[PATCH net 0/2] When ungrafting from PRIO, replace child with FIFO

[Petr Machata <petrm@mellanox.com>]

When a child Qdisc is removed from one of the PRIO Qdisc's bands, it is
replaced unconditionally by a NOOP qdisc. As a result, any traffic hitting
that band gets dropped. That is incorrect--no Qdisc was explicitly added
when PRIO was created, and after removal, none should have to be added
either.

In patch #2, this problem is fixed for PRIO by first attempting to create a
default Qdisc and only falling back to noop when that fails. This pattern
of attempting to create an invisible FIFO, using NOOP only as a fallback,
is also seen in some other Qdiscs.

The only driver currently offloading PRIO (and thus presumably the only one
impacted by this) is mlxsw. Therefore patch #1 extends mlxsw to handle the
replacement by an invisible FIFO gracefully.

Petr Machata (2):
  mlxsw: spectrum_qdisc: Ignore grafting of invisible FIFO
  net: sch_prio: When ungrafting, replace with FIFO

 drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c |  7 +++++++
 net/sched/sch_prio.c                                 | 10 ++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

-- 
2.20.1