IB/iser: Simplify connection management

iSER relies on refcounting to manage iser connections establishment
and teardown.

Following commit 39ff05dbbbdb ("IB/iser: Enhance disconnection logic
for multi-pathing"), iser connection maintain 3 references:

 - iscsi_endpoint (at creation stage)
 - cma_id (at connection request stage)
 - iscsi_conn (at bind stage)

We can avoid taking explicit refcounts by correctly serializing iser
teardown flows (graceful and non-graceful).

Our approach is to trigger a scheduled work to handle ordered teardown
by gracefully waiting for 2 cleanup stages to complete:

 1. Cleanup of live pending tasks indicated by iscsi_conn_stop completion
 2. Flush errors processing

Each completed stage will notify a waiting worker thread when it is
done to allow teardwon continuation.

Since iSCSI connection establishment may trigger endpoint disconnect
without a successful endpoint connect, we rely on the iscsi <-> iser
binding (.conn_bind) to learn about the teardown policy we should take
wrt cleanup stages.

Since all cleanup worker threads are scheduled (release_wq) in
.ep_disconnect it is safe to assume that when module_exit is called,
all cleanup workers are already scheduled. Thus proper module unload
shall flush all scheduled works before allowing safe exit, to
guarantee no resources got left behind.

Signed-off-by: Ariel Nahum <arieln@mellanox.com>
Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/iser/iscsi_iser.c

@@ -99,6 +99,7 @@ MODULE_PARM_DESC(pi_enable, "Enable T10-PI offload support (default:disabled)");
 module_param_named(pi_guard, iser_pi_guard, int, 0644);
 MODULE_PARM_DESC(pi_guard, "T10-PI guard_type, 0:CRC|1:IP_CSUM (default:CRC)");
 
+static struct workqueue_struct *release_wq;
 struct iser_global ig;
 
 void
@@ -337,24 +338,6 @@ iscsi_iser_conn_create(struct iscsi_cls_session *cls_session, uint32_t conn_idx)
 	return cls_conn;
 }
 
-static void
-iscsi_iser_conn_destroy(struct iscsi_cls_conn *cls_conn)
-{
-	struct iscsi_conn *conn = cls_conn->dd_data;
-	struct iser_conn *ib_conn = conn->dd_data;
-
-	iscsi_conn_teardown(cls_conn);
-	/*
-	 * Userspace will normally call the stop callback and
-	 * already have freed the ib_conn, but if it goofed up then
-	 * we free it here.
-	 */
-	if (ib_conn) {
-		ib_conn->iscsi_conn = NULL;
-		iser_conn_put(ib_conn, 1); /* deref iscsi/ib conn unbinding */
-	}
-}
-
 static int
 iscsi_iser_conn_bind(struct iscsi_cls_session *cls_session,
 		     struct iscsi_cls_conn *cls_conn, uint64_t transport_eph,
@@ -392,29 +375,39 @@ iscsi_iser_conn_bind(struct iscsi_cls_session *cls_session,
 	conn->dd_data = ib_conn;
 	ib_conn->iscsi_conn = conn;
 
-	iser_conn_get(ib_conn); /* ref iscsi/ib conn binding */
 	return 0;
 }
 
+static int
+iscsi_iser_conn_start(struct iscsi_cls_conn *cls_conn)
+{
+	struct iscsi_conn *iscsi_conn;
+	struct iser_conn *ib_conn;
+
+	iscsi_conn = cls_conn->dd_data;
+	ib_conn = iscsi_conn->dd_data;
+	reinit_completion(&ib_conn->stop_completion);
+
+	return iscsi_conn_start(cls_conn);
+}
+
 static void
 iscsi_iser_conn_stop(struct iscsi_cls_conn *cls_conn, int flag)
 {
 	struct iscsi_conn *conn = cls_conn->dd_data;
 	struct iser_conn *ib_conn = conn->dd_data;
 
+	iser_dbg("stopping iscsi_conn: %p, ib_conn: %p\n", conn, ib_conn);
+	iscsi_conn_stop(cls_conn, flag);
+
 	/*
 	 * Userspace may have goofed up and not bound the connection or
 	 * might have only partially setup the connection.
 	 */
 	if (ib_conn) {
-		iscsi_conn_stop(cls_conn, flag);
-		/*
-		 * There is no unbind event so the stop callback
-		 * must release the ref from the bind.
-		 */
-		iser_conn_put(ib_conn, 1); /* deref iscsi/ib conn unbinding */
+		conn->dd_data = NULL;
+		complete(&ib_conn->stop_completion);
 	}
-	conn->dd_data = NULL;
 }
 
