net: ipv4: fix RCU races on dst refcounts

commit c6cffba4ffa2 (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>

1 files changed, 1 insertions, 2 deletions

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 3f1cc2028edd..232a90c3ec86 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -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