netdev - Re: [PATCH net] net: bridge: mcast: don't delete permanent entries when fast leave is enabled

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Date:   Tue, 30 Jul 2019 20:21:06 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, roopa@...ulusnetworks.com,
        bridge@...ts.linux-foundation.org
Subject: Re: [PATCH net] net: bridge: mcast: don't delete permanent entries
 when fast leave is enabled

On 30/07/2019 20:18, David Miller wrote:
> From: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
> Date: Tue, 30 Jul 2019 14:21:00 +0300
> 
>> diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
>> index 3d8deac2353d..f8cac3702712 100644
>> --- a/net/bridge/br_multicast.c
>> +++ b/net/bridge/br_multicast.c
>> @@ -1388,6 +1388,9 @@ br_multicast_leave_group(struct net_bridge *br,
>>  			if (!br_port_group_equal(p, port, src))
>>  				continue;
>>  
>> +			if (p->flags & MDB_PG_FLAGS_PERMANENT)
>> +				break;
>> +
> 
> Like David, I also don't understand why this can be a break.  Is it because
> permanent entries are always the last on the list?  Why will there be no
> other entries that might need to be processed on the list?
> 

The reason is that only one port can match. See the first clause of br_port_group_equal,
that port can participate only once. We could easily add a break statement in the end
when a match is found and it will be correct. Even in the presence of MULTICAST_TO_UNICAST
flag, the port must match and can be added only once.