 static void iscsi_iser_session_destroy(struct iscsi_cls_session *cls_session)
@@ -652,19 +645,20 @@ iscsi_iser_ep_disconnect(struct iscsi_endpoint *ep)
 	struct iser_conn *ib_conn;
 
 	ib_conn = ep->dd_data;
-	if (ib_conn->iscsi_conn)
-		/*
-		 * Must suspend xmit path if the ep is bound to the
-		 * iscsi_conn, so we know we are not accessing the ib_conn
-		 * when we free it.
-		 *
-		 * This may not be bound if the ep poll failed.
-		 */
-		iscsi_suspend_tx(ib_conn->iscsi_conn);
-
-
-	iser_info("ib conn %p state %d\n", ib_conn, ib_conn->state);
+	iser_info("ep %p ib conn %p state %d\n", ep, ib_conn, ib_conn->state);
 	iser_conn_terminate(ib_conn);
+
+	/*
+	 * if iser_conn and iscsi_conn are bound, we must wait iscsi_conn_stop
+	 * call and ISER_CONN_DOWN state before freeing the iser resources.
+	 * otherwise we are safe to free resources immediately.
+	 */
+	if (ib_conn->iscsi_conn) {
+		INIT_WORK(&ib_conn->release_work, iser_release_work);
+		queue_work(release_wq, &ib_conn->release_work);
+	} else {
+		iser_conn_release(ib_conn);
+	}
 }
 
 static umode_t iser_attr_is_visible(int param_type, int param)
@@ -748,13 +742,13 @@ static struct iscsi_transport iscsi_iser_transport = {
 	/* connection management */
 	.create_conn            = iscsi_iser_conn_create,
 	.bind_conn              = iscsi_iser_conn_bind,
-	.destroy_conn           = iscsi_iser_conn_destroy,
+	.destroy_conn           = iscsi_conn_teardown,
 	.attr_is_visible	= iser_attr_is_visible,
 	.set_param              = iscsi_iser_set_param,
 	.get_conn_param		= iscsi_conn_get_param,
 	.get_ep_param		= iscsi_iser_get_ep_param,
 	.get_session_param	= iscsi_session_get_param,
-	.start_conn             = iscsi_conn_start,
+	.start_conn             = iscsi_iser_conn_start,
 	.stop_conn              = iscsi_iser_conn_stop,
 	/* iscsi host params */
 	.get_host_param		= iscsi_host_get_param,
@@ -801,6 +795,12 @@ static int __init iser_init(void)
 	mutex_init(&ig.connlist_mutex);
 	INIT_LIST_HEAD(&ig.connlist);
 
+	release_wq = alloc_workqueue("release workqueue", 0, 0);
+	if (!release_wq) {
+		iser_err("failed to allocate release workqueue\n");
+		return -ENOMEM;
+	}
+
 	iscsi_iser_scsi_transport = iscsi_register_transport(
 							&iscsi_iser_transport);
 	if (!iscsi_iser_scsi_transport) {
@@ -819,7 +819,24 @@ register_transport_failure:
 
 static void __exit iser_exit(void)
 {
+	struct iser_conn *ib_conn, *n;
+	int connlist_empty;
+
 	iser_dbg("Removing iSER datamover...\n");
+	destroy_workqueue(release_wq);
+
+	mutex_lock(&ig.connlist_mutex);
+	connlist_empty = list_empty(&ig.connlist);
+	mutex_unlock(&ig.connlist_mutex);
+
+	if (!connlist_empty) {
+		iser_err("Error cleanup stage completed but we still have iser "
+			 "connections, destroying them anyway.\n");
+		list_for_each_entry_safe(ib_conn, n, &ig.connlist, conn_list) {
+			iser_conn_release(ib_conn);
+		}
+	}
+
 	iscsi_unregister_transport(&iscsi_iser_transport);
 	kmem_cache_destroy(ig.desc_cache);
 }

drivers/infiniband/ulp/iser/iscsi_iser.h

@@ -333,6 +333,8 @@ struct iser_conn {
 	int                          post_recv_buf_count; /* posted rx count  */
 	atomic_t                     post_send_buf_count; /* posted tx count   */
 	char 			     name[ISER_OBJECT_NAME_SIZE];
+	struct work_struct	     release_work;
+	struct completion	     stop_completion;
 	struct list_head	     conn_list;       /* entry in ig conn list */
 
 	char  			     *login_buf;
@@ -417,12 +419,12 @@ void iscsi_iser_recv(struct iscsi_conn *conn,
 
 void iser_conn_init(struct iser_conn *ib_conn);
 
