netdev - [net PATCH] net: sched: Fix for duplicate class dump

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Date:   Thu, 18 Oct 2018 10:34:26 +0200
From:   Phil Sutter <phil@....cc>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>
Subject: [net PATCH] net: sched: Fix for duplicate class dump

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@....cc>
---
 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 6684641ea3448..3dc0acf542454 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -2059,7 +2059,8 @@ 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;
 	}
-- 
2.19.0