neigh: Protect neigh->ha[] with a seqlock
Add a seqlock in struct neighbour to protect neigh->ha[], and avoid
dirtying neighbour in stress situation (many different flows / dsts)
Dirtying takes place because of read_lock(&n->lock) and n->used writes.
Switching to a seqlock, and writing n->used only on jiffies changes
permits less dirtying.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index a4538d5..f04e7a2 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -105,6 +105,7 @@
atomic_t refcnt;
atomic_t probes;
rwlock_t lock;
+ seqlock_t ha_lock;
unsigned char ha[ALIGN(MAX_ADDR_LEN, sizeof(unsigned long))];
struct hh_cache *hh;
int (*output)(struct sk_buff *skb);
@@ -302,7 +303,10 @@
static inline int neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
{
- neigh->used = jiffies;
+ unsigned long now = ACCESS_ONCE(jiffies);
+
+ if (neigh->used != now)
+ neigh->used = now;
if (!(neigh->nud_state&(NUD_CONNECTED|NUD_DELAY|NUD_PROBE)))
return __neigh_event_send(neigh, skb);
return 0;
@@ -373,4 +377,14 @@
#define NEIGH_CB(skb) ((struct neighbour_cb *)(skb)->cb)
+static inline void neigh_ha_snapshot(char *dst, const struct neighbour *n,
+ const struct net_device *dev)
+{
+ unsigned int seq;
+
+ do {
+ seq = read_seqbegin(&n->ha_lock);
+ memcpy(dst, n->ha, dev->addr_len);
+ } while (read_seqretry(&n->ha_lock, seq));
+}
#endif