scsi: libiscsi: Drop taskqueuelock

The purpose of the taskqueuelock was to handle the issue where a bad target
decides to send a R2T and before its data has been sent decides to send a
cmd response to complete the cmd. The following patches fix up the
frwd/back locks so they are taken from the queue/xmit (frwd) and completion
(back) paths again. To get there this patch removes the taskqueuelock which
for iSCSI xmit wq based drivers was taken in the queue, xmit and completion
paths.

Instead of the lock, we just make sure we have a ref to the task when we
queue a R2T, and then we always remove the task from the requeue list in
the xmit path or the forced cleanup paths.

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Lee Duncan <[e-mail]>
Signed-off-by: Mike Christie <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/libiscsi.c

···
 	WARN_ON_ONCE(task->state == ISCSI_TASK_FREE);
 	task->state = state;
 
-	spin_lock_bh(&conn->taskqueuelock);
-	if (!list_empty(&task->running)) {
-		pr_debug_once("%s while task on list", __func__);
-		list_del_init(&task->running);
-	}
-	spin_unlock_bh(&conn->taskqueuelock);
-
-	if (conn->task == task)
-		conn->task = NULL;
-
 	if (READ_ONCE(conn->ping_task) == task)
 		WRITE_ONCE(conn->ping_task, NULL);
 
···
 }
 EXPORT_SYMBOL_GPL(iscsi_complete_scsi_task);
 
+/*
+ * Must be called with back and frwd lock
+ */
+static bool cleanup_queued_task(struct iscsi_task *task)
+{
+	struct iscsi_conn *conn = task->conn;
+	bool early_complete = false;
+
+	/* Bad target might have completed task while it was still running */
+	if (task->state == ISCSI_TASK_COMPLETED)
+		early_complete = true;
+
+	if (!list_empty(&task->running)) {
+		list_del_init(&task->running);
+		/*
+		 * If it's on a list but still running, this could be from
+		 * a bad target sending a rsp early, cleanup from a TMF, or
+		 * session recovery.
+		 */
+		if (task->state == ISCSI_TASK_RUNNING ||
+		    task->state == ISCSI_TASK_COMPLETED)
+			__iscsi_put_task(task);
+	}
+
+	if (conn->task == task) {
+		conn->task = NULL;
+		__iscsi_put_task(task);
+	}
+
+	return early_complete;
+}
 
 /*
- * session back_lock must be held and if not called for a task that is
+ * session frwd_lock must be held and if not called for a task that is
  * still pending or from the xmit thread, then xmit thread must
  * be suspended.
  */
···
 	if (!sc)
 		return;
 
+	/* regular RX path uses back_lock */
+	spin_lock_bh(&conn->session->back_lock);
+	if (cleanup_queued_task(task)) {
+		spin_unlock_bh(&conn->session->back_lock);
+		return;
+	}
+
 	if (task->state == ISCSI_TASK_PENDING) {
 		/*
 		 * cmd never made it to the xmit thread, so we should not count
···
 
 	sc->result = err << 16;
 	scsi_set_resid(sc, scsi_bufflen(sc));
-
-	/* regular RX path uses back_lock */
-	spin_lock_bh(&conn->session->back_lock);
 	iscsi_complete_task(task, state);
 	spin_unlock_bh(&conn->session->back_lock);
 }
···
 		if (session->tt->xmit_task(task))
 			goto free_task;
 	} else {
-		spin_lock_bh(&conn->taskqueuelock);
 		list_add_tail(&task->running, &conn->mgmtqueue);
-		spin_unlock_bh(&conn->taskqueuelock);
 		iscsi_conn_queue_work(conn);
 	}
 
···
 	return 0;
 }
 
-static int iscsi_xmit_task(struct iscsi_conn *conn)
+static int iscsi_xmit_task(struct iscsi_conn *conn, struct iscsi_task *task,
+			   bool was_requeue)
 {
-	struct iscsi_task *task = conn->task;
 	int rc;
 
