net: sch_prio: When ungrafting, replace with FIFO

[ 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>

diff --git a/net/sched/sch_prio.c b/net/sched/sch_prio.c
index 18b884c..6479417 100644 (file)
--- a/net/sched/sch_prio.c
+++ b/net/sched/sch_prio.c
@@ -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]);