[PATCH 4.5 005/101] net: sched: do not requeue a NULL skb

Greg Kroah-Hartman
2016-05-17T01:26:25Z

From: Lars Persson <lars.persson@axis.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@axis.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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);