[PATCH] PATCH 15/16: NFSD: TCP: Limit number of active tcp connections to an RPC service

Limit number of active tcp connections to an RPC service

If a connection comes in and that results in number of
connections being more than 5 times the number of threads,
then we close a connection.

We randomly drop with the oldest or the newest connection.

Thus if we are flooded with connection requests, some will
get in and hopefully stay long enough to service at least one request.

include/linux/sunrpc/svc.h

@@ -38,6 +38,7 @@ struct svc_serv {
 
 	struct list_head	sv_permsocks;	/* all permanent sockets */
 	struct list_head	sv_tempsocks;	/* all temporary sockets */
+	int			sv_tmpcnt;	/* count of temporary sockets */
 
 	char *			sv_name;	/* service name */
 };

net/sunrpc/svcsock.c

@@ -243,10 +243,25 @@ void svc_reserve(struct svc_rqst *rqstp, int space)
  * Release a socket after use.
  */
 static inline void
+svc_sock_put(struct svc_sock *svsk)
+{
+	struct svc_serv *serv = svsk->sk_server;
+
+	spin_lock_bh(&serv->sv_lock);
+	if (!--(svsk->sk_inuse) && test_bit(SK_DEAD, &svsk->sk_flags)) {
+		spin_unlock_bh(&serv->sv_lock);
+		dprintk("svc: releasing dead socket\n");
+		sock_release(svsk->sk_sock);
+		kfree(svsk);
+	}
+	else
+		spin_unlock_bh(&serv->sv_lock);
+}
+
+static void
 svc_sock_release(struct svc_rqst *rqstp)
 {
 	struct svc_sock	*svsk = rqstp->rq_sock;
-	struct svc_serv	*serv = svsk->sk_server;
 
 	svc_release_skb(rqstp);
 
@@ -265,15 +280,7 @@ svc_sock_release(struct svc_rqst *rqstp)
 	svc_reserve(rqstp, 0);
 	rqstp->rq_sock = NULL;
 
-	spin_lock_bh(&serv->sv_lock);
-	if (!--(svsk->sk_inuse) && test_bit(SK_DEAD, &svsk->sk_flags)) {
-		spin_unlock_bh(&serv->sv_lock);
-		dprintk("svc: releasing dead socket\n");
-		sock_release(svsk->sk_sock);
-		kfree(svsk);
-	}
-	else
-		spin_unlock_bh(&serv->sv_lock);
+	svc_sock_put(svsk);
 }
 
 /*
@@ -698,6 +705,35 @@ svc_tcp_accept(struct svc_sock *svsk)
 	set_bit(SK_DATA, &newsvsk->sk_flags);
 	svc_sock_enqueue(newsvsk);
 
+	/* make sure that we don't have too many active connections.
+	 * If we have, something must be dropped.
+	 * We randomly choose between newest and oldest (in terms
+	 * of recent activity) and drop it.
+	 */
+	if (serv->sv_tmpcnt > serv->sv_nrthreads*5) {
+		struct svc_sock *svsk = NULL;
+		spin_lock_bh(&serv->sv_lock);
+		if (!list_empty(&serv->sv_tempsocks)) {
+			if (net_random()&1)
+				svsk = list_entry(serv->sv_tempsocks.prev,
+						  struct svc_sock,
+						  sk_list);
+			else
+				svsk = list_entry(serv->sv_tempsocks.next,
+						  struct svc_sock,
+						  sk_list);
+			set_bit(SK_CLOSE, &svsk->sk_flags);
+			svsk->sk_inuse ++;
+		}
+		spin_unlock_bh(&serv->sv_lock);
+
+		if (svsk) {
+			svc_sock_enqueue(svsk);
+			svc_sock_put(svsk);
+		}
+
+	}
+
 	if (serv->sv_stats)
 		serv->sv_stats->nettcpconn++;
 
@@ -1138,6 +1174,7 @@ if (svsk->sk_sk == NULL)
 	if (!pmap_register) {
 		set_bit(SK_TEMP, &svsk->sk_flags);
 		list_add(&svsk->sk_list, &serv->sv_tempsocks);
+		serv->sv_tmpcnt++;
 	} else {
 		clear_bit(SK_TEMP, &svsk->sk_flags);
 		list_add(&svsk->sk_list, &serv->sv_permsocks);
@@ -1217,6 +1254,8 @@ svc_delete_socket(struct svc_sock *svsk)
 	spin_lock_bh(&serv->sv_lock);
 
 	list_del(&svsk->sk_list);
+	if (test_bit(SK_TEMP, &svsk->sk_flags))
+		serv->sv_tmpcnt--;
 	if (test_bit(SK_QUED, &svsk->sk_flags))
 		list_del(&svsk->sk_ready);