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>

1 files changed, 2 insertions, 5 deletions

diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index fe782ed2fe72..9c4d37ec45a1 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 */
 };