iser-target: Remove an atomic operation from the IO path

In order to know that we consumed all the connection completions
we maintain atomic post_send_buf_count for each IO post send. But
we can know that if we post a "beacon" (zero length RECV work request)
after we move the QP into error state and the target does not serve
any new IO. When we consume it, we know we finished all the connection
completion and we can go ahead and destroy stuff.

In error completion handler we now just need to check for ISERT_BEACON_WRID
to arrive and then wait for session commands to cleanup and complete
conn_wait_comp_err.

We reserve another CQ and QP entries to fit the zero length post recv.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/infiniband/ulp/isert/ib_isert.c

@@ -35,7 +35,8 @@
 #define	ISERT_MAX_CONN		8
 #define ISER_MAX_RX_CQ_LEN	(ISERT_QP_MAX_RECV_DTOS * ISERT_MAX_CONN)
 #define ISER_MAX_TX_CQ_LEN	(ISERT_QP_MAX_REQ_DTOS  * ISERT_MAX_CONN)
-#define ISER_MAX_CQ_LEN		(ISER_MAX_RX_CQ_LEN + ISER_MAX_TX_CQ_LEN)
+#define ISER_MAX_CQ_LEN		(ISER_MAX_RX_CQ_LEN + ISER_MAX_TX_CQ_LEN + \
+				 ISERT_MAX_CONN)
 
 static DEFINE_MUTEX(device_list_mutex);
 static LIST_HEAD(device_list);
@@ -127,7 +128,7 @@ isert_conn_setup_qp(struct isert_conn *isert_conn, struct rdma_cm_id *cma_id)
 	attr.send_cq = comp->cq;
 	attr.recv_cq = comp->cq;
 	attr.cap.max_send_wr = ISERT_QP_MAX_REQ_DTOS;
-	attr.cap.max_recv_wr = ISERT_QP_MAX_RECV_DTOS;
+	attr.cap.max_recv_wr = ISERT_QP_MAX_RECV_DTOS + 1;
 	/*
 	 * FIXME: Use devattr.max_sge - 2 for max_send_sge as
 	 * work-around for RDMA_READs with ConnectX-2.
@@ -593,7 +594,6 @@ isert_connect_request(struct rdma_cm_id *cma_id, struct rdma_cm_event *event)
 	init_completion(&isert_conn->conn_login_comp);
 	init_completion(&isert_conn->login_req_comp);
 	init_completion(&isert_conn->conn_wait);
-	init_completion(&isert_conn->conn_wait_comp_err);
 	kref_init(&isert_conn->conn_kref);
 	mutex_init(&isert_conn->conn_mutex);
 	spin_lock_init(&isert_conn->conn_lock);
@@ -811,12 +811,6 @@ isert_conn_terminate(struct isert_conn *isert_conn)
 	case ISER_CONN_TERMINATING:
 		break;
 	case ISER_CONN_UP:
-		/*
-		 * No flush completions will occur as we didn't
-		 * get to ISER_CONN_FULL_FEATURE yet, complete
-		 * to allow teardown progress.
-		 */
-		complete(&isert_conn->conn_wait_comp_err);
 	case ISER_CONN_FULL_FEATURE: /* FALLTHRU */
 		pr_info("Terminating conn %p state %d\n",
 			   isert_conn, isert_conn->state);
@@ -975,13 +969,9 @@ isert_post_send(struct isert_conn *isert_conn, struct iser_tx_desc *tx_desc)
 	send_wr.opcode	= IB_WR_SEND;
 	send_wr.send_flags = IB_SEND_SIGNALED;
 
-	atomic_inc(&isert_conn->post_send_buf_count);
-
 	ret = ib_post_send(isert_conn->conn_qp, &send_wr, &send_wr_failed);
-	if (ret) {
+	if (ret)
 		pr_err("ib_post_send() failed, ret: %d\n", ret);
-		atomic_dec(&isert_conn->post_send_buf_count);
-	}
 
 	return ret;
 }
@@ -1877,7 +1867,6 @@ isert_do_control_comp(struct work_struct *work)
 	case ISTATE_SEND_TASKMGTRSP:
 		pr_debug("Calling iscsit_tmr_post_handler >>>>>>>>>>>>>>>>>\n");
 
-		atomic_dec(&isert_conn->post_send_buf_count);
 		iscsit_tmr_post_handler(cmd, cmd->conn);
 
 		cmd->i_state = ISTATE_SENT_STATUS;
@@ -1885,7 +1874,6 @@ isert_do_control_comp(struct work_struct *work)
 		break;
 	case ISTATE_SEND_REJECT:
 		pr_debug("Got isert_do_control_comp ISTATE_SEND_REJECT: >>>\n");
-		atomic_dec(&isert_conn->post_send_buf_count);
 
 		cmd->i_state = ISTATE_SENT_STATUS;
 		isert_completion_put(&isert_cmd->tx_desc, isert_cmd, ib_dev, false);
@@ -1893,11 +1881,9 @@ isert_do_control_comp(struct work_struct *work)
 	case ISTATE_SEND_LOGOUTRSP:
 		pr_debug("Calling iscsit_logout_post_handler >>>>>>>>>>>>>>\n");
 
