From: Ido Schimmel <idosch@idosch.org>
To: Vladimir Oltean <olteanv@gmail.com>
Cc: Vladimir Oltean <vladimir.oltean@nxp.com>,
netdev@vger.kernel.org, Jakub Kicinski <kuba@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Roopa Prabhu <roopa@nvidia.com>,
Nikolay Aleksandrov <nikolay@nvidia.com>,
Andrew Lunn <andrew@lunn.ch>,
Florian Fainelli <f.fainelli@gmail.com>,
Vivien Didelot <vivien.didelot@gmail.com>,
Vadym Kochan <vkochan@marvell.com>,
Taras Chornyi <tchornyi@marvell.com>,
Jiri Pirko <jiri@nvidia.com>, Ido Schimmel <idosch@nvidia.com>,
UNGLinuxDriver@microchip.com,
Grygorii Strashko <grygorii.strashko@ti.com>,
Marek Behun <kabel@blackhole.sk>,
DENG Qingfang <dqfext@gmail.com>,
Kurt Kanzenbach <kurt@linutronix.de>,
Hauke Mehrtens <hauke@hauke-m.de>,
Woojung Huh <woojung.huh@microchip.com>,
Sean Wang <sean.wang@mediatek.com>,
Landen Chao <Landen.Chao@mediatek.com>,
Claudiu Manoil <claudiu.manoil@nxp.com>,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
George McCollister <george.mccollister@gmail.com>,
Ioana Ciornei <ioana.ciornei@nxp.com>,
Saeed Mahameed <saeedm@nvidia.com>,
Leon Romanovsky <leon@kernel.org>,
Lars Povlsen <lars.povlsen@microchip.com>,
Steen Hegelund <Steen.Hegelund@microchip.com>,
Julian Wiedmann <jwi@linux.ibm.com>,
Karsten Graul <kgraul@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Ivan Vecera <ivecera@redhat.com>, Vlad Buslov <vladbu@nvidia.com>,
Jianbo Liu <jianbol@nvidia.com>, Mark Bloch <mbloch@nvidia.com>,
Roi Dayan <roid@nvidia.com>,
Tobias Waldekranz <tobias@waldekranz.com>,
Vignesh Raghavendra <vigneshr@ti.com>,
Jesse Brandeburg <jesse.brandeburg@intel.com>
Subject: Re: [PATCH v2 net-next 0/5] Make SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE blocking
Date: Fri, 20 Aug 2021 19:09:18 +0300 [thread overview]
Message-ID: <YR/TrkbhhN7QpRcQ@shredder> (raw)
In-Reply-To: <20210820093723.qdvnvdqjda3m52v6@skbuf>
On Fri, Aug 20, 2021 at 12:37:23PM +0300, Vladimir Oltean wrote:
> On Fri, Aug 20, 2021 at 12:16:10PM +0300, Ido Schimmel wrote:
> > On Thu, Aug 19, 2021 at 07:07:18PM +0300, Vladimir Oltean wrote:
> > > Problem statement:
> > >
> > > Any time a driver needs to create a private association between a bridge
> > > upper interface and use that association within its
> > > SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE handler, we have an issue with FDB
> > > entries deleted by the bridge when the port leaves. The issue is that
> > > all switchdev drivers schedule a work item to have sleepable context,
> > > and that work item can be actually scheduled after the port has left the
> > > bridge, which means the association might have already been broken by
> > > the time the scheduled FDB work item attempts to use it.
> >
> > This is handled in mlxsw by telling the device to flush the FDB entries
> > pointing to the {port, FID} when the VLAN is deleted (synchronously).
>
> Again, central solution vs mlxsw solution.
Again, a solution is forced on everyone regardless if it benefits them
or not. List is bombarded with version after version until patches are
applied. *EXHAUSTING*.
With these patches, except DSA, everyone gets another queue_work() for
each FDB entry. In some cases, it completely misses the purpose of the
patchset.
Want a central solution? Make sure it is properly integrated. "Don't
have the energy"? Ask for help. Do not try to force a solution on
everyone and motivate them to change the code by doing a poor conversion
yourself.
I don't accept "this will have to do".
>
> If a port leaves a LAG that is offloaded but the LAG does not leave the
> bridge, the driver still needs to initiate the VLAN deletion. I really
> don't like that, it makes switchdev drivers bloated.
>
> As long as you call switchdev_bridge_port_unoffload and you populate the
> blocking notifier pointer, you will get replays of item deletion from
> the bridge.
>
> > > The solution is to modify switchdev to use its embedded SWITCHDEV_F_DEFER
> > > mechanism to make the FDB notifiers emitted from the fastpath be
> > > scheduled in sleepable context. All drivers are converted to handle
> > > SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE from their blocking notifier block
> > > handler (or register a blocking switchdev notifier handler if they
> > > didn't have one). This solves the aforementioned problem because the
> > > bridge waits for the switchdev deferred work items to finish before a
> > > port leaves (del_nbp calls switchdev_deferred_process), whereas a work
> > > item privately scheduled by the driver will obviously not be waited upon
> > > by the bridge, leading to the possibility of having the race.