-	if (test_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx))
-		return -ENODATA;
-
 	spin_lock_bh(&conn->session->back_lock);
-	if (conn->task == NULL) {
+
+	if (!conn->task) {
+		/* Take a ref so we can access it after xmit_task() */
+		__iscsi_get_task(task);
+	} else {
+		/* Already have a ref from when we failed to send it last call */
+		conn->task = NULL;
+	}
+
+	/*
+	 * If this was a requeue for a R2T we have an extra ref on the task in
+	 * case a bad target sends a cmd rsp before we have handled the task.
+	 */
+	if (was_requeue)
+		__iscsi_put_task(task);
+
+	/*
+	 * Do this after dropping the extra ref because if this was a requeue
+	 * it's removed from that list and cleanup_queued_task would miss it.
+	 */
+	if (test_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx)) {
+		/*
+		 * Save the task and ref in case we weren't cleaning up this
+		 * task and get woken up again.
+		 */
+		conn->task = task;
 		spin_unlock_bh(&conn->session->back_lock);
 		return -ENODATA;
 	}
-	__iscsi_get_task(task);
 	spin_unlock_bh(&conn->session->back_lock);
+
 	spin_unlock_bh(&conn->session->frwd_lock);
 	rc = conn->session->tt->xmit_task(task);
 	spin_lock_bh(&conn->session->frwd_lock);
 	if (!rc) {
 		/* done with this task */
 		task->last_xfer = jiffies;
-		conn->task = NULL;
 	}
 	/* regular RX path uses back_lock */
 	spin_lock(&conn->session->back_lock);
+	if (rc && task->state == ISCSI_TASK_RUNNING) {
+		/*
+		 * get an extra ref that is released next time we access it
+		 * as conn->task above.
+		 */
+		__iscsi_get_task(task);
+		conn->task = task;
+	}
+
 	__iscsi_put_task(task);
 	spin_unlock(&conn->session->back_lock);
 	return rc;
···
  * iscsi_requeue_task - requeue task to run from session workqueue
  * @task: task to requeue
  *
- * LLDs that need to run a task from the session workqueue should call
- * this. The session frwd_lock must be held. This should only be called
- * by software drivers.
+ * Callers must have taken a ref to the task that is going to be requeued.
  */
 void iscsi_requeue_task(struct iscsi_task *task)
 {
···
 	 * this may be on the requeue list already if the xmit_task callout
 	 * is handling the r2ts while we are adding new ones
 	 */
-	spin_lock_bh(&conn->taskqueuelock);
-	if (list_empty(&task->running))
+	spin_lock_bh(&conn->session->frwd_lock);
+	if (list_empty(&task->running)) {
 		list_add_tail(&task->running, &conn->requeue);
-	spin_unlock_bh(&conn->taskqueuelock);
+	} else {
+		/*
+		 * Don't need the extra ref since it's already requeued and
+		 * has a ref.
+		 */
+		iscsi_put_task(task);
+	}
 	iscsi_conn_queue_work(conn);
+	spin_unlock_bh(&conn->session->frwd_lock);
 }
 EXPORT_SYMBOL_GPL(iscsi_requeue_task);
 