-		atomic_dec(&isert_conn->post_send_buf_count);
 		iscsit_logout_post_handler(cmd, cmd->conn);
 		break;
 	case ISTATE_SEND_TEXTRSP:
-		atomic_dec(&isert_conn->post_send_buf_count);
 		cmd->i_state = ISTATE_SENT_STATUS;
 		isert_completion_put(&isert_cmd->tx_desc, isert_cmd, ib_dev, false);
 		break;
@@ -1915,7 +1901,6 @@ isert_response_completion(struct iser_tx_desc *tx_desc,
 			  struct ib_device *ib_dev)
 {
 	struct iscsi_cmd *cmd = isert_cmd->iscsi_cmd;
-	struct isert_rdma_wr *wr = &isert_cmd->rdma_wr;
 
 	if (cmd->i_state == ISTATE_SEND_TASKMGTRSP ||
 	    cmd->i_state == ISTATE_SEND_LOGOUTRSP ||
@@ -1928,18 +1913,6 @@ isert_response_completion(struct iser_tx_desc *tx_desc,
 		return;
 	}
 
-	/**
-	 * If send_wr_num is 0 this means that we got
-	 * RDMA completion and we cleared it and we should
-	 * simply decrement the response post. else the
-	 * response is incorporated in send_wr_num, just
-	 * sub it.
-	 **/
-	if (wr->send_wr_num)
-		atomic_sub(wr->send_wr_num, &isert_conn->post_send_buf_count);
-	else
-		atomic_dec(&isert_conn->post_send_buf_count);
-
 	cmd->i_state = ISTATE_SENT_STATUS;
 	isert_completion_put(tx_desc, isert_cmd, ib_dev, false);
 }
@@ -1953,7 +1926,6 @@ isert_send_completion(struct iser_tx_desc *tx_desc,
 	struct isert_rdma_wr *wr;
 
 	if (!isert_cmd) {
-		atomic_dec(&isert_conn->post_send_buf_count);
 		isert_unmap_tx_desc(tx_desc, ib_dev);
 		return;
 	}
@@ -1971,13 +1943,11 @@ isert_send_completion(struct iser_tx_desc *tx_desc,
 		break;
 	case ISER_IB_RDMA_WRITE:
 		pr_debug("isert_send_completion: Got ISER_IB_RDMA_WRITE\n");
-		atomic_sub(wr->send_wr_num, &isert_conn->post_send_buf_count);
 		isert_completion_rdma_write(tx_desc, isert_cmd);
 		break;
 	case ISER_IB_RDMA_READ:
 		pr_debug("isert_send_completion: Got ISER_IB_RDMA_READ:\n");
 
-		atomic_sub(wr->send_wr_num, &isert_conn->post_send_buf_count);
 		isert_completion_rdma_read(tx_desc, isert_cmd);
 		break;
 	default:
@@ -2013,6 +1983,18 @@ is_isert_tx_desc(struct isert_conn *isert_conn, void *wr_id)
 static void
 isert_cq_comp_err(struct isert_conn *isert_conn, struct ib_wc *wc)
 {
+	if (wc->wr_id == ISER_BEACON_WRID) {
+		struct iscsi_conn *conn = isert_conn->conn;
+
+		if (conn->sess) {
+			target_sess_cmd_list_set_waiting(conn->sess->se_sess);
+			target_wait_for_sess_cmds(conn->sess->se_sess);
+		}
+
+		pr_info("conn %p completing conn_wait_comp_err\n",
+			   isert_conn);
+		complete(&isert_conn->conn_wait_comp_err);
+	} else
 	if (is_isert_tx_desc(isert_conn, (void *)wc->wr_id)) {
 		struct ib_device *ib_dev = isert_conn->conn_cm_id->device;
 		struct isert_cmd *isert_cmd;
@@ -2024,22 +2006,10 @@ isert_cq_comp_err(struct isert_conn *isert_conn, struct ib_wc *wc)
 			isert_unmap_tx_desc(desc, ib_dev);
 		else
 			isert_completion_put(desc, isert_cmd, ib_dev, true);
-		atomic_dec(&isert_conn->post_send_buf_count);
 	} else {
 		isert_conn->post_recv_buf_count--;
-	}
-
-	if (isert_conn->post_recv_buf_count == 0 &&
-	    atomic_read(&isert_conn->post_send_buf_count) == 0) {
-		struct iscsi_conn *conn = isert_conn->conn;
-
-		if (conn->sess) {
-			target_sess_cmd_list_set_waiting(conn->sess->se_sess);
-			target_wait_for_sess_cmds(conn->sess->se_sess);
-		}
-
-		iscsit_cause_connection_reinstatement(isert_conn->conn, 0);
-		complete(&isert_conn->conn_wait_comp_err);
+		if (!isert_conn->post_recv_buf_count)
+			iscsit_cause_connection_reinstatement(isert_conn->conn, 0);
 	}
 }
 
