ipvs: make the service replacement more robust

commit 578bc3ef1e473a ("ipvs: reorganize dest trash") added
IP_VS_DEST_STATE_REMOVING flag and RCU callback named
ip_vs_dest_wait_readers() to keep dests and services after
removal for at least a RCU grace period. But we have the
following corner cases:

- we can not reuse the same dest if its service is removed
while IP_VS_DEST_STATE_REMOVING is still set because another dest
removal in the first grace period can not extend this period.
It can happen when ipvsadm -C && ipvsadm -R is used.

- dest->svc can be replaced but ip_vs_in_stats() and
ip_vs_out_stats() have no explicit read memory barriers
when accessing dest->svc. It can happen that dest->svc
was just freed (replaced) while we use it to update
the stats.

We solve the problems as follows:

- IP_VS_DEST_STATE_REMOVING is removed and we ensure a fixed
idle period for the dest (IP_VS_DEST_TRASH_PERIOD). idle_start
will remember when for first time after deletion we noticed
dest->refcnt=0. Later, the connections can grab a reference
while in RCU grace period but if refcnt becomes 0 we can
safely free the dest and its svc.

- dest->svc becomes RCU pointer. As result, we add explicit
RCU locking in ip_vs_in_stats() and ip_vs_out_stats().

- __ip_vs_unbind_svc is renamed to __ip_vs_svc_put(), it
now can free the service immediately or after a RCU grace
period. dest->svc is not set to NULL anymore.

	As result, unlinked dests and their services are
freed always after IP_VS_DEST_TRASH_PERIOD period, unused
services are freed after a RCU grace period.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>

2 files changed, 45 insertions, 53 deletions

diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index 4f69e83ff836..74fd00c27210 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -116,6 +116,7 @@ ip_vs_in_stats(struct ip_vs_conn *cp, struct sk_buff *skb)
 
         if (dest && (dest->flags & IP_VS_DEST_F_AVAILABLE)) {
                 struct ip_vs_cpu_stats *s;
+                struct ip_vs_service *svc;
 
                 s = this_cpu_ptr(dest->stats.cpustats);
                 s->ustats.inpkts++;
@@ -123,11 +124,14 @@ ip_vs_in_stats(struct ip_vs_conn *cp, struct sk_buff *skb)
                 s->ustats.inbytes += skb->len;
                 u64_stats_update_end(&s->syncp);
 
-                s = this_cpu_ptr(dest->svc->stats.cpustats);
+                rcu_read_lock();
+                svc = rcu_dereference(dest->svc);
+                s = this_cpu_ptr(svc->stats.cpustats);
                 s->ustats.inpkts++;
                 u64_stats_update_begin(&s->syncp);
                 s->ustats.inbytes += skb->len;
                 u64_stats_update_end(&s->syncp);
+                rcu_read_unlock();
 
                 s = this_cpu_ptr(ipvs->tot_stats.cpustats);
                 s->ustats.inpkts++;
@@ -146,6 +150,7 @@ ip_vs_out_stats(struct ip_vs_conn *cp, struct sk_buff *skb)
 
         if (dest && (dest->flags & IP_VS_DEST_F_AVAILABLE)) {
                 struct ip_vs_cpu_stats *s;
+                struct ip_vs_service *svc;
 
                 s = this_cpu_ptr(dest->stats.cpustats);
                 s->ustats.outpkts++;
@@ -153,11 +158,14 @@ ip_vs_out_stats(struct ip_vs_conn *cp, struct sk_buff *skb)
                 s->ustats.outbytes += skb->len;
                 u64_stats_update_end(&s->syncp);
 
-                s = this_cpu_ptr(dest->svc->stats.cpustats);
+                rcu_read_lock();
+                svc = rcu_dereference(dest->svc);
+                s = this_cpu_ptr(svc->stats.cpustats);
                 s->ustats.outpkts++;
                 u64_stats_update_begin(&s->syncp);
                 s->ustats.outbytes += skb->len;
                 u64_stats_update_end(&s->syncp);
+                rcu_read_unlock();
 
                 s = this_cpu_ptr(ipvs->tot_stats.cpustats);
                 s->ustats.outpkts++;
diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index c8148e487386..a3df9bddc4f7 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -460,7 +460,7 @@ static inline void
 __ip_vs_bind_svc(struct ip_vs_dest *dest, struct ip_vs_service *svc)
 {
         atomic_inc(&svc->refcnt);
-        dest->svc = svc;
+        rcu_assign_pointer(dest->svc, svc);
 }
 
 static void ip_vs_service_free(struct ip_vs_service *svc)
@@ -470,18 +470,25 @@ static void ip_vs_service_free(struct ip_vs_service *svc)
         kfree(svc);
 }
 