-void iser_conn_get(struct iser_conn *ib_conn);
-
-int iser_conn_put(struct iser_conn *ib_conn, int destroy_cma_id_allowed);
+void iser_conn_release(struct iser_conn *ib_conn);
 
 void iser_conn_terminate(struct iser_conn *ib_conn);
 
+void iser_release_work(struct work_struct *work);
+
 void iser_rcv_completion(struct iser_rx_desc *desc,
 			 unsigned long    dto_xfer_len,
 			struct iser_conn *ib_conn);

drivers/infiniband/ulp/iser/iser_verbs.c

@@ -581,14 +581,30 @@ static int iser_conn_state_comp_exch(struct iser_conn *ib_conn,
 	return ret;
 }
 
+void iser_release_work(struct work_struct *work)
+{
+	struct iser_conn *ib_conn;
+
+	ib_conn = container_of(work, struct iser_conn, release_work);
+
+	/* wait for .conn_stop callback */
+	wait_for_completion(&ib_conn->stop_completion);
+
+	/* wait for the qp`s post send and post receive buffers to empty */
+	wait_event_interruptible(ib_conn->wait,
+				 ib_conn->state == ISER_CONN_DOWN);
+
+	iser_conn_release(ib_conn);
+}
+
 /**
  * Frees all conn objects and deallocs conn descriptor
  */
-static void iser_conn_release(struct iser_conn *ib_conn, int can_destroy_id)
+void iser_conn_release(struct iser_conn *ib_conn)
 {
 	struct iser_device  *device = ib_conn->device;
 
-	BUG_ON(ib_conn->state != ISER_CONN_DOWN);
+	BUG_ON(ib_conn->state == ISER_CONN_UP);
 
 	mutex_lock(&ig.connlist_mutex);
 	list_del(&ib_conn->conn_list);
@@ -600,27 +616,13 @@ static void iser_conn_release(struct iser_conn *ib_conn, int can_destroy_id)
 	if (device != NULL)
 		iser_device_try_release(device);
 	/* if cma handler context, the caller actually destroy the id */
-	if (ib_conn->cma_id != NULL && can_destroy_id) {
+	if (ib_conn->cma_id != NULL) {
 		rdma_destroy_id(ib_conn->cma_id);
 		ib_conn->cma_id = NULL;
 	}
 	iscsi_destroy_endpoint(ib_conn->ep);
 }
 
-void iser_conn_get(struct iser_conn *ib_conn)
-{
-	atomic_inc(&ib_conn->refcount);
-}
-
-int iser_conn_put(struct iser_conn *ib_conn, int can_destroy_id)
-{
-	if (atomic_dec_and_test(&ib_conn->refcount)) {
-		iser_conn_release(ib_conn, can_destroy_id);
-		return 1;
-	}
-	return 0;
-}
-
 /**
  * triggers start of the disconnect procedures and wait for them to be done
  */
@@ -638,24 +640,19 @@ void iser_conn_terminate(struct iser_conn *ib_conn)
 	if (err)
 		iser_err("Failed to disconnect, conn: 0x%p err %d\n",
 			 ib_conn,err);
-
-	wait_event_interruptible(ib_conn->wait,
-				 ib_conn->state == ISER_CONN_DOWN);
-
-	iser_conn_put(ib_conn, 1); /* deref ib conn deallocate */
 }
 
-static int iser_connect_error(struct rdma_cm_id *cma_id)
+static void iser_connect_error(struct rdma_cm_id *cma_id)
 {
 	struct iser_conn *ib_conn;
+
 	ib_conn = (struct iser_conn *)cma_id->context;
 
 	ib_conn->state = ISER_CONN_DOWN;
 	wake_up_interruptible(&ib_conn->wait);
-	return iser_conn_put(ib_conn, 0); /* deref ib conn's cma id */
 }
 
-static int iser_addr_handler(struct rdma_cm_id *cma_id)
+static void iser_addr_handler(struct rdma_cm_id *cma_id)
 {
 	struct iser_device *device;
 	struct iser_conn   *ib_conn;
@@ -664,7 +661,8 @@ static int iser_addr_handler(struct rdma_cm_id *cma_id)
 	device = iser_device_find_by_ib_device(cma_id);
 	if (!device) {
 		iser_err("device lookup/creation failed\n");
-		return iser_connect_error(cma_id);
+		iser_connect_error(cma_id);
+		return;
 	}
 
 	ib_conn = (struct iser_conn *)cma_id->context;
@@ -686,13 +684,12 @@ static int iser_addr_handler(struct rdma_cm_id *cma_id)
 	ret = rdma_resolve_route(cma_id, 1000);
 	if (ret) {
 		iser_err("resolve route failed: %d\n", ret);
-		return iser_connect_error(cma_id);
+		iser_connect_error(cma_id);
+		return;
 	}
-
-	return 0;
 }
 