@@ -2098,13 +2068,10 @@ isert_post_response(struct isert_conn *isert_conn, struct isert_cmd *isert_cmd)
 	struct ib_send_wr *wr_failed;
 	int ret;
 
-	atomic_inc(&isert_conn->post_send_buf_count);
-
 	ret = ib_post_send(isert_conn->conn_qp, &isert_cmd->tx_desc.send_wr,
 			   &wr_failed);
 	if (ret) {
 		pr_err("ib_post_send failed with %d\n", ret);
-		atomic_dec(&isert_conn->post_send_buf_count);
 		return ret;
 	}
 	return ret;
@@ -2889,13 +2856,9 @@ isert_put_datain(struct iscsi_conn *conn, struct iscsi_cmd *cmd)
 		wr->send_wr_num += 1;
 	}
 
-	atomic_add(wr->send_wr_num, &isert_conn->post_send_buf_count);
-
 	rc = ib_post_send(isert_conn->conn_qp, wr->send_wr, &wr_failed);
-	if (rc) {
+	if (rc)
 		pr_warn("ib_post_send() failed for IB_WR_RDMA_WRITE\n");
-		atomic_sub(wr->send_wr_num, &isert_conn->post_send_buf_count);
-	}
 
 	if (!isert_prot_cmd(isert_conn, se_cmd))
 		pr_debug("Cmd: %p posted RDMA_WRITE + Response for iSER Data "
@@ -2927,13 +2890,10 @@ isert_get_dataout(struct iscsi_conn *conn, struct iscsi_cmd *cmd, bool recovery)
 		return rc;
 	}
 
-	atomic_add(wr->send_wr_num, &isert_conn->post_send_buf_count);
-
 	rc = ib_post_send(isert_conn->conn_qp, wr->send_wr, &wr_failed);
-	if (rc) {
+	if (rc)
 		pr_warn("ib_post_send() failed for IB_WR_RDMA_READ\n");
-		atomic_sub(wr->send_wr_num, &isert_conn->post_send_buf_count);
-	}
+
 	pr_debug("Cmd: %p posted RDMA_READ memory for ISER Data WRITE\n",
 		 isert_cmd);
 
@@ -3274,6 +3234,22 @@ static void isert_release_work(struct work_struct *work)
 	isert_put_conn(isert_conn);
 }
 
+static void
+isert_wait4flush(struct isert_conn *isert_conn)
+{
+	struct ib_recv_wr *bad_wr;
+
+	init_completion(&isert_conn->conn_wait_comp_err);
+	isert_conn->beacon.wr_id = ISER_BEACON_WRID;
+	/* post an indication that all flush errors were consumed */
+	if (ib_post_recv(isert_conn->conn_qp, &isert_conn->beacon, &bad_wr)) {
+		pr_err("conn %p failed to post beacon", isert_conn);
+		return;
+	}
+
+	wait_for_completion(&isert_conn->conn_wait_comp_err);
+}
+
 static void isert_wait_conn(struct iscsi_conn *conn)
 {
 	struct isert_conn *isert_conn = conn->context;
@@ -3292,7 +3268,7 @@ static void isert_wait_conn(struct iscsi_conn *conn)
 	isert_conn_terminate(isert_conn);
 	mutex_unlock(&isert_conn->conn_mutex);
 
-	wait_for_completion(&isert_conn->conn_wait_comp_err);
+	isert_wait4flush(isert_conn);
 
 	INIT_WORK(&isert_conn->release_work, isert_release_work);
 	queue_work(isert_release_wq, &isert_conn->release_work);

drivers/infiniband/ulp/isert/ib_isert.h

@@ -7,6 +7,7 @@
 #define ISERT_RDMA_LISTEN_BACKLOG	10
 #define ISCSI_ISER_SG_TABLESIZE		256
 #define ISER_FASTREG_LI_WRID		0xffffffffffffffffULL
+#define ISER_BEACON_WRID               0xfffffffffffffffeULL
 
 enum isert_desc_type {
 	ISCSI_TX_CONTROL,
@@ -122,7 +123,6 @@ struct isert_device;
 struct isert_conn {
 	enum iser_conn_state	state;
 	int			post_recv_buf_count;
-	atomic_t		post_send_buf_count;
 	u32			responder_resources;
 	u32			initiator_depth;
 	bool			pi_support;
@@ -155,6 +155,7 @@ struct isert_conn {
 	/* lock to protect fastreg pool */
 	spinlock_t		conn_lock;
 	struct work_struct	release_work;
+	struct ib_recv_wr       beacon;
 };
 
 #define ISERT_MAX_CQ 64