linux-kernel - [PATCH 4.4 04/73] net: sched: do not requeue a NULL skb

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Date:	Mon, 16 May 2016 18:14:34 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Lars Persson <larper@...s.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 04/73] net: sched: do not requeue a NULL skb

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lars Persson <lars.persson@...s.com>

[ Upstream commit 3dcd493fbebfd631913df6e2773cc295d3bf7d22 ]

A failure in validate_xmit_skb_list() triggered an unconditional call
to dev_requeue_skb with skb=NULL. This slowly grows the queue
discipline's qlen count until all traffic through the queue stops.

We take the optimistic approach and continue running the queue after a
failure since it is unknown if later packets also will fail in the
validate path.

Fixes: 55a93b3ea780 ("qdisc: validate skb without holding lock")
Signed-off-by: Lars Persson <larper@...s.com>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/sched/sch_generic.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -159,12 +159,15 @@ int sch_direct_xmit(struct sk_buff *skb,
 	if (validate)
 		skb = validate_xmit_skb_list(skb, dev);
 
-	if (skb) {
+	if (likely(skb)) {
 		HARD_TX_LOCK(dev, txq, smp_processor_id());
 		if (!netif_xmit_frozen_or_stopped(txq))
 			skb = dev_hard_start_xmit(skb, dev, txq, &ret);
 
 		HARD_TX_UNLOCK(dev, txq);
+	} else {
+		spin_lock(root_lock);
+		return qdisc_qlen(q);
 	}
 	spin_lock(root_lock);