[PATCH 4.14 136/143] net: sched: Fix for duplicate class dump

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Phil Sutter <phil@xxxxxx>

[ Upstream commit 3c53ed8fef6881a864f0ee8240ed2793ef73ad0d ]

When dumping classes by parent, kernel would return classes twice:

| # tc qdisc add dev lo root prio
| # tc class show dev lo
| class prio 8001:1 parent 8001:
| class prio 8001:2 parent 8001:
| class prio 8001:3 parent 8001:
| # tc class show dev lo parent 8001:
| class prio 8001:1 parent 8001:
| class prio 8001:2 parent 8001:
| class prio 8001:3 parent 8001:
| class prio 8001:1 parent 8001:
| class prio 8001:2 parent 8001:
| class prio 8001:3 parent 8001:

This comes from qdisc_match_from_root() potentially returning the root
qdisc itself if its handle matched. Though in that case, root's classes
were already dumped a few lines above.

Fixes: cb395b2010879 ("net: sched: optimize class dumps")
Signed-off-by: Phil Sutter <phil@xxxxxx>
Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/sched/sch_api.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1917,7 +1917,8 @@ static int tc_dump_tclass_root(struct Qd
 
 	if (tcm->tcm_parent) {
 		q = qdisc_match_from_root(root, TC_H_MAJ(tcm->tcm_parent));
-		if (q && tc_dump_tclass_qdisc(q, skb, tcm, cb, t_p, s_t) < 0)
+		if (q && q != root &&
+		    tc_dump_tclass_qdisc(q, skb, tcm, cb, t_p, s_t) < 0)
 			return -1;
 		return 0;
 	}