From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:in-reply-to:references:date:message-id :mime-version; bh=J5DCkWestgVKoHEZoLossBiU0LtcBuAy5pRj+r09hN4=; b=XP3vHIYmf/Ce3FGxCzpcX7HjyAZBtPpnAymzxt8qes+BDIeDOh6F7lvUPFfx9tnC2d +xpmCEvfyTHqVlt9SBLYRRGulX1GyGwjXVwLdpwO14peVNHNhC/MII2rabef1oU1ErBK uZNvN3T5485zyLUgwwpDngrc7ZKytkgjUuSjRsNTvH9Df89NPu+mu9qTsDxub0/hnh6C byCcXLsQtqiFctApMaQMfD87zErzxamzEsrJpPNHWIcIzFKIGY+PgHKumqiyb4GOareT KhMZwEFZbM0wSipJvO7WkM2n+0uetym0XUO7zrCJcc94gdFBZglaLeYg2gOGwAWC740i G1nQ== From: Hans Schultz In-Reply-To: <040a1551-2a9f-18d0-9987-f196bb429c1b@blackwall.org> References: <20220524152144.40527-1-schultz.hans+netdev@gmail.com> <20220524152144.40527-2-schultz.hans+netdev@gmail.com> <01e6e35c-f5c9-9776-1263-058f84014ed9@blackwall.org> <86zgj6oqa9.fsf@gmail.com> <86fskyggdo.fsf@gmail.com> <040a1551-2a9f-18d0-9987-f196bb429c1b@blackwall.org> Date: Wed, 25 May 2022 11:11:00 +0200 Message-ID: <86v8tu7za3.fsf@gmail.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Bridge] [PATCH V3 net-next 1/4] net: bridge: add fdb flag to extent locked port feature List-Id: Linux Ethernet Bridging List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Nikolay Aleksandrov , Hans Schultz , davem@davemloft.net, kuba@kernel.org Cc: Ivan Vecera , Andrew Lunn , Florian Fainelli , Jiri Pirko , Daniel Borkmann , netdev@vger.kernel.org, Ido Schimmel , bridge@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Eric Dumazet , linux-kselftest@vger.kernel.org, Roopa Prabhu , Paolo Abeni , Vladimir Oltean , Shuah Khan , Vivien Didelot On ons, maj 25, 2022 at 11:38, Nikolay Aleksandrov wrote: > On 25/05/2022 11:34, Hans Schultz wrote: >> On ons, maj 25, 2022 at 11:06, Nikolay Aleksandrov 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