Re: Packet gets stuck in NOLOCK pfifo_fast qdisc

[Cong Wang]

On Wed, Jul 1, 2020 at 9:05 AM Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
>
> On Tue, Jun 30, 2020 at 2:08 PM Josh Hunt <johunt@xxxxxxxxxx> wrote:
> > Do either of you know if there's been any development on a fix for this
> > issue? If not we can propose something.
>
> If you have a reproducer, I can look into this.

Does the attached patch fix this bug completely?

Thanks.
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 9092e697059e..5a03cded3054 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -123,7 +123,7 @@ bool sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
 
 void __qdisc_run(struct Qdisc *q);
 
-static inline void qdisc_run(struct Qdisc *q)
+static inline bool qdisc_run(struct Qdisc *q)
 {
 	if (qdisc_run_begin(q)) {
 		/* NOLOCK qdisc must check 'state' under the qdisc seqlock
@@ -133,7 +133,9 @@ static inline void qdisc_run(struct Qdisc *q)
 		    likely(!test_bit(__QDISC_STATE_DEACTIVATED, &q->state)))
 			__qdisc_run(q);
 		qdisc_run_end(q);
+		return true;
 	}
+	return false;
 }
 
 static inline __be16 tc_skb_protocol(const struct sk_buff *skb)
diff --git a/net/core/dev.c b/net/core/dev.c
index 90b59fc50dc9..c7e48356132a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3744,7 +3744,8 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
 
 	if (q->flags & TCQ_F_NOLOCK) {
 		rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
-		qdisc_run(q);
+		if (!qdisc_run(q) && rc == NET_XMIT_SUCCESS)
+			__netif_schedule(q);
 
 		if (unlikely(to_free))
 			kfree_skb_list(to_free);