Patch "net_sched: fix order of queue length updates in qdisc_replace()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net_sched-fix-order-of-queue-length-updates-in-qdisc_replace.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Konstantin Khlebnikov <[email protected]>
Date: Sat, 19 Aug 2017 15:37:07 +0300
Subject: net_sched: fix order of queue length updates in qdisc_replace()

From: Konstantin Khlebnikov <[email protected]>

[ 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.

---
 include/net/sch_generic.h |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

@@ -768,8 +768,11 @@ static inline struct Qdisc *qdisc_replac
 	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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/net_sched-remove-warning-from-qdisc_hash_add.patch queue-4.9/net_sched-fix-order-of-queue-length-updates-in-qdisc_replace.patch queue-4.9/net_sched-sfq-update-hierarchical-backlog-when-drop-packet.patch