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

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Date:   Fri, 19 May 2017 16:51:55 +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 16:45 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