···
 	}
 
 	if (conn->task) {
-		rc = iscsi_xmit_task(conn);
+		rc = iscsi_xmit_task(conn, conn->task, false);
 	        if (rc)
 		        goto done;
 	}
···
 	 * only have one nop-out as a ping from us and targets should not
 	 * overflow us with nop-ins
 	 */
-	spin_lock_bh(&conn->taskqueuelock);
 check_mgmt:
 	while (!list_empty(&conn->mgmtqueue)) {
-		conn->task = list_entry(conn->mgmtqueue.next,
-					 struct iscsi_task, running);
-		list_del_init(&conn->task->running);
-		spin_unlock_bh(&conn->taskqueuelock);
-		if (iscsi_prep_mgmt_task(conn, conn->task)) {
+		task = list_entry(conn->mgmtqueue.next, struct iscsi_task,
+				  running);
+		list_del_init(&task->running);
+		if (iscsi_prep_mgmt_task(conn, task)) {
 			/* regular RX path uses back_lock */
 			spin_lock_bh(&conn->session->back_lock);
-			__iscsi_put_task(conn->task);
+			__iscsi_put_task(task);
 			spin_unlock_bh(&conn->session->back_lock);
-			conn->task = NULL;
-			spin_lock_bh(&conn->taskqueuelock);
 			continue;
 		}
-		rc = iscsi_xmit_task(conn);
+		rc = iscsi_xmit_task(conn, task, false);
 		if (rc)
 			goto done;
-		spin_lock_bh(&conn->taskqueuelock);
 	}
 
 	/* process pending command queue */
 	while (!list_empty(&conn->cmdqueue)) {
-		conn->task = list_entry(conn->cmdqueue.next, struct iscsi_task,
-					running);
-		list_del_init(&conn->task->running);
-		spin_unlock_bh(&conn->taskqueuelock);
+		task = list_entry(conn->cmdqueue.next, struct iscsi_task,
+				  running);
+		list_del_init(&task->running);
 		if (conn->session->state == ISCSI_STATE_LOGGING_OUT) {
-			fail_scsi_task(conn->task, DID_IMM_RETRY);
-			spin_lock_bh(&conn->taskqueuelock);
+			fail_scsi_task(task, DID_IMM_RETRY);
 			continue;
 		}
-		rc = iscsi_prep_scsi_cmd_pdu(conn->task);
+		rc = iscsi_prep_scsi_cmd_pdu(task);
 		if (rc) {
 			if (rc == -ENOMEM || rc == -EACCES)
-				fail_scsi_task(conn->task, DID_IMM_RETRY);
+				fail_scsi_task(task, DID_IMM_RETRY);
 			else
-				fail_scsi_task(conn->task, DID_ABORT);
-			spin_lock_bh(&conn->taskqueuelock);
+				fail_scsi_task(task, DID_ABORT);
 			continue;
 		}
-		rc = iscsi_xmit_task(conn);
+		rc = iscsi_xmit_task(conn, task, false);
 		if (rc)
 			goto done;
 		/*
···
 		 * we need to check the mgmt queue for nops that need to
 		 * be sent to aviod starvation
 		 */
-		spin_lock_bh(&conn->taskqueuelock);
 		if (!list_empty(&conn->mgmtqueue))
 			goto check_mgmt;
 	}
···
 
 		task = list_entry(conn->requeue.next, struct iscsi_task,
 				  running);
+
 		if (iscsi_check_tmf_restrictions(task, ISCSI_OP_SCSI_DATA_OUT))
 			break;
 
-		conn->task = task;
-		list_del_init(&conn->task->running);
-		conn->task->state = ISCSI_TASK_RUNNING;
-		spin_unlock_bh(&conn->taskqueuelock);
-		rc = iscsi_xmit_task(conn);
+		list_del_init(&task->running);
+		rc = iscsi_xmit_task(conn, task, true);
 		if (rc)
 			goto done;
-		spin_lock_bh(&conn->taskqueuelock);
 		if (!list_empty(&conn->mgmtqueue))
 			goto check_mgmt;
 	}
-	spin_unlock_bh(&conn->taskqueuelock);
 	spin_unlock_bh(&conn->session->frwd_lock);
 	return -ENODATA;
 
···
 			goto prepd_reject;
 		}
 	} else {
-		spin_lock_bh(&conn->taskqueuelock);
 		list_add_tail(&task->running, &conn->cmdqueue);
-		spin_unlock_bh(&conn->taskqueuelock);
 		iscsi_conn_queue_work(conn);
 	}
 
