From de2d807b294d3d2ce5e59043ae2634016765d076 Mon Sep 17 00:00:00 2001 From: Maxim Mikityanskiy Date: Wed, 12 Jan 2022 12:28:05 +0200 Subject: sch_api: Don't skip qdisc attach on ingress The attach callback of struct Qdisc_ops is used by only a few qdiscs: mq, mqprio and htb. qdisc_graft() contains the following logic (pseudocode): if (!qdisc->ops->attach) { if (ingress) do ingress stuff; else do egress stuff; } if (!ingress) { ... if (qdisc->ops->attach) qdisc->ops->attach(qdisc); } else { ... } As we see, the attach callback is not called if the qdisc is being attached to ingress (TC_H_INGRESS). That wasn't a problem for mq and mqprio, since they contain a check that they are attached to TC_H_ROOT, and they can't be attached to TC_H_INGRESS anyway. However, the commit cited below added the attach callback to htb. It is needed for the hardware offload, but in the non-offload mode it simulates the "do egress stuff" part of the pseudocode above. The problem is that when htb is attached to ingress, neither "do ingress stuff" nor attach() is called. It results in an inconsistency, and the following message is printed to dmesg: unregister_netdevice: waiting for lo to become free. Usage count = 2 This commit addresses the issue by running "do ingress stuff" in the ingress flow even in the attach callback is present, which is fine, because attach isn't going to be called afterwards. The bug was found by syzbot and reported by Eric. Fixes: d03b195b5aa0 ("sch_htb: Hierarchical QoS hardware offload") Signed-off-by: Maxim Mikityanskiy Reported-by: Eric Dumazet Reviewed-by: Eric Dumazet Signed-off-by: David S. Miller --- net/sched/sch_api.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net') diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index c9c6f49f9c28..2cb496c84878 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -1062,7 +1062,7 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, qdisc_offload_graft_root(dev, new, old, extack); - if (new && new->ops->attach) + if (new && new->ops->attach && !ingress) goto skip; for (i = 0; i < num_q; i++) { -- cgit v1.2.3