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

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Date:   Fri, 19 May 2017 17:03:51 +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 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

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()

Ivan