-static int iser_route_handler(struct rdma_cm_id *cma_id)
+static void iser_route_handler(struct rdma_cm_id *cma_id)
 {
 	struct rdma_conn_param conn_param;
 	int    ret;
@@ -720,9 +717,9 @@ static int iser_route_handler(struct rdma_cm_id *cma_id)
 		goto failure;
 	}
 
-	return 0;
+	return;
 failure:
-	return iser_connect_error(cma_id);
+	iser_connect_error(cma_id);
 }
 
 static void iser_connected_handler(struct rdma_cm_id *cma_id)
@@ -739,10 +736,9 @@ static void iser_connected_handler(struct rdma_cm_id *cma_id)
 	wake_up_interruptible(&ib_conn->wait);
 }
 
-static int iser_disconnected_handler(struct rdma_cm_id *cma_id)
+static void iser_disconnected_handler(struct rdma_cm_id *cma_id)
 {
 	struct iser_conn *ib_conn;
-	int ret;
 
 	ib_conn = (struct iser_conn *)cma_id->context;
 
@@ -762,24 +758,19 @@ static int iser_disconnected_handler(struct rdma_cm_id *cma_id)
 		ib_conn->state = ISER_CONN_DOWN;
 		wake_up_interruptible(&ib_conn->wait);
 	}
-
-	ret = iser_conn_put(ib_conn, 0); /* deref ib conn's cma id */
-	return ret;
 }
 
 static int iser_cma_handler(struct rdma_cm_id *cma_id, struct rdma_cm_event *event)
 {
-	int ret = 0;
-
 	iser_info("event %d status %d conn %p id %p\n",
 		  event->event, event->status, cma_id->context, cma_id);
 
 	switch (event->event) {
 	case RDMA_CM_EVENT_ADDR_RESOLVED:
-		ret = iser_addr_handler(cma_id);
+		iser_addr_handler(cma_id);
 		break;
 	case RDMA_CM_EVENT_ROUTE_RESOLVED:
-		ret = iser_route_handler(cma_id);
+		iser_route_handler(cma_id);
 		break;
 	case RDMA_CM_EVENT_ESTABLISHED:
 		iser_connected_handler(cma_id);
@@ -789,18 +780,18 @@ static int iser_cma_handler(struct rdma_cm_id *cma_id, struct rdma_cm_event *eve
 	case RDMA_CM_EVENT_CONNECT_ERROR:
 	case RDMA_CM_EVENT_UNREACHABLE:
 	case RDMA_CM_EVENT_REJECTED:
-		ret = iser_connect_error(cma_id);
+		iser_connect_error(cma_id);
 		break;
 	case RDMA_CM_EVENT_DISCONNECTED:
 	case RDMA_CM_EVENT_DEVICE_REMOVAL:
 	case RDMA_CM_EVENT_ADDR_CHANGE:
-		ret = iser_disconnected_handler(cma_id);
+		iser_disconnected_handler(cma_id);
 		break;
 	default:
 		iser_err("Unexpected RDMA CM event (%d)\n", event->event);
 		break;
 	}
-	return ret;
+	return 0;
 }
 
 void iser_conn_init(struct iser_conn *ib_conn)
@@ -809,7 +800,7 @@ void iser_conn_init(struct iser_conn *ib_conn)
 	init_waitqueue_head(&ib_conn->wait);
 	ib_conn->post_recv_buf_count = 0;
 	atomic_set(&ib_conn->post_send_buf_count, 0);
-	atomic_set(&ib_conn->refcount, 1); /* ref ib conn allocation */
+	init_completion(&ib_conn->stop_completion);
 	INIT_LIST_HEAD(&ib_conn->conn_list);
 	spin_lock_init(&ib_conn->lock);
 }
@@ -837,7 +828,6 @@ int iser_connect(struct iser_conn   *ib_conn,
 
 	ib_conn->state = ISER_CONN_PENDING;
 
-	iser_conn_get(ib_conn); /* ref ib conn's cma id */
 	ib_conn->cma_id = rdma_create_id(iser_cma_handler,
 					     (void *)ib_conn,
 					     RDMA_PS_TCP, IB_QPT_RC);
@@ -874,9 +864,8 @@ id_failure:
 	ib_conn->cma_id = NULL;
 addr_failure:
 	ib_conn->state = ISER_CONN_DOWN;
-	iser_conn_put(ib_conn, 1); /* deref ib conn's cma id */
 connect_failure:
-	iser_conn_put(ib_conn, 1); /* deref ib conn deallocate */
+	iser_conn_release(ib_conn);
 	return err;
 }