have to stop itself
> next time when br->stp_enabled = BR_NO_STP.
>
> So do you think it's better to do nothing here and just leave it to be
> stopped by itself when checking br->stp_enabled  in
> br_hello_timer_expired ?

Yes, this kind of "lazy stopping" could be safer.

I.

Re: [PATCH net] bridge: fix hello and hold timers starting/stopping

[Ivan Vecera]

2017-05-19 18:55 GMT+02:00 Nikolay Aleksandrov <nikolay@cumulusnetworks.com>:
> On 5/19/17 7:25 PM, 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. This is not correct as the timers are stopped in NO_STP
>>     case.
>
>
> This really is a noop, but ok.

Yes, stopping of stopped timers are safe but confusing.

>> 2. Timers are started in br_stp_stop() during USER_STP->NO_STP transition.
>>     This is not also correct as the timers should be stopped in NO_STP
>>     state.
>
>
> Indeed, but the actual end result is almost as them being stopped because
> in the timers there are specific checks if the STP == KERNEL_STP (see
> br_transmit_config()) and the hold_timers will simply expire and not rearm
> in any other mode. The only real problem is the hello_timer which continues
> to rearm itself, but with Xin's earlier patch that is taken care of too.

Yes, this is clean-up as well. The starting of timers are more
confusing than dangerous
but from a reader's point of view the starting of timers is non-sense
when STP is
going to be disabled.

>>
>> 3. Timers are NOT stopped in br_stp_stop() during KERNEL_STP->NO_STP
>>     transition. They should be stopped as they are running in KERNEL_STP
>>     state and should not run in NO_STP case.
>
>
> Same comment as for point 2.
This can be removed... and leave hello_timer handler to stop itself.

>> The patch is a follow-up for "bridge: start hello_timer when enabling
>> KERNEL_STP in br_stp_start" patch from Xin Long.
>>
>
> I'd say this is more of a cleanup/improvement after Xin's patch and thus
> would
> suggest targeting net-next. The only real issue is fixed by his patch.
Agree... will send resend against net-next.

Thanks for comments,
Ivan

Re: [PATCH net] bridge: fix hello and hold timers starting/stopping

[Xin Long]

On Sat, May 20, 2017 at 12:25 AM, Ivan Vecera <cera@cera.cz> wrote:
[...]
> @@ -197,13 +191,14 @@ 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));
>                 spin_lock_bh(&br->lock);
>                 br_port_state_selection(br);
>                 spin_unlock_bh(&br->lock);
> +       } else {
> +               /* BR_KERNEL_STP - stop hello and hold timers */
> +               del_timer(&br->hello_timer);
> +               list_for_each_entry(p, &br->port_list, list)
> +                       del_timer(&p->hold_timer);
>         }
>
>         br->stp_enabled = BR_NO_STP;
I have a question here, br->stp_enabled is not atomic, and it is being
changed without holding br->lock here, while it may be checked in
br_hello_timer_expired, is it safe ?

(sorry if I misunderstood or overthought about it)

> --
> 2.13.0
>