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

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Date:   Fri, 19 May 2017 17:57:42 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     ivan.vecera@...a.cz
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

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.