net_sched: fix order of queue length updates in qdisc_replace()

[ 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 <khlebnikov@yandex-team.ru>
Fixes: 86a7996cc8a0 ("net_sched: introduce qdisc_replace() helper")
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index e6aa0a2..f18fc1a 100644 (file)
--- 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);