From: Neil Horman <nhorman@redhat.com>
Date: Thu, 24 Jul 2008 15:17:48 -0400
Subject: [net] proc: add unresolved discards stat to ndisc_cache
Message-id: 20080724191748.GC17344@hmsendeavour.rdu.redhat.com
O-Subject: [RHEL 5.3 PATCH] net: add unresolved discards stat to /proc/net/stat/ndisc_cache (bz 453173)
Bugzilla: 456732
RH-Acked-by: David S. Miller <davem@redhat.com>

Hey-
	We recently had a problem at NYSE in which frames were periodically
getting retransmitted on a tcp stream.  In attempting to track down where the
frame was getting dropped, we discovered that the frame was lost internally to
the network stack, but no drop counter was getting incremented in response to
it.  Careful auditing by several people eventually revealed that we could drop
in the neighbor cache if frames were being sent to a neighbor with an incomplete
entry (the arp_queue list that skb are enqueued to during resolution is limited
to 3 skbs by default).  This patch is a backport of commit
9a6d276e85aa3d8f308fc5e8de6892daeb60ae5f in DaveM's net-next tree to add an
unresolved discards counter to the ndisc_cache proc file, so that frames lost
here in the future will be visible.  Satisfies bz 453173

Neil

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 4901ee4..62f832b 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -99,7 +99,7 @@ struct neigh_statistics
 	unsigned long destroys;		/* number of destroyed neighs */
 	unsigned long hash_grows;	/* number of hash resizes */
 
-	unsigned long res_failed;	/* nomber of failed resolutions */
+	unsigned long res_failed;	/* number of failed resolutions */
 
 	unsigned long lookups;		/* number of lookups */
 	unsigned long hits;		/* number of hits (among lookups) */
@@ -109,6 +109,9 @@ struct neigh_statistics
 
 	unsigned long periodic_gc_runs;	/* number of periodic GC runs */
 	unsigned long forced_gc_runs;	/* number of forced GC runs */
+#ifndef __GENKSYMS__
+	unsigned long unres_discards;	/* number of unresolved drops */
+#endif
 };
 
 #define NEIGH_CACHE_STAT_INC(tbl, field)				\
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index fe2113f..f76696e 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -878,6 +878,7 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
 				buff = neigh->arp_queue.next;
 				__skb_unlink(buff, &neigh->arp_queue);
 				kfree_skb(buff);
+				NEIGH_CACHE_STAT_INC(neigh->tbl, unres_discards);
 			}
 			__skb_queue_tail(&neigh->arp_queue, skb);
 		}
@@ -2282,12 +2283,12 @@ static int neigh_stat_seq_show(struct seq_file *seq, void *v)
 	struct neigh_statistics *st = v;
 
 	if (v == SEQ_START_TOKEN) {
-		seq_printf(seq, "entries  allocs destroys hash_grows  lookups hits  res_failed  rcv_probes_mcast rcv_probes_ucast  periodic_gc_runs forced_gc_runs\n");
+		seq_printf(seq, "entries  allocs destroys hash_grows  lookups hits  res_failed  rcv_probes_mcast rcv_probes_ucast  periodic_gc_runs forced_gc_runs unresolved_discards\n");
 		return 0;
 	}
 
 	seq_printf(seq, "%08x  %08lx %08lx %08lx  %08lx %08lx  %08lx  "
-			"%08lx %08lx  %08lx %08lx\n",
+			"%08lx %08lx  %08lx %08lx %08lx\n",
 		   atomic_read(&tbl->entries),
 
 		   st->allocs,
@@ -2303,7 +2304,8 @@ static int neigh_stat_seq_show(struct seq_file *seq, void *v)
 		   st->rcv_probes_ucast,
 
 		   st->periodic_gc_runs,
-		   st->forced_gc_runs
+		   st->forced_gc_runs,
+		   st->unres_discards
 		   );
 
 	return 0;