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/net/core/neighbour.c b/net/core/neighbour.c
index 2044906..b165b96 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -294,6 +294,7 @@
skb_queue_head_init(&n->arp_queue);
rwlock_init(&n->lock);
+ seqlock_init(&n->ha_lock);
n->updated = n->used = now;
n->nud_state = NUD_NONE;
n->output = neigh_blackhole;
@@ -1015,7 +1016,7 @@
}
EXPORT_SYMBOL(__neigh_event_send);
-static void neigh_update_hhs(struct neighbour *neigh)
+static void neigh_update_hhs(const struct neighbour *neigh)
{
struct hh_cache *hh;
void (*update)(struct hh_cache*, const struct net_device*, const unsigned char *)
@@ -1151,7 +1152,9 @@
}
if (lladdr != neigh->ha) {
+ write_seqlock(&neigh->ha_lock);
memcpy(&neigh->ha, lladdr, dev->addr_len);
+ write_sequnlock(&neigh->ha_lock);
neigh_update_hhs(neigh);
if (!(new & NUD_CONNECTED))
neigh->confirmed = jiffies -
@@ -1214,6 +1217,7 @@
{
struct hh_cache *hh;
+ smp_rmb(); /* paired with smp_wmb() in neigh_hh_init() */
for (hh = n->hh; hh; hh = hh->hh_next) {
if (hh->hh_type == protocol) {
atomic_inc(&hh->hh_refcnt);
@@ -1248,8 +1252,8 @@
kfree(hh);
return;
}
- read_unlock(&n->lock);
- write_lock(&n->lock);
+
+ write_lock_bh(&n->lock);
/* must check if another thread already did the insert */
if (neigh_hh_lookup(n, dst, protocol)) {
@@ -1263,13 +1267,13 @@
hh->hh_output = n->ops->output;
hh->hh_next = n->hh;
+ smp_wmb(); /* paired with smp_rmb() in neigh_hh_lookup() */
n->hh = hh;
if (unlikely(cmpxchg(&dst->hh, NULL, hh) != NULL))
hh_cache_put(hh);
end:
- write_unlock(&n->lock);
- read_lock(&n->lock);
+ write_unlock_bh(&n->lock);
}
/* This function can be used in contexts, where only old dev_queue_xmit
@@ -1308,16 +1312,18 @@
if (!neigh_event_send(neigh, skb)) {
int err;
struct net_device *dev = neigh->dev;
+ unsigned int seq;
- read_lock_bh(&neigh->lock);
if (dev->header_ops->cache &&
!dst->hh &&
!(dst->flags & DST_NOCACHE))
neigh_hh_init(neigh, dst, dst->ops->protocol);
- err = dev_hard_header(skb, dev, ntohs(skb->protocol),
- neigh->ha, NULL, skb->len);
- read_unlock_bh(&neigh->lock);
+ do {
+ seq = read_seqbegin(&neigh->ha_lock);
+ err = dev_hard_header(skb, dev, ntohs(skb->protocol),
+ neigh->ha, NULL, skb->len);
+ } while (read_seqretry(&neigh->ha_lock, seq));
if (err >= 0)
rc = neigh->ops->queue_xmit(skb);
@@ -1344,13 +1350,16 @@
struct dst_entry *dst = skb_dst(skb);
struct neighbour *neigh = dst->neighbour;
struct net_device *dev = neigh->dev;
+ unsigned int seq;
__skb_pull(skb, skb_network_offset(skb));
- read_lock_bh(&neigh->lock);
- err = dev_hard_header(skb, dev, ntohs(skb->protocol),
- neigh->ha, NULL, skb->len);
- read_unlock_bh(&neigh->lock);
+ do {
+ seq = read_seqbegin(&neigh->ha_lock);
+ err = dev_hard_header(skb, dev, ntohs(skb->protocol),
+ neigh->ha, NULL, skb->len);
+ } while (read_seqretry(&neigh->ha_lock, seq));
+
if (err >= 0)
err = neigh->ops->queue_xmit(skb);
else {
@@ -2148,10 +2157,14 @@
read_lock_bh(&neigh->lock);
ndm->ndm_state = neigh->nud_state;
- if ((neigh->nud_state & NUD_VALID) &&
- nla_put(skb, NDA_LLADDR, neigh->dev->addr_len, neigh->ha) < 0) {
- read_unlock_bh(&neigh->lock);
- goto nla_put_failure;
+ if (neigh->nud_state & NUD_VALID) {
+ char haddr[MAX_ADDR_LEN];
+
+ neigh_ha_snapshot(haddr, neigh, neigh->dev);
+ if (nla_put(skb, NDA_LLADDR, neigh->dev->addr_len, haddr) < 0) {
+ read_unlock_bh(&neigh->lock);
+ goto nla_put_failure;
+ }
}
ci.ndm_used = jiffies_to_clock_t(now - neigh->used);