···
 	INIT_LIST_HEAD(&conn->mgmtqueue);
 	INIT_LIST_HEAD(&conn->cmdqueue);
 	INIT_LIST_HEAD(&conn->requeue);
-	spin_lock_init(&conn->taskqueuelock);
 	INIT_WORK(&conn->xmitwork, iscsi_xmitworker);
 
 	/* allocate login_task used for the login/text sequences */
···
 		ISCSI_DBG_SESSION(conn->session,
 				  "failing mgmt itt 0x%x state %d\n",
 				  task->itt, task->state);
+
+		spin_lock_bh(&session->back_lock);
+		if (cleanup_queued_task(task)) {
+			spin_unlock_bh(&session->back_lock);
+			continue;
+		}
+
 		state = ISCSI_TASK_ABRT_SESS_RECOV;
 		if (task->state == ISCSI_TASK_PENDING)
 			state = ISCSI_TASK_COMPLETED;
-		spin_lock_bh(&session->back_lock);
 		iscsi_complete_task(task, state);
 		spin_unlock_bh(&session->back_lock);
 	}

drivers/scsi/libiscsi_tcp.c

···
 /**
  * iscsi_tcp_r2t_rsp - iSCSI R2T Response processing
  * @conn: iscsi connection
- * @task: scsi command task
+ * @hdr: PDU header
  */
-static int iscsi_tcp_r2t_rsp(struct iscsi_conn *conn, struct iscsi_task *task)
+static int iscsi_tcp_r2t_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr)
 {
 	struct iscsi_session *session = conn->session;
-	struct iscsi_tcp_task *tcp_task = task->dd_data;
-	struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
-	struct iscsi_r2t_rsp *rhdr = (struct iscsi_r2t_rsp *)tcp_conn->in.hdr;
+	struct iscsi_tcp_task *tcp_task;
+	struct iscsi_tcp_conn *tcp_conn;
+	struct iscsi_r2t_rsp *rhdr;
 	struct iscsi_r2t_info *r2t;
-	int r2tsn = be32_to_cpu(rhdr->r2tsn);
+	struct iscsi_task *task;
 	u32 data_length;
 	u32 data_offset;
+	int r2tsn;
 	int rc;
+
+	spin_lock(&session->back_lock);
+	task = iscsi_itt_to_ctask(conn, hdr->itt);
+	if (!task) {
+		spin_unlock(&session->back_lock);
+		return ISCSI_ERR_BAD_ITT;
+	} else if (task->sc->sc_data_direction != DMA_TO_DEVICE) {
+		spin_unlock(&session->back_lock);
+		return ISCSI_ERR_PROTO;
+	}
+	/*
+	 * A bad target might complete the cmd before we have handled R2Ts
+	 * so get a ref to the task that will be dropped in the xmit path.
+	 */
+	if (task->state != ISCSI_TASK_RUNNING) {
+		spin_unlock(&session->back_lock);
+		/* Let the path that got the early rsp complete it */
+		return 0;
+	}
+	task->last_xfer = jiffies;
+	__iscsi_get_task(task);
+
+	tcp_conn = conn->dd_data;
+	rhdr = (struct iscsi_r2t_rsp *)tcp_conn->in.hdr;
+	/* fill-in new R2T associated with the task */
+	iscsi_update_cmdsn(session, (struct iscsi_nopin *)rhdr);
+	spin_unlock(&session->back_lock);
 
 	if (tcp_conn->in.datalen) {
 		iscsi_conn_printk(KERN_ERR, conn,
 				  "invalid R2t with datalen %d\n",
 				  tcp_conn->in.datalen);
-		return ISCSI_ERR_DATALEN;
+		rc = ISCSI_ERR_DATALEN;
+		goto put_task;
 	}
 
+	tcp_task = task->dd_data;
+	r2tsn = be32_to_cpu(rhdr->r2tsn);
 	if (tcp_task->exp_datasn != r2tsn){
 		ISCSI_DBG_TCP(conn, "task->exp_datasn(%d) != rhdr->r2tsn(%d)\n",
 			      tcp_task->exp_datasn, r2tsn);
-		return ISCSI_ERR_R2TSN;
+		rc = ISCSI_ERR_R2TSN;
+		goto put_task;
 	}
 
