[v4,net,0/2] net: bridge: switchdev: Ensure MDB events are delivered exactly once

Message

Tobias Waldekranz Feb. 12, 2024, 7:18 p.m. UTC

When a device is attached to a bridge, drivers will request a replay
of objects that were created before the device joined the bridge, that
are still of interest to the joining port. Typical examples include
FDB entries and MDB memberships on other ports ("foreign interfaces")
or on the bridge itself.

Conversely when a device is detached, the bridge will synthesize
deletion events for all those objects that are still live, but no
longer applicable to the device in question.

This series eliminates two races related to the synching and
unsynching phases of a bridge's MDB with a joining or leaving device,
that would cause notifications of such objects to be either delivered
twice (1/2), or not at all (2/2).

A similar race to the one solved by 1/2 still remains for the
FDB. This is much harder to solve, due to the lockless operation of
the FDB's rhashtable, and is therefore knowingly left out of this
series.

v1 -> v2:
- Squash the previously separate addition of
  switchdev_port_obj_act_is_deferred into first consumer.
- Use ether_addr_equal to compare MAC addresses.
- Document switchdev_port_obj_act_is_deferred (renamed from
  switchdev_port_obj_is_deferred in v1, to indicate that we also match
  on the action).
- Delay allocations of MDB objects until we know they're needed.
- Use non-RCU version of the hash list iterator, now that the MDB is
  not scanned while holding the RCU read lock.
- Add Fixes tag to commit message

v2 -> v3:
- Fix unlocking in error paths
- Access RCU protected port list via mlock_dereference, since MDB is
  guaranteed to remain constant for the duration of the scan.

v3 -> v4:
- Limit the search for exiting deferred events in 1/2 to only apply to
  additions, since the problem does not exist in the deletion case.
- Add 2/2, to plug a related race when unoffloading an indirectly
  associated device.

Tobias Waldekranz (2):
  net: bridge: switchdev: Skip MDB replays of deferred events on offload
  net: bridge: switchdev: Ensure deferred event delivery on unoffload

 include/net/switchdev.h   |  3 ++
 net/bridge/br_switchdev.c | 84 ++++++++++++++++++++++++++-------------
 net/switchdev/switchdev.c | 73 ++++++++++++++++++++++++++++++++++
 3 files changed, 132 insertions(+), 28 deletions(-)