Subject: Re: [PATCH V3 net-next 1/4] net: bridge: add fdb flag to extent locked port feature

From: Hans Schultz <[email-masked]>
Date: Tue, 24 May 2022 18:21:02 +0200

>
> Hi Hans,
> So this approach has a fundamental problem, f->dst is changed without any synchronization
> you cannot rely on it and thus you cannot account for these entries properly. We must be very
> careful if we try to add any new synchronization not to affect performance as well.
> More below...
>
>> @@ -319,6 +326,9 @@ static void fdb_delete(struct net_bridge *br, struct net_bridge_fdb_entry *f,
>>  	if (test_bit(BR_FDB_STATIC, &f->flags))
>>  		fdb_del_hw_addr(br, f->key.addr.addr);
>>  
>> +	if (test_bit(BR_FDB_ENTRY_LOCKED, &f->flags) && !test_bit(BR_FDB_OFFLOADED, &f->flags))
>> +		atomic_dec(&f->dst->locked_entry_cnt);
>
> Sorry but you cannot do this for multiple reasons:
>  - f->dst can be NULL
>  - f->dst changes without any synchronization
>  - there is no synchronization between fdb's flags and its ->dst
>
> Cheers,
>  Nik

Hi Nik,

if a port is decoupled from the bridge, the locked entries would of
course be invalid, so maybe if adding and removing a port is accounted
for wrt locked entries and the count of locked entries, would that not
work?

Best,
Hans