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

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Date:   Fri, 19 May 2017 18:55:44 +0200
From:   Ivan Vecera <cera@...a.cz>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>,
        sashok@...ulusnetworks.com,
        Stephen Hemminger <stephen@...workplumber.org>,
        bridge@...ts.linux-foundation.org,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Subject: Re: [PATCH net] bridge: fix hello and hold timers starting/stopping

2017-05-19 18:51 GMT+02:00 Xin Long <lucien.xin@...il.com>:
> On Sat, May 20, 2017 at 12:25 AM, Ivan Vecera <cera@...a.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@...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 | 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.