linux/include/net/arp.h
Eric Dumazet 25c7a6d1f9 net: avoid potential false sharing in neighbor related code
There are common instances of the following construct :

	if (n->confirmed != now)
		n->confirmed = now;

A C compiler could legally remove the conditional.

Use READ_ONCE()/WRITE_ONCE() to avoid this problem.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2019-11-06 16:14:48 -08:00

83 lines
2.0 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
/* linux/net/inet/arp.h */
#ifndef _ARP_H
#define _ARP_H
#include <linux/if_arp.h>
#include <linux/hash.h>
#include <net/neighbour.h>
extern struct neigh_table arp_tbl;
static inline u32 arp_hashfn(const void *pkey, const struct net_device *dev, u32 *hash_rnd)
{
u32 key = *(const u32 *)pkey;
u32 val = key ^ hash32_ptr(dev);
return val * hash_rnd[0];
}
#ifdef CONFIG_INET
static inline struct neighbour *__ipv4_neigh_lookup_noref(struct net_device *dev, u32 key)
{
if (dev->flags & (IFF_LOOPBACK | IFF_POINTOPOINT))
key = INADDR_ANY;
return ___neigh_lookup_noref(&arp_tbl, neigh_key_eq32, arp_hashfn, &key, dev);
}
#else
static inline
struct neighbour *__ipv4_neigh_lookup_noref(struct net_device *dev, u32 key)
{
return NULL;
}
#endif
static inline struct neighbour *__ipv4_neigh_lookup(struct net_device *dev, u32 key)
{
struct neighbour *n;
rcu_read_lock_bh();
n = __ipv4_neigh_lookup_noref(dev, key);
if (n && !refcount_inc_not_zero(&n->refcnt))
n = NULL;
rcu_read_unlock_bh();
return n;
}
static inline void __ipv4_confirm_neigh(struct net_device *dev, u32 key)
{
struct neighbour *n;
rcu_read_lock_bh();
n = __ipv4_neigh_lookup_noref(dev, key);
if (n) {
unsigned long now = jiffies;
/* avoid dirtying neighbour */
if (READ_ONCE(n->confirmed) != now)
WRITE_ONCE(n->confirmed, now);
}
rcu_read_unlock_bh();
}
void arp_init(void);
int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg);
void arp_send(int type, int ptype, __be32 dest_ip,
struct net_device *dev, __be32 src_ip,
const unsigned char *dest_hw,
const unsigned char *src_hw, const unsigned char *th);
int arp_mc_map(__be32 addr, u8 *haddr, struct net_device *dev, int dir);
void arp_ifdown(struct net_device *dev);
struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,
struct net_device *dev, __be32 src_ip,
const unsigned char *dest_hw,
const unsigned char *src_hw,
const unsigned char *target_hw);
void arp_xmit(struct sk_buff *skb);
#endif /* _ARP_H */