-static void
-__ip_vs_unbind_svc(struct ip_vs_dest *dest)
+static void ip_vs_service_rcu_free(struct rcu_head *head)
 {
-        struct ip_vs_service *svc = dest->svc;
+        struct ip_vs_service *svc;
+
+        svc = container_of(head, struct ip_vs_service, rcu_head);
+        ip_vs_service_free(svc);
+}
 
-        dest->svc = NULL;
+static void __ip_vs_svc_put(struct ip_vs_service *svc, bool do_delay)
+{
         if (atomic_dec_and_test(&svc->refcnt)) {
                 IP_VS_DBG_BUF(3, "Removing service %u/%s:%u\n",
                               svc->fwmark,
                               IP_VS_DBG_ADDR(svc->af, &svc->addr),
                               ntohs(svc->port));
-                ip_vs_service_free(svc);
+                if (do_delay)
+                        call_rcu(&svc->rcu_head, ip_vs_service_rcu_free);
+                else
+                        ip_vs_service_free(svc);
         }
 }
 
@@ -667,11 +674,6 @@ ip_vs_trash_get_dest(struct ip_vs_service *svc, const union nf_inet_addr *daddr,
                               IP_VS_DBG_ADDR(svc->af, &dest->addr),
                               ntohs(dest->port),
                               atomic_read(&dest->refcnt));
-                /* We can not reuse dest while in grace period
-                 * because conns still can use dest->svc
-                 */
-                if (test_bit(IP_VS_DEST_STATE_REMOVING, &dest->state))
-                        continue;
                 if (dest->af == svc->af &&
                     ip_vs_addr_equal(svc->af, &dest->addr, daddr) &&
                     dest->port == dport &&
@@ -697,8 +699,10 @@ out:
 
 static void ip_vs_dest_free(struct ip_vs_dest *dest)
 {
+        struct ip_vs_service *svc = rcu_dereference_protected(dest->svc, 1);
+
         __ip_vs_dst_cache_reset(dest);
-        __ip_vs_unbind_svc(dest);
+        __ip_vs_svc_put(svc, false);
         free_percpu(dest->stats.cpustats);
         kfree(dest);
 }
@@ -771,6 +775,7 @@ __ip_vs_update_dest(struct ip_vs_service *svc, struct ip_vs_dest *dest,
                     struct ip_vs_dest_user_kern *udest, int add)
 {
         struct netns_ipvs *ipvs = net_ipvs(svc->net);
+        struct ip_vs_service *old_svc;
         struct ip_vs_scheduler *sched;
         int conn_flags;
 
@@ -792,13 +797,14 @@ __ip_vs_update_dest(struct ip_vs_service *svc, struct ip_vs_dest *dest,
         atomic_set(&dest->conn_flags, conn_flags);
 
         /* bind the service */
-        if (!dest->svc) {
+        old_svc = rcu_dereference_protected(dest->svc, 1);
+        if (!old_svc) {
                 __ip_vs_bind_svc(dest, svc);
         } else {
-                if (dest->svc != svc) {
-                        __ip_vs_unbind_svc(dest);
+                if (old_svc != svc) {
                         ip_vs_zero_stats(&dest->stats);
                         __ip_vs_bind_svc(dest, svc);
+                        __ip_vs_svc_put(old_svc, true);
                 }
         }
 
@@ -998,16 +1004,6 @@ ip_vs_edit_dest(struct ip_vs_service *svc, struct ip_vs_dest_user_kern *udest)
         return 0;
 }
 
