Subject: [PATCH 27/39] net: sched: Fix for duplicate class dump

From: Phil Sutter <[email-masked]>
Date: Thu, 18 Oct 2018 10:34:26 +0200

[ 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 <[email-masked]>
Reviewed-by: Jiri Pirko <[email-masked]>
Reviewed-by: Eric Dumazet <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/sched/sch_api.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 99cc25aae503..57f71765febe 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -2052,7 +2052,8 @@ static int tc_dump_tclass_root(struct Qdisc *root, struct sk_buff *skb,
 
 	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;
 	}
-- 
2.19.1