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net: sch_prio: When ungrafting, replace 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.

Fix 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 other
Qdiscs.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Petr Machata <petrm@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Petr Machata 2020-01-06 18:01:56 +00:00 committed by David S. Miller
parent 3971a535b8
commit 240ce7f642
1 changed files with 8 additions and 2 deletions
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8
net/sched/sch_prio.c
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@ -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)
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]);