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

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 protected]> Fixes: 86a7996 ("net_sched: introduce qdisc_replace() helper") Acked-by: Cong Wang <[email protected]> Signed-off-by: David S. Miller <[email protected]>
ambv · Aug 21, 2017 · 68a66d1 · 68a66d1
1 parent 49bf4b3
commit 68a66d1
Showing 1 changed file with 4 additions and 1 deletion.
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
@@ -806,8 +806,11 @@ 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);