-static void ip_vs_dest_wait_readers(struct rcu_head *head)
-{
-        struct ip_vs_dest *dest = container_of(head, struct ip_vs_dest,
-                                               rcu_head);
-
-        /* End of grace period after unlinking */
-        clear_bit(IP_VS_DEST_STATE_REMOVING, &dest->state);
-}
-
-
 /*
  *      Delete a destination (must be already unlinked from the service)
  */
@@ -1023,20 +1019,16 @@ static void __ip_vs_del_dest(struct net *net, struct ip_vs_dest *dest,
          */
         ip_vs_rs_unhash(dest);
 
-        if (!cleanup) {
-                set_bit(IP_VS_DEST_STATE_REMOVING, &dest->state);
-                call_rcu(&dest->rcu_head, ip_vs_dest_wait_readers);
-        }
-
         spin_lock_bh(&ipvs->dest_trash_lock);
         IP_VS_DBG_BUF(3, "Moving dest %s:%u into trash, dest->refcnt=%d\n",
                       IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port),
                       atomic_read(&dest->refcnt));
         if (list_empty(&ipvs->dest_trash) && !cleanup)
                 mod_timer(&ipvs->dest_trash_timer,
-                          jiffies + IP_VS_DEST_TRASH_PERIOD);
+                          jiffies + (IP_VS_DEST_TRASH_PERIOD >> 1));
         /* dest lives in trash without reference */
         list_add(&dest->t_list, &ipvs->dest_trash);
+        dest->idle_start = 0;
         spin_unlock_bh(&ipvs->dest_trash_lock);
         ip_vs_dest_put(dest);
 }
@@ -1108,24 +1100,30 @@ static void ip_vs_dest_trash_expire(unsigned long data)
         struct net *net = (struct net *) data;
         struct netns_ipvs *ipvs = net_ipvs(net);
         struct ip_vs_dest *dest, *next;
+        unsigned long now = jiffies;
 
         spin_lock(&ipvs->dest_trash_lock);
         list_for_each_entry_safe(dest, next, &ipvs->dest_trash, t_list) {
-                /* Skip if dest is in grace period */
-                if (test_bit(IP_VS_DEST_STATE_REMOVING, &dest->state))
-                        continue;
                 if (atomic_read(&dest->refcnt) > 0)
                         continue;
+                if (dest->idle_start) {
+                        if (time_before(now, dest->idle_start +
+                                             IP_VS_DEST_TRASH_PERIOD))
+                                continue;
+                } else {
+                        dest->idle_start = max(1UL, now);
+                        continue;
+                }
                 IP_VS_DBG_BUF(3, "Removing destination %u/%s:%u from trash\n",
                               dest->vfwmark,
-                              IP_VS_DBG_ADDR(dest->svc->af, &dest->addr),
+                              IP_VS_DBG_ADDR(dest->af, &dest->addr),
                               ntohs(dest->port));
                 list_del(&dest->t_list);
                 ip_vs_dest_free(dest);
         }
         if (!list_empty(&ipvs->dest_trash))
                 mod_timer(&ipvs->dest_trash_timer,
-                          jiffies + IP_VS_DEST_TRASH_PERIOD);
+                          jiffies + (IP_VS_DEST_TRASH_PERIOD >> 1));
         spin_unlock(&ipvs->dest_trash_lock);
 }
 
@@ -1320,14 +1318,6 @@ out:
         return ret;
 }
 
-static void ip_vs_service_rcu_free(struct rcu_head *head)
-{
-        struct ip_vs_service *svc;
-
-        svc = container_of(head, struct ip_vs_service, rcu_head);
-        ip_vs_service_free(svc);
-}
-
 /*
  *      Delete a service from the service list
  *      - The service must be unlinked, unlocked and not referenced!
@@ -1376,13 +1366,7 @@ static void __ip_vs_del_service(struct ip_vs_service *svc, bool cleanup)
         /*
          *    Free the service if nobody refers to it
          */
-        if (atomic_dec_and_test(&svc->refcnt)) {
-                IP_VS_DBG_BUF(3, "Removing service %u/%s:%u\n",
-                              svc->fwmark,
-                              IP_VS_DBG_ADDR(svc->af, &svc->addr),
-                              ntohs(svc->port));
-                call_rcu(&svc->rcu_head, ip_vs_service_rcu_free);
-        }
+        __ip_vs_svc_put(svc, true);
 
         /* decrease the module use count */
         ip_vs_use_count_dec();