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[87.243.81.1]) by smtp.gmail.com with ESMTPSA id p3-20020a1c7403000000b0039744664af7sm1749957wmc.1.2022.05.25.03.18.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 May 2022 03:18:51 -0700 (PDT) Message-ID: <4bf1c80d-0f18-f444-3005-59a45797bcfd@blackwall.org> Date: Wed, 25 May 2022 13:18:49 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH V3 net-next 1/4] net: bridge: add fdb flag to extent locked port feature Content-Language: en-US To: Hans Schultz , davem@davemloft.net, kuba@kernel.org Cc: netdev@vger.kernel.org, Andrew Lunn , Vivien Didelot , Florian Fainelli , Vladimir Oltean , Eric Dumazet , Paolo Abeni , Jiri Pirko , Ivan Vecera , Roopa Prabhu , Shuah Khan , Daniel Borkmann , Ido Schimmel , linux-kernel@vger.kernel.org, bridge@lists.linux-foundation.org, linux-kselftest@vger.kernel.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> <86v8tu7za3.fsf@gmail.com> From: Nikolay Aleksandrov In-Reply-To: <86v8tu7za3.fsf@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/05/2022 12:11, Hans Schultz wrote: > 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? > That is up to you/driver, I'd try looking for similar problems in other switch drivers and check how those were handled. There are people in the CC above that can directly answer that. :) > 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). > ack > I guess the mentioned log should be in the cover letter part? > Yep, usually a short mention of what changed to make it easier for reviewers. Some people also add the patch-specific changes to each patch under the --- so they're not included in the log, but I'm fine either way as long as I don't have to go digging up the old versions. > >>>> 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