netdev - Re: [PATCH net] bridge: start hello_timer when enabling KERNEL_STP in br_stp

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Date:   Fri, 19 May 2017 17:17:34 +0200
From:   Ivan Vecera <cera@...a.cz>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:     Xin Long <lucien.xin@...il.com>,
        network dev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH net] bridge: start hello_timer when enabling KERNEL_STP in br_stp_start

2017-05-19 17:05 GMT+02:00 Nikolay Aleksandrov <nikolay@...ulusnetworks.com>:
> On 5/19/17 6:03 PM, Ivan Vecera wrote:
>>
>> 2017-05-19 16:57 GMT+02:00 Nikolay Aleksandrov
>> <nikolay@...ulusnetworks.com>:
>>>
>>> On 5/19/17 5:51 PM, Ivan Vecera wrote:
>>>>
>>>>
>>>> 2017-05-19 16:45 GMT+02:00 Nikolay Aleksandrov
>>>> <nikolay@...ulusnetworks.com>:
>>>>>
>>>>>
>>>>> On 5/19/17 5:20 PM, Xin Long wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> Since commit 76b91c32dd86 ("bridge: stp: when using userspace stp stop
>>>>>> kernel hello and hold timers"), bridge would not start hello_timer if
>>>>>> stp_enabled is not KERNEL_STP when br_dev_open.
>>>>>>
>>>>>> The problem is even if users set stp_enabled with KERNEL_STP later,
>>>>>> the timer will still not be started. It causes that KERNEL_STP can
>>>>>> not really work. Users have to re-ifup the bridge to avoid this.
>>>>>>
>>>>>> This patch is to fix it by starting br->hello_timer when enabling
>>>>>> KERNEL_STP in br_stp_start.
>>>>>>
>>>>>> As an improvement, it's also to start hello_timer again only when
>>>>>> br->stp_enabled is KERNEL_STP in br_hello_timer_expired, there is
>>>>>> no reason to start the timer again when it's NO_STP.
>>>>>>
>>>>>> Fixes: 76b91c32dd86 ("bridge: stp: when using userspace stp stop
>>>>>> kernel
>>>>>> hello and hold timers")
>>>>>> Reported-by: Haidong Li <haili@...hat.com>
>>>>>> Signed-off-by: Xin Long <lucien.xin@...il.com>
>>>>>> ---
>>>>>>     net/bridge/br_stp_if.c    | 1 +
>>>>>>     net/bridge/br_stp_timer.c | 2 +-
>>>>>>     2 files changed, 2 insertions(+), 1 deletion(-)
>>>>>>
>>>>>
>>>>> This doesn't make much sense to me, how do you change from USER_STP to
>>>>> KERNEL_STP without first going through NO_STP ?
>>>>>
>>>>> If you go through NO_STP then all will be fine because br_stp_stop will
>>>>> restart
>>>>> the timers if the previous val was USER_STP.
>>>>>
>>>> The problem occurs when KERNEL_STP is enabled if the bridge itself is
>>>> already
>>>> up. Then the hello_timer is not started. If the hello and hold timers
>>>> should run only
>>>> when KERNEL_STP is used then there are another problematic places
>>>> (will send follow-up).
>>>>
>>>> Ivan
>>>>
>>>
>>> Oh, the problem seems to be rather going from NO_STP -> KERNEL_STP only
>>> then, because you cannot do direct USER_STP -> KERNEL_STP.
>>>
>> No only NO_STP->KERNEL_STP but KERNEL_STP->NO_STP as well as
>> USER_STP->NO_STP:
>>
>> 1) NO_STP->KERNEL_STP issue
>> hello_timer should be started in br_stp_start() - this patch
>>
>
> Right, I was talking only about this patch. By the way what about
> the port hold_timers ? This patch only starts the hello_timer.

The hold_timers should be started indirectly from br_transmit_config()
called from
br_config_bpdu_generation() called from hello_timer_expired() handler.

I.

>> 2) KERNEL_STP->NO_STP issue
>> hello timer and hold timers should be stopped (deleted) in br_stp_stop()
>>
>> 3) USER_STP->NO_STP issue
>> hello timer and hold timers should NOT be started in br_stp_stop()
>>
>
> Yep, ack.
>
>> Ivan
>>
>