-	/* fill-in new R2T associated with the task */
-	iscsi_update_cmdsn(session, (struct iscsi_nopin*)rhdr);
-
-	if (!task->sc || session->state != ISCSI_STATE_LOGGED_IN) {
+	if (session->state != ISCSI_STATE_LOGGED_IN) {
 		iscsi_conn_printk(KERN_INFO, conn,
 				  "dropping R2T itt %d in recovery.\n",
 				  task->itt);
-		return 0;
+		rc = 0;
+		goto put_task;
 	}
 
 	data_length = be32_to_cpu(rhdr->data_length);
 	if (data_length == 0) {
 		iscsi_conn_printk(KERN_ERR, conn,
 				  "invalid R2T with zero data len\n");
-		return ISCSI_ERR_DATALEN;
+		rc = ISCSI_ERR_DATALEN;
+		goto put_task;
 	}
 
 	if (data_length > session->max_burst)
···
 				  "invalid R2T with data len %u at offset %u "
 				  "and total length %d\n", data_length,
 				  data_offset, task->sc->sdb.length);
-		return ISCSI_ERR_DATALEN;
+		rc = ISCSI_ERR_DATALEN;
+		goto put_task;
 	}
 
 	spin_lock(&tcp_task->pool2queue);
···
 				  "Target has sent more R2Ts than it "
 				  "negotiated for or driver has leaked.\n");
 		spin_unlock(&tcp_task->pool2queue);
-		return ISCSI_ERR_PROTO;
+		rc = ISCSI_ERR_PROTO;
+		goto put_task;
 	}
 
 	r2t->exp_statsn = rhdr->statsn;
···
 
 	iscsi_requeue_task(task);
 	return 0;
+
+put_task:
+	iscsi_put_task(task);
+	return rc;
 }
 
 /*
···
 		rc = iscsi_complete_pdu(conn, hdr, NULL, 0);
 		break;
 	case ISCSI_OP_R2T:
-		spin_lock(&conn->session->back_lock);
-		task = iscsi_itt_to_ctask(conn, hdr->itt);
-		spin_unlock(&conn->session->back_lock);
-		if (!task)
-			rc = ISCSI_ERR_BAD_ITT;
-		else if (ahslen)
+		if (ahslen) {
 			rc = ISCSI_ERR_AHSLEN;
-		else if (task->sc->sc_data_direction == DMA_TO_DEVICE) {
-			task->last_xfer = jiffies;
-			spin_lock(&conn->session->frwd_lock);
-			rc = iscsi_tcp_r2t_rsp(conn, task);
-			spin_unlock(&conn->session->frwd_lock);
-		} else
-			rc = ISCSI_ERR_PROTO;
+			break;
+		}
+		rc = iscsi_tcp_r2t_rsp(conn, hdr);
 		break;
 	case ISCSI_OP_LOGIN_RSP:
 	case ISCSI_OP_TEXT_RSP:

include/scsi/libiscsi.h

···
 	struct iscsi_task	*task;		/* xmit task in progress */
 
 	/* xmit */
-	spinlock_t		taskqueuelock;  /* protects the next three lists */
+	/* items must be added/deleted under frwd lock */
 	struct list_head	mgmtqueue;	/* mgmt (control) xmit queue */
 	struct list_head	cmdqueue;	/* data-path cmd queue */
 	struct list_head	requeue;	/* tasks needing another run */
···
 						 * cmdsn, queued_cmdsn     *
 						 * session resources:      *
 						 * - cmdpool kfifo_out ,   *
-						 * - mgmtpool,		   */
+						 * - mgmtpool, queues	   */
 	spinlock_t		back_lock;	/* protects cmdsn_exp      *
 						 * cmdsn_max,              *
 						 * cmdpool kfifo_in        */