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[PATCHv2 net 1/4] ipvs: make the service replacement more robust

To: Simon Horman <horms@xxxxxxxxxxxx>
Subject: [PATCHv2 net 1/4] ipvs: make the service replacement more robust
Cc: lvs-devel@xxxxxxxxxxxxxxx
From: Julian Anastasov <ja@xxxxxx>
Date: Thu, 12 Sep 2013 11:21:07 +0300
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@xxxxxx>
---
 include/net/ip_vs.h             |    7 +--
 net/netfilter/ipvs/ip_vs_core.c |   12 +++++-
 net/netfilter/ipvs/ip_vs_ctl.c  |   86 ++++++++++++++++-----------------------
 3 files changed, 47 insertions(+), 58 deletions(-)

diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index f0d70f0..c32360d 100644
--- a/include/net/ip_vs.h
+++ b/include/net/ip_vs.h
@@ -723,8 +723,6 @@ struct ip_vs_dest_dst {
        struct rcu_head         rcu_head;
 };
 
-/* In grace period after removing */
-#define IP_VS_DEST_STATE_REMOVING      0x01
 /*
  *     The real server destination forwarding entry
  *     with ip address, port number, and so on.
@@ -742,7 +740,7 @@ struct ip_vs_dest {
 
        atomic_t                refcnt;         /* reference counter */
        struct ip_vs_stats      stats;          /* statistics */
-       unsigned long           state;          /* state flags */
+       unsigned long           idle_start;     /* start time, jiffies */
 
        /* connection counters and thresholds */
        atomic_t                activeconns;    /* active connections */
@@ -756,14 +754,13 @@ struct ip_vs_dest {
        struct ip_vs_dest_dst __rcu *dest_dst;  /* cached dst info */
 
        /* for virtual service */
-       struct ip_vs_service    *svc;           /* service it belongs to */
+       struct ip_vs_service __rcu *svc;        /* service it belongs to */
        __u16                   protocol;       /* which protocol (TCP/UDP) */
        __be16                  vport;          /* virtual port number */
        union nf_inet_addr      vaddr;          /* virtual IP address */
        __u32                   vfwmark;        /* firewall mark of service */
 
        struct list_head        t_list;         /* in dest_trash */
-       struct rcu_head         rcu_head;
        unsigned int            in_rs_table:1;  /* we are in rs_table */
 };
 
diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index 4f69e83..74fd00c 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 c8148e4..a3df9bd 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();
-- 
1.7.3.4

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