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Subject[PATCH 4.14 61/62] net: sch_prio: When ungrafting, replace with FIFO
Date
From: Petr Machata <petrm@mellanox.com>

[ Upstream commit 240ce7f6428ff5188b9eedc066e1e4d645b8635f ]

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: 1da177e4c3f4 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/sch_prio.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

--- a/net/sched/sch_prio.c
+++ b/net/sched/sch_prio.c
@@ -244,8 +244,14 @@ static int prio_graft(struct Qdisc *sch,
struct prio_sched_data *q = qdisc_priv(sch);
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));
+ if (!new)
+ new = &noop_qdisc;
+ else
+ qdisc_hash_add(new, true);
+ }

*old = qdisc_replace(sch, new, &q->queues[band]);
return 0;

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