Re: [PATCH net] net: bridge: allow users setting EXT_LEARN for user FDB entries

[Nikolay Aleksandrov <razor@blackwall.org>]

On 01/09/2024 14:54, Ido Schimmel wrote:
> On Sat, Aug 31, 2024 at 11:31:50AM +0300, Nikolay Aleksandrov wrote:
>> On 30/08/2024 17:53, Jonas Gorski wrote:
>>> When userspace wants to take over a fdb entry by setting it as
>>> EXTERN_LEARNED, we set both flags BR_FDB_ADDED_BY_EXT_LEARN and
>>> BR_FDB_ADDED_BY_USER in br_fdb_external_learn_add().
>>>
>>> If the bridge updates the entry later because its port changed, we clear
>>> the BR_FDB_ADDED_BY_EXT_LEARN flag, but leave the BR_FDB_ADDED_BY_USER
>>> flag set.
>>>
>>> If userspace then wants to take over the entry again,
>>> br_fdb_external_learn_add() sees that BR_FDB_ADDED_BY_USER and skips
>>> setting the BR_FDB_ADDED_BY_EXT_LEARN flags, thus silently ignores the
>>> update:
>>>
>>>    if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
>>>            /* Refresh entry */
>>>            fdb->used = jiffies;
>>>    } else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
>>>            /* Take over SW learned entry */
>>>            set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
>>>            modified = true;
>>>    }
>>>
>>> Fix this by relaxing the condition for setting BR_FDB_ADDED_BY_EXT_LEARN
>>> by also allowing it if swdev_notify is true, which it will only be for
>>> user initiated updates.
>>>
>>> Fixes: 710ae7287737 ("net: bridge: Mark FDB entries that were added by user as such")
>>> Signed-off-by: Jonas Gorski <jonas.gorski@bisdn.de>
>>> ---
>>>  net/bridge/br_fdb.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
>>> index c77591e63841..c5d9ae13a6fb 100644
>>> --- a/net/bridge/br_fdb.c
>>> +++ b/net/bridge/br_fdb.c
>>> @@ -1472,7 +1472,8 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
>>>  		if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
>>>  			/* Refresh entry */
>>>  			fdb->used = jiffies;
>>> -		} else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
>>> +		} else if (swdev_notify ||
>>> +			   !test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
>>>  			/* Take over SW learned entry */
>>>  			set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
>>>  			modified = true;
>>
>> This literally means if added_by_user || !added_by_user, so you can probably
>> rewrite that whole block to be more straight-forward with test_and_set_bit -
>> if it was already set then refresh, if it wasn't modified = true
> 
> Hi Nik,
> 
> You mean like this [1]?
> I deleted the comment about "SW learned entry" since "extern_learn" flag
> not being set does not necessarily mean the entry was learned by SW.
> 
> [1]
> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> index c77591e63841..ad7a42b505ef 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -1469,12 +1469,10 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
>                         modified = true;
>                 }
>  
> -               if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
> +               if (test_and_set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
>                         /* Refresh entry */
>                         fdb->used = jiffies;
> -               } else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
> -                       /* Take over SW learned entry */
> -                       set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
> +               } else {
>                         modified = true;
>                 }

Yeah, that's exactly what I meant. Since the added_by_user condition becomes
redundant we can just drop it.