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net: ipv4: fix RCU races on dst refcounts

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commit c6cffba4ff (ipv4: Fix input route performance regression.)
added various fatal races with dst refcounts.

crashes happen on tcp workloads if routes are added/deleted at the same
time.

The dst_free() calls from free_fib_info_rcu() are clearly racy.

We need instead regular dst refcounting (dst_release()) and make
sure dst_release() is aware of RCU grace periods :

Add DST_RCU_FREE flag so that dst_release() respects an RCU grace period
before dst destruction for cached dst

Introduce a new inet_sk_rx_dst_set() helper, using atomic_inc_not_zero()
to make sure we dont increase a zero refcount (On a dst currently
waiting an rcu grace period before destruction)

rt_cache_route() must take a reference on the new cached route, and
release it if was not able to install it.

With this patch, my machines survive various benchmarks.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2012-07-29 23:20:37 +00:00
committed by David S. Miller
parent cca32e4bf9
commit 404e0a8b6a
9 changed files with 55 additions and 35 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
net/ipv4/fib_semantics.c
View File

@@ -172,9 +172,9 @@ static void free_fib_info_rcu(struct rcu_head *head)
if (nexthop_nh->nh_exceptions)
free_nh_exceptions(nexthop_nh);
if (nexthop_nh->nh_rth_output)
dst_free(&nexthop_nh->nh_rth_output->dst);
dst_release(&nexthop_nh->nh_rth_output->dst);
if (nexthop_nh->nh_rth_input)
dst_free(&nexthop_nh->nh_rth_input->dst);
dst_release(&nexthop_nh->nh_rth_input->dst);
} endfor_nexthops(fi);
release_net(fi->fib_net);

16
net/ipv4/route.c
View File

@@ -1199,11 +1199,6 @@ restart:
fnhe->fnhe_stamp = jiffies;
}
static inline void rt_free(struct rtable *rt)
{
call_rcu_bh(&rt->dst.rcu_head, dst_rcu_free);
}
static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
{
struct rtable *orig, *prev, **p = &nh->nh_rth_output;
@@ -1213,17 +1208,14 @@ static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
orig = *p;
rt->dst.flags |= DST_RCU_FREE;
dst_hold(&rt->dst);
prev = cmpxchg(p, orig, rt);
if (prev == orig) {
if (orig)
rt_free(orig);
dst_release(&orig->dst);
} else {
/* Routes we intend to cache in the FIB nexthop have
* the DST_NOCACHE bit clear. However, if we are
* unsuccessful at storing this route into the cache
* we really need to set it.
*/
rt->dst.flags |= DST_NOCACHE;
dst_release(&rt->dst);
}
}

3
net/ipv4/tcp_input.c
View File

@@ -5604,8 +5604,7 @@ void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
tcp_set_state(sk, TCP_ESTABLISHED);
if (skb != NULL) {
sk->sk_rx_dst = dst_clone(skb_dst(skb));
inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
inet_sk_rx_dst_set(sk, skb);
security_inet_conn_established(sk, skb);
}

12
net/ipv4/tcp_ipv4.c
View File

@@ -1617,19 +1617,19 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
#endif
if (sk->sk_state == TCP_ESTABLISHED) { /* Fast path */
struct dst_entry *dst = sk->sk_rx_dst;
sock_rps_save_rxhash(sk, skb);
if (sk->sk_rx_dst) {
struct dst_entry *dst = sk->sk_rx_dst;
if (dst) {
if (inet_sk(sk)->rx_dst_ifindex != skb->skb_iif ||
dst->ops->check(dst, 0) == NULL) {
dst_release(dst);
sk->sk_rx_dst = NULL;
}
}
if (unlikely(sk->sk_rx_dst == NULL)) {
sk->sk_rx_dst = dst_clone(skb_dst(skb));
inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
}
if (unlikely(sk->sk_rx_dst == NULL))
inet_sk_rx_dst_set(sk, skb);
if (tcp_rcv_established(sk, skb, tcp_hdr(skb), skb->len)) {
rsk = sk;
goto reset;

3
net/ipv4/tcp_minisocks.c
View File

@@ -387,8 +387,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
struct tcp_sock *oldtp = tcp_sk(sk);
struct tcp_cookie_values *oldcvp = oldtp->cookie_values;
newsk->sk_rx_dst = dst_clone(skb_dst(skb));
inet_sk(newsk)->rx_dst_ifindex = skb->skb_iif;
inet_sk_rx_dst_set(newsk, skb);
/* TCP Cookie Transactions require space for the cookie pair,
* as it differs for each connection. There is no need to