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>

diff --git a/include/net/dst.h b/include/net/dst.h
index baf59789006427bc7c373449b62b271e6e777d15..31a9fd39edb6b10fc283e1a8680dc3f63e3dbfee 100644 (file)
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -61,6 +61,7 @@ struct dst_entry {
 #define DST_NOPEER             0x0040
 #define DST_FAKE_RTABLE                0x0080
 #define DST_XFRM_TUNNEL                0x0100
+#define DST_RCU_FREE           0x0200
 
        unsigned short          pending_confirm;
 
@@ -382,12 +383,6 @@ static inline void dst_free(struct dst_entry *dst)
        __dst_free(dst);
 }
 
-static inline void dst_rcu_free(struct rcu_head *head)
-{
-       struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
-       dst_free(dst);
-}
-
 static inline void dst_confirm(struct dst_entry *dst)
 {
        dst->pending_confirm = 1;

diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 613cfa4016728300da88a8fc6f1f664de99da5cc..e3fd34c83ac95554280754df6bd34dc54343a8d7 100644 (file)
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -249,4 +249,17 @@ static inline __u8 inet_sk_flowi_flags(const struct sock *sk)
        return flags;
 }
 
+static inline void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb)
+{
+       struct dst_entry *dst = skb_dst(skb);
+
+       if (atomic_inc_not_zero(&dst->__refcnt)) {
+               if (!(dst->flags & DST_RCU_FREE))
+                       dst->flags |= DST_RCU_FREE;
+
+               sk->sk_rx_dst = dst;
+               inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
+       }
+}
+
 #endif /* _INET_SOCK_H */

diff --git a/net/core/dst.c b/net/core/dst.c
index 069d51d29414a3245f9b60b66c534f78ce3b1752..d9e33ebe170fc42d757504e4a1392bf16e5933a1 100644 (file)
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -258,6 +258,15 @@ again:
 }
 EXPORT_SYMBOL(dst_destroy);
 
+static void dst_rcu_destroy(struct rcu_head *head)
+{
+       struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
+
+       dst = dst_destroy(dst);
+       if (dst)
+               __dst_free(dst);
+}
+
 void dst_release(struct dst_entry *dst)
 {
        if (dst) {
@@ -265,10 +274,14 @@ void dst_release(struct dst_entry *dst)
 
                newrefcnt = atomic_dec_return(&dst->__refcnt);
                WARN_ON(newrefcnt < 0);
-               if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {
-                       dst = dst_destroy(dst);
-                       if (dst)
-                               __dst_free(dst);
+               if (unlikely(dst->flags & (DST_NOCACHE | DST_RCU_FREE)) && !newrefcnt) {
+                       if (dst->flags & DST_RCU_FREE) {
+                               call_rcu_bh(&dst->rcu_head, dst_rcu_destroy);
+                       } else {
+                               dst = dst_destroy(dst);
+                               if (dst)
+                                       __dst_free(dst);
+                       }
                }
        }
 }
@@ -320,11 +333,14 @@ EXPORT_SYMBOL(__dst_destroy_metrics_generic);
  */
 void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
 {
+       bool hold;
+
        WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
        /* If dst not in cache, we must take a reference, because
         * dst_release() will destroy dst as soon as its refcount becomes zero
         */
-       if (unlikely(dst->flags & DST_NOCACHE)) {
+       hold = (dst->flags & (DST_NOCACHE | DST_RCU_FREE)) == DST_NOCACHE;
+       if (unlikely(hold)) {
                dst_hold(dst);
                skb_dst_set(skb, dst);
        } else {

diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index 85a3604c87c8d2cac6cac4d7049d9ba75877bf66..26719779ad8ee595d013beed4987ce8b6d591e41 100644 (file)
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -184,6 +184,12 @@ static __inline__ unsigned int dn_hash(__le16 src, __le16 dst)
        return dn_rt_hash_mask & (unsigned int)tmp;
 }
 
+static inline void dst_rcu_free(struct rcu_head *head)
+{
+       struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
+       dst_free(dst);
+}
+
 static inline void dnrt_free(struct dn_route *rt)
 {
        call_rcu_bh(&rt->dst.rcu_head, dst_rcu_free);

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index da0cc2e6b2500f89850642aa8e2d50d26d6a2ae3..e55171f184f9731274c568345b9b74c14b2e63cc 100644 (file)
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -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);

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index fc1a81ca79a7837d4307cb2a9bb034630c99b1a2..d6eabcfe8a9089c315cb6b812d1d327e4fdf1406 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -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);
        }
 }
 

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a356e1fecf9ad7782db4373b1b03d3f20ba604b3..9be30b039ae3ca7493d5fa37c3556da82ddf4229 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -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);
        }
 

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2fbd9921253fac33d4f41d517c3316c0fc008acb..7f91e5ac827794161bef2da2584a936680fd3daf 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -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;

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 3f1cc2028edde57d9defebb693cfb603bf956bab..232a90c3ec8695dfa740fe141ba113074f99a289 100644 (file)
--- 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