From: Vladimir Oltean vladimir.oltean@nxp.com
[ Upstream commit d7d0d423dbaa73fd0506e25971dfdab6bf185d00 ]
DSA is preparing to offer switch drivers an API through which they can associate each FDB entry with a struct net_device *bridge_dev. This can be used to perform FDB isolation (the FDB lookup performed on the ingress of a standalone, or bridged port, should not find an FDB entry that is present in the FDB of another bridge).
In preparation of that work, DSA needs to ensure that by the time we call the switch .port_fdb_add and .port_fdb_del methods, the dp->bridge_dev pointer is still valid, i.e. the port is still a bridge port.
This is not guaranteed because the SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE API requires drivers that must have sleepable context to handle those events to schedule the deferred work themselves. DSA does this through the dsa_owq.
It can happen that a port leaves a bridge, del_nbp() flushes the FDB on that port, SWITCHDEV_FDB_DEL_TO_DEVICE is notified in atomic context, DSA schedules its deferred work, but del_nbp() finishes unlinking the bridge as a master from the port before DSA's deferred work is run.
Fundamentally, the port must not be unlinked from the bridge until all FDB deletion deferred work items have been flushed. The bridge must wait for the completion of these hardware accesses.
An attempt has been made to address this issue centrally in switchdev by making SWITCHDEV_FDB_DEL_TO_DEVICE deferred (=> blocking) at the switchdev level, which would offer implicit synchronization with del_nbp:
https://patchwork.kernel.org/project/netdevbpf/cover/20210820115746.3701811-...
but it seems that any attempt to modify switchdev's behavior and make the events blocking there would introduce undesirable side effects in other switchdev consumers.
The most undesirable behavior seems to be that switchdev_deferred_process_work() takes the rtnl_mutex itself, which would be worse off than having the rtnl_mutex taken individually from drivers which is what we have now (except DSA which has removed that lock since commit 0faf890fc519 ("net: dsa: drop rtnl_lock from dsa_slave_switchdev_event_work")).
So to offer the needed guarantee to DSA switch drivers, I have come up with a compromise solution that does not require switchdev rework: we already have a hook at the last moment in time when the bridge is still an upper of ours: the NETDEV_PRECHANGEUPPER handler. We can flush the dsa_owq manually from there, which makes all FDB deletions synchronous.
Signed-off-by: Vladimir Oltean vladimir.oltean@nxp.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/dsa/port.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/net/dsa/port.c b/net/dsa/port.c index 616330a16d319..3947537ed46ba 100644 --- a/net/dsa/port.c +++ b/net/dsa/port.c @@ -380,6 +380,8 @@ void dsa_port_pre_bridge_leave(struct dsa_port *dp, struct net_device *br) switchdev_bridge_port_unoffload(brport_dev, dp, &dsa_slave_switchdev_notifier, &dsa_slave_switchdev_blocking_notifier); + + dsa_flush_workqueue(); }
void dsa_port_bridge_leave(struct dsa_port *dp, struct net_device *br)