net: add explicit logging and stat for neighbour table overflow

Add an explicit neighbour table overflow message (ratelimited) and
statistic to make diagnosing neighbour table overflows tractable in
the wild.

Diagnosing a neighbour table overflow can be quite difficult in the wild
because there is no explicit dmesg logged.  Callers to neighbour code
seem to use net_dbg_ratelimit when the neighbour call fails which means
the "base message" is not emitted and the callback suppressed messages
from the ratelimiting can end-up juxtaposed with unrelated messages.
Further, a forced garbage collection will increment a stat on each call
whether it was successful in freeing-up a table entry or not, so that
statistic is only a hint.  So, add a net_info_ratelimited message and
explicit statistic to the neighbour code.

Signed-off-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index bd33e66f49aa..8b683841e574 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -125,6 +125,7 @@ struct neigh_statistics {
 	unsigned long forced_gc_runs;	/* number of forced GC runs */
 
 	unsigned long unres_discards;	/* number of unresolved drops */
+	unsigned long table_fulls;      /* times even gc couldn't help */
 };
 
 #define NEIGH_CACHE_STAT_INC(tbl, field) this_cpu_inc((tbl)->stats->field)