[SCTP]: Convert bind_addr_list locking to RCU

Since the sctp_sockaddr_entry is now RCU enabled as part of
the patch to synchronize sctp_localaddr_list, it makes sense to
change all handling of these entries to RCU.  This includes the
sctp_bind_addrs structure and it's list of bound addresses.

This list is currently protected by an external rw_lock and that
looks like an overkill.  There are only 2 writers to the list:
bind()/bindx() calls, and BH processing of ASCONF-ACK chunks.
These are already seriealized via the socket lock, so they will
not step on each other.  These are also relatively rare, so we
should be good with RCU.

The readers are varied and they are easily converted to RCU.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Sridhar Samdurala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 45 insertions, 23 deletions

diff --git a/net/sctp/bind_addr.c b/net/sctp/bind_addr.c
index 7fc369f9035d..d35cbf5aae33 100644
--- a/net/sctp/bind_addr.c
+++ b/net/sctp/bind_addr.c
@@ -167,7 +167,11 @@ int sctp_add_bind_addr(struct sctp_bind_addr *bp, union sctp_addr *new,
 
         INIT_LIST_HEAD(&addr->list);
         INIT_RCU_HEAD(&addr->rcu);
-        list_add_tail(&addr->list, &bp->address_list);
+
+        /* We always hold a socket lock when calling this function,
+         * and that acts as a writer synchronizing lock.
+         */
+        list_add_tail_rcu(&addr->list, &bp->address_list);
         SCTP_DBG_OBJCNT_INC(addr);
 
         return 0;
@@ -176,23 +180,35 @@ int sctp_add_bind_addr(struct sctp_bind_addr *bp, union sctp_addr *new,
 /* Delete an address from the bind address list in the SCTP_bind_addr
  * structure.
  */
-int sctp_del_bind_addr(struct sctp_bind_addr *bp, union sctp_addr *del_addr)
+int sctp_del_bind_addr(struct sctp_bind_addr *bp, union sctp_addr *del_addr,
+                        void (*rcu_call)(struct rcu_head *head,
+                                         void (*func)(struct rcu_head *head)))
 {
-        struct list_head *pos, *temp;
-        struct sctp_sockaddr_entry *addr;
+        struct sctp_sockaddr_entry *addr, *temp;
 
-        list_for_each_safe(pos, temp, &bp->address_list) {
-                addr = list_entry(pos, struct sctp_sockaddr_entry, list);
+        /* We hold the socket lock when calling this function,
+         * and that acts as a writer synchronizing lock.
+         */
+        list_for_each_entry_safe(addr, temp, &bp->address_list, list) {
                 if (sctp_cmp_addr_exact(&addr->a, del_addr)) {
                         /* Found the exact match. */
-                        list_del(pos);
-                        kfree(addr);
-                        SCTP_DBG_OBJCNT_DEC(addr);
-
-                        return 0;
+                        addr->valid = 0;
+                        list_del_rcu(&addr->list);
+                        break;
                 }
         }
 
+        /* Call the rcu callback provided in the args.  This function is
+         * called by both BH packet processing and user side socket option
+         * processing, but it works on different lists in those 2 contexts.
+         * Each context provides it's own callback, whether call_rcu_bh()
+         * or call_rcu(), to make sure that we wait for an appropriate time.
+         */
+        if (addr && !addr->valid) {
+                rcu_call(&addr->rcu, sctp_local_addr_free);
+                SCTP_DBG_OBJCNT_DEC(addr);
+        }
+
         return -EINVAL;
 }
 
@@ -302,15 +318,20 @@ int sctp_bind_addr_match(struct sctp_bind_addr *bp,
                          struct sctp_sock *opt)
 {
         struct sctp_sockaddr_entry *laddr;
-        struct list_head *pos;
-
-        list_for_each(pos, &bp->address_list) {
-                laddr = list_entry(pos, struct sctp_sockaddr_entry, list);
-                if (opt->pf->cmp_addr(&laddr->a, addr, opt))
-                        return 1;
+        int match = 0;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(laddr, &bp->address_list, list) {
+                if (!laddr->valid)
+                        continue;
+                if (opt->pf->cmp_addr(&laddr->a, addr, opt)) {
+                        match = 1;
+                        break;
+                }
         }
+        rcu_read_unlock();
 
-        return 0;
+        return match;
 }
 
 /* Find the first address in the bind address list that is not present in
@@ -325,18 +346,19 @@ union sctp_addr *sctp_find_unmatch_addr(struct sctp_bind_addr	*bp,
         union sctp_addr                 *addr;
         void                            *addr_buf;
         struct sctp_af                  *af;
-        struct list_head                *pos;
         int                             i;
 
-        list_for_each(pos, &bp->address_list) {
-                laddr = list_entry(pos, struct sctp_sockaddr_entry, list);
-
+        /* This is only called sctp_send_asconf_del_ip() and we hold
+         * the socket lock in that code patch, so that address list
+         * can't change.
+         */
+        list_for_each_entry(laddr, &bp->address_list, list) {
                 addr_buf = (union sctp_addr *)addrs;
                 for (i = 0; i < addrcnt; i++) {
                         addr = (union sctp_addr *)addr_buf;
                         af = sctp_get_af_specific(addr->v4.sin_family);
                         if (!af)
-                                return NULL;
+                                break;
 
                         if (opt->pf->cmp_addr(&laddr->a, addr, opt))
                                 break;