On ons, maj 25, 2022 at 11:38, Nikolay Aleksandrov <[email protected]> wrote: > On 25/05/2022 11:34, Hans Schultz wrote: >> On ons, maj 25, 2022 at 11:06, Nikolay Aleksandrov <[email protected]> >> wrote: >>> On 24/05/2022 19:21, Hans Schultz wrote: >>>>> >>>>> 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 >>> >>> Hi Hans, >>> Unfortunately you need the correct amount of locked entries per-port if you >>> want >>> to limit their number per-port, instead of globally. So you need a >>> consistent >> >> Hi Nik, >> the used dst is a port structure, so it is per-port and not globally. >> >> Best, >> Hans >> > > Yeah, I know. :) That's why I wrote it, if the limit is not a feature > requirement I'd suggest > dropping it altogether, it can be enforced externally (e.g. from user-space) > if needed. > > By the way just fyi net-next is closed right now due to merge window. And one > more > thing please include a short log of changes between versions when you send a > new one. > I had to go look for v2 to find out what changed. >
Okay, I will drop the limit in the bridge module, which is an easy thing to do. :) (It is mostly there to ensure against DOS attacks if someone bombards a locked port with random mac addresses.) I have a similar limitation in the driver, which should then probably be dropped too? The mayor difference between v2 and v3 is in the mv88e6xxx driver, where I now keep an inventory of locked ATU entries and remove them based on a timer (mv88e6xxx_switchcore.c). I guess the mentioned log should be in the cover letter part? >>> fdb view with all its attributes when changing its dst in this case, which >>> would >>> require new locking because you have multiple dependent struct fields and >>> it will >>> kill roaming/learning scalability. I don't think this use case is worth the >>> complexity it >>> will bring, so I'd suggest an alternative - you can monitor the number of >>> locked entries >>> per-port from a user-space agent and disable port learning or some similar >>> solution that >>> doesn't require any complex kernel changes. Is the limit a requirement to >>> add the feature? >>> >>> I have an idea how to do it and to minimize the performance hit if it >>> really is needed >>> but it'll add a lot of complexity which I'd like to avoid if possible. >>> >>> Cheers, >>> Nik
