Subject: [PATCH 20/25] net_sched: fix order of queue length updates in qdisc_replace()

From: Konstantin Khlebnikov <[email-masked]>
Date: Sat, 19 Aug 2017 15:37:07 +0300

[ Upstream commit 68a66d149a8c78ec6720f268597302883e48e9fa ]

This important to call qdisc_tree_reduce_backlog() after changing queue
length. Parent qdisc should deactivate class in ->qlen_notify() called from
qdisc_tree_reduce_backlog() but this happens only if qdisc->q.qlen in zero.

Missed class deactivations leads to crashes/warnings at picking packets
from empty qdisc and corrupting state at reactivating this class in future.

Signed-off-by: Konstantin Khlebnikov <[email-masked]>
Fixes: 86a7996cc8a0 ("net_sched: introduce qdisc_replace() helper")
Acked-by: Cong Wang <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 include/net/sch_generic.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index e6aa0a249672..f18fc1a0321f 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -768,8 +768,11 @@ static inline struct Qdisc *qdisc_replace(struct Qdisc *sch, struct Qdisc *new,
 	old = *pold;
 	*pold = new;
 	if (old != NULL) {
-		qdisc_tree_reduce_backlog(old, old->q.qlen, old->qstats.backlog);
+		unsigned int qlen = old->q.qlen;
+		unsigned int backlog = old->qstats.backlog;
+
 		qdisc_reset(old);
+		qdisc_tree_reduce_backlog(old, qlen, backlog);
 	}
 	sch_tree_unlock(sch);
 
-- 
2.13.5