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Merge branch 'net-ungraft-prio'

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Petr Machata says:

====================
When ungrafting from PRIO, replace child with FIFO

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.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2020-01-08 12:45:53 -08:00
commit 2f806c2a16
2 changed files with 15 additions and 2 deletions
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7
drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
View File

@ -651,6 +651,13 @@ mlxsw_sp_qdisc_prio_graft(struct mlxsw_sp_port *mlxsw_sp_port,
mlxsw_sp_port->tclass_qdiscs[tclass_num].handle == p->child_handle)
return 0;
if (!p->child_handle) {
/* This is an invisible FIFO replacing the original Qdisc.
* Ignore it--the original Qdisc's destroy will follow.
*/
return 0;
}
/* See if the grafted qdisc is already offloaded on any tclass. If so,
* unoffload it.
*/

10
net/sched/sch_prio.c
View File

@ -292,8 +292,14 @@ static int prio_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
struct tc_prio_qopt_offload graft_offload;
unsigned long band = arg - 1;
if (new == NULL)
new = &noop_qdisc;
if (!new) {
new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
TC_H_MAKE(sch->handle, arg), extack);
if (!new)
new = &noop_qdisc;
else
qdisc_hash_add(new, true);
}
*old = qdisc_replace(sch, new, &q->queues[band]);