> >
> > How the problem is solved if after this patchset drivers still queue a
> > work item?
>
> It's only a problem if you bank on any stateful association between FDB
> entries and your ports (aka you expect that port->bridge_dev still holds
> the same value in the atomic handler as in the deferred work item). I
> think drivers don't do this at the moment, otherwise they would be
> broken.
>
> When they need that, they will convert to synchronous handling and all
> will be fine.
>
> > DSA supports learning, but does not report the entries to the bridge.
>
> Why is this relevant exactly?
Because I wanted to make sure that FDB entries that are not present in
the bridge are also flushed.
>
> > How are these entries deleted when a port leaves the bridge?
>
> dsa_port_fast_age does the following
> (a) deletes the hardware learned entries on a port, in all VLANs
> (b) notifies the bridge to also flush its software FDB on that port
>
> It is called
> (a) when the STP state changes from a learning-capable state (LEARNING,
> FORWARDING) to a non-learning capable state (BLOCKING, LISTENING)
> (b) when learning is turned off by the user
> (c) when learning is turned off by the port becoming standalone after
> leaving a bridge (actually same code path as b)
>
> So the FDB of a port is also flushed when a single switch port leaves a
> LAG that is the actual bridge port (maybe not ideal, but I don't know
> any better).
>
> > > This is a dependency for the "DSA FDB isolation" posted here. It was
> > > split out of that series hence the numbering starts directly at v2.
> > >
> > > https://patchwork.kernel.org/project/netdevbpf/cover/20210818120150.892647-1-vladimir.oltean@nxp.com/
> >
> > What is FDB isolation? Cover letter says: "There are use cases which
> > need FDB isolation between standalone ports and bridged ports, as well
> > as isolation between ports of different bridges".
>
> FDB isolation means exactly what it says: that the hardware FDB lookup
> of ports that are standalone, or under one bridge, is unable to find FDB entries
> (same MAC address, same VID) learned on another port from another bridge.
>
> > Does it mean that DSA currently forwards packets between ports even if
> > they are member in different bridges or standalone?
>
> No, that is plain forwarding isolation in my understanding of terms, and
> we have had that for many years now.
So if I have {00:01:02:03:04:05, 5} in br0, but not in br1 and now a
packet with this DMAC/VID needs to be forwarded in br1 it will be
dropped instead of being flooded?
next prev parent reply other threads:[~2021-08-20 16:09 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-19 16:07 [PATCH v2 net-next 0/5] Make SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE blocking Vladimir Oltean
2021-08-19 16:07 ` [PATCH v2 net-next 1/5] net: switchdev: move SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE to the blocking notifier chain Vladimir Oltean
2021-08-19 18:15 ` Vlad Buslov
2021-08-19 23:18 ` Vladimir Oltean
2021-08-20 7:36 ` Vlad Buslov
2021-08-19 16:07 ` [PATCH v2 net-next 2/5] net: bridge: switchdev: make br_fdb_replay offer sleepable context to consumers Vladimir Oltean
2021-08-19 16:07 ` [PATCH v2 net-next 3/5] net: switchdev: drop the atomic notifier block from switchdev_bridge_port_{,un}offload Vladimir Oltean
2021-08-19 16:07 ` [PATCH v2 net-next 4/5] net: switchdev: don't assume RCU context in switchdev_handle_fdb_{add,del}_to_device Vladimir Oltean
2021-08-19 16:07 ` [PATCH v2 net-next 5/5] net: dsa: handle SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE synchronously Vladimir Oltean
2021-08-20 9:16 ` [PATCH v2 net-next 0/5] Make SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE blocking Ido Schimmel
2021-08-20 9:37 ` Vladimir Oltean
2021-08-20 16:09 ` Ido Schimmel [this message]
2021-08-20 17:06 ` Vladimir Oltean
2021-08-20 23:36 ` Nikolay Aleksandrov
2021-08-21 0:22 ` Vladimir Oltean
2021-08-22 6:48 ` Ido Schimmel
2021-08-22 9:12 ` Nikolay Aleksandrov
2021-08-22 13:31 ` Vladimir Oltean
2021-08-22 17:06 ` Ido Schimmel
2021-08-22 17:44 ` Vladimir Oltean
2021-08-23 10:47 ` Ido Schimmel
2021-08-23 11:00 ` Vladimir Oltean
2021-08-23 12:16 ` Ido Schimmel
2021-08-23 14:29 ` Vladimir Oltean
2021-08-23 15:18 ` Ido Schimmel
2021-08-23 15:42 ` Nikolay Aleksandrov
2021-08-23 15:42 ` Vladimir Oltean
2021-08-23 16:02 ` Ido Schimmel
2021-08-23 16:11 ` Vladimir Oltean
2021-08-23 16:23 ` Vladimir Oltean
2021-08-20 10:49 ` Vladimir Oltean
2021-08-20 16:11 ` Ido Schimmel
2021-08-21 19:09 ` Vladimir Oltean
2021-08-22 7:19 ` Ido Schimmel
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