On ons, maj 25, 2022 at 11:06, Nikolay Aleksandrov [off-list ref] wrote:

On 24/05/2022 19:21, Hans Schultz wrote:

quoted

quoted

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...

quoted

@@ -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

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