Messages in this thread Patch in this message | | | Date | Mon, 15 Nov 2021 20:41:36 -0500 | From | Sasha Levin <> | Subject | Re: [PATCH 5.15 301/917] net: dsa: flush switchdev workqueue when leaving the bridge |
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On Mon, Nov 15, 2021 at 11:33:59PM +0000, Vladimir Oltean wrote: >On Mon, Nov 15, 2021 at 05:56:36PM +0100, Greg Kroah-Hartman wrote: >> 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/20210820115746.3701811-1-vladimir.oltean@nxp.com/ >> >> 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) >> -- >> 2.33.0 >> >> >> > >This patch represents preparation work for a new feature. Unless it >constitutes a dependency for some other bugfix patches (which I doubt), >my suggestion is to not backport it. Thanks.
Dropped, thanks!
-- Thanks, Sasha
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