SUNRPC: Add refcounting to the struct rpc_xprt

In a subsequent patch, this will allow the portmapper to take a reference
to the rpc_xprt for which it is updating the port number, fixing an Oops.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/xprt.h

@@ -12,6 +12,7 @@
 #include <linux/uio.h>
 #include <linux/socket.h>
 #include <linux/in.h>
+#include <linux/kref.h>
 #include <linux/sunrpc/sched.h>
 #include <linux/sunrpc/xdr.h>
 
@@ -129,6 +130,7 @@ struct rpc_xprt_ops {
 };
 
 struct rpc_xprt {
+	struct kref		kref;		/* Reference count */
 	struct rpc_xprt_ops *	ops;		/* transport methods */
 	struct socket *		sock;		/* BSD socket layer */
 	struct sock *		inet;		/* INET layer */
@@ -248,7 +250,8 @@ int			xprt_adjust_timeout(struct rpc_rqst *req);
 void			xprt_release_xprt(struct rpc_xprt *xprt, struct rpc_task *task);
 void			xprt_release_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task);
 void			xprt_release(struct rpc_task *task);
-int			xprt_destroy(struct rpc_xprt *xprt);
+struct rpc_xprt *	xprt_get(struct rpc_xprt *xprt);
+void			xprt_put(struct rpc_xprt *xprt);
 
 static inline u32 *xprt_skip_transport_header(struct rpc_xprt *xprt, u32 *p)
 {

net/sunrpc/clnt.c

@@ -177,7 +177,7 @@ static struct rpc_clnt * rpc_new_client(struct rpc_xprt *xprt, char *servname, s
 		kfree(clnt->cl_server);
 	kfree(clnt);
 out_err:
-	xprt_destroy(xprt);
+	xprt_put(xprt);
 out_no_xprt:
 	return ERR_PTR(err);
 }
@@ -261,6 +261,7 @@ rpc_clone_client(struct rpc_clnt *clnt)
 	atomic_set(&new->cl_users, 0);
 	new->cl_parent = clnt;
 	atomic_inc(&clnt->cl_count);
+	new->cl_xprt = xprt_get(clnt->cl_xprt);
 	/* Turn off autobind on clones */
 	new->cl_autobind = 0;
 	new->cl_oneshot = 0;
@@ -337,15 +338,12 @@ rpc_destroy_client(struct rpc_clnt *clnt)
 		rpc_rmdir(clnt->cl_dentry);
 		rpc_put_mount();
 	}
-	if (clnt->cl_xprt) {
-		xprt_destroy(clnt->cl_xprt);
-		clnt->cl_xprt = NULL;
-	}
 	if (clnt->cl_server != clnt->cl_inline_name)
 		kfree(clnt->cl_server);
 out_free:
 	rpc_free_iostats(clnt->cl_metrics);
 	clnt->cl_metrics = NULL;
+	xprt_put(clnt->cl_xprt);
 	kfree(clnt);
 	return 0;
 }

net/sunrpc/xprt.c

@@ -926,6 +926,7 @@ struct rpc_xprt *xprt_create_transport(int proto, struct sockaddr *ap, size_t si
 		return ERR_PTR(result);
 	}
 
+	kref_init(&xprt->kref);
 	spin_lock_init(&xprt->transport_lock);
 	spin_lock_init(&xprt->reserve_lock);
 
@@ -958,16 +959,37 @@ struct rpc_xprt *xprt_create_transport(int proto, struct sockaddr *ap, size_t si
 
 /**
  * xprt_destroy - destroy an RPC transport, killing off all requests.
- * @xprt: transport to destroy
+ * @kref: kref for the transport to destroy
  *
  */
-int xprt_destroy(struct rpc_xprt *xprt)
+static void xprt_destroy(struct kref *kref)
 {
+	struct rpc_xprt *xprt = container_of(kref, struct rpc_xprt, kref);
+
 	dprintk("RPC:      destroying transport %p\n", xprt);
 	xprt->shutdown = 1;
 	del_timer_sync(&xprt->timer);
 	xprt->ops->destroy(xprt);
 	kfree(xprt);
+}
 
-	return 0;
+/**
+ * xprt_put - release a reference to an RPC transport.
+ * @xprt: pointer to the transport
+ *
+ */
+void xprt_put(struct rpc_xprt *xprt)
+{
+	kref_put(&xprt->kref, xprt_destroy);
+}
+
+/**
+ * xprt_get - return a reference to an RPC transport.
+ * @xprt: pointer to the transport
+ *
+ */
+struct rpc_xprt *xprt_get(struct rpc_xprt *xprt)
+{
+	kref_get(&xprt->kref);
+	return xprt;
 }