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neigh: Protect neigh->ha[] with a seqlock

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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>
This commit is contained in:
Eric Dumazet
2010-10-07 10:44:07 +00:00
committed by David S. Miller
parent d122179a3c
commit 0ed8ddf404
4 changed files with 51 additions and 26 deletions
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16
include/net/neighbour.h
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@@ -105,6 +105,7 @@ struct neighbour {
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 void neigh_confirm(struct neighbour *neigh)
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 @@ struct neighbour_cb {
#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