net: add a noref bit on skb dst

Use low order bit of skb->_skb_dst to tell dst is not refcounted.

Change _skb_dst to _skb_refdst to make sure all uses are catched.

skb_dst() returns the dst, regardless of noref bit set or not, but
with a lockdep check to make sure a noref dst is not given if current
user is not rcu protected.

New skb_dst_set_noref() helper to set an notrefcounted dst on a skb.
(with lockdep check)

skb_dst_drop() drops a reference only if skb dst was refcounted.

skb_dst_force() helper is used to force a refcount on dst, when skb
is queued and not anymore RCU protected.

Use skb_dst_force() in __sk_add_backlog(), __dev_xmit_skb() if
!IFF_XMIT_DST_RELEASE or skb enqueued on qdisc queue, in
sock_queue_rcv_skb(), in __nf_queue().

Use skb_dst_force() in dev_requeue_skb().

Note: dst_use_noref() still dirties dst, we might transform it
later to do one dirtying per jiffies.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index a969b111bd76..a63029ef3edd 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -26,6 +26,7 @@
 #include <linux/list.h>
 #include <linux/slab.h>
 #include <net/pkt_sched.h>
+#include <net/dst.h>
 
 /* Main transmission queue. */
 
@@ -40,6 +41,7 @@
 
 static inline int dev_requeue_skb(struct sk_buff *skb, struct Qdisc *q)
 {
+        skb_dst_force(skb);
         q->gso_skb = skb;
         q->qstats.requeues++;
         q->q.qlen++;    /* it's still part of the queue */
@@ -179,7 +181,7 @@ static inline int qdisc_restart(struct Qdisc *q)
         skb = dequeue_skb(q);
         if (unlikely(!skb))
                 return 0;
-
+        WARN_ON_ONCE(skb_dst_is_noref(skb));
         root_lock = qdisc_lock(q);
         dev = qdisc_dev(q);
         txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));