scsi: libiscsi: Improve conn_send_pdu API

The conn_send_pdu API is evil in that it returns a pointer to an
iscsi_task, but that task might have been freed already so you can't touch
it. This patch splits the task allocation and transmission, so functions
like iscsi_send_nopout() can access the task before its sent and do
whatever bookkeeping is needed before it is sent.

Link: https://lore.kernel.org/r/20220616224557.115234-10-michael.christie@oracle.comReviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/libiscsi.c

@@ -695,12 +695,18 @@ static int iscsi_prep_mgmt_task(struct iscsi_conn *conn,
 	return 0;
 }
 
+/**
+ * iscsi_alloc_mgmt_task - allocate and setup a mgmt task.
+ * @conn: iscsi conn that the task will be sent on.
+ * @hdr: iscsi pdu that will be sent.
+ * @data: buffer for data segment if needed.
+ * @data_size: length of data in bytes.
+ */
 static struct iscsi_task *
-__iscsi_conn_send_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
+iscsi_alloc_mgmt_task(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
 		      char *data, uint32_t data_size)
 {
 	struct iscsi_session *session = conn->session;
-	struct iscsi_host *ihost = shost_priv(session->host);
 	uint8_t opcode = hdr->opcode & ISCSI_OPCODE_MASK;
 	struct iscsi_task *task;
 	itt_t itt;
@@ -781,28 +787,57 @@ __iscsi_conn_send_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
 						   task->conn->session->age);
 	}
 
-	if (unlikely(READ_ONCE(conn->ping_task) == INVALID_SCSI_TASK))
-		WRITE_ONCE(conn->ping_task, task);
+	return task;
+
+free_task:
+	iscsi_put_task(task);
+	return NULL;
+}
+
+/**
+ * iscsi_send_mgmt_task - Send task created with iscsi_alloc_mgmt_task.
+ * @task: iscsi task to send.
+ *
+ * On failure this returns a non-zero error code, and the driver must free
+ * the task with iscsi_put_task;
+ */
+static int iscsi_send_mgmt_task(struct iscsi_task *task)
+{
+	struct iscsi_conn *conn = task->conn;
+	struct iscsi_session *session = conn->session;
+	struct iscsi_host *ihost = shost_priv(conn->session->host);
+	int rc = 0;
 
 	if (!ihost->workq) {
-		if (iscsi_prep_mgmt_task(conn, task))
-			goto free_task;
+		rc = iscsi_prep_mgmt_task(conn, task);
+		if (rc)
+			return rc;
 
-		if (session->tt->xmit_task(task))
-			goto free_task;
+		rc = session->tt->xmit_task(task);
+		if (rc)
+			return rc;
 	} else {
 		list_add_tail(&task->running, &conn->mgmtqueue);
 		iscsi_conn_queue_xmit(conn);
 	}
 
-	return task;
+	return 0;
+}
 
-free_task:
-	/* regular RX path uses back_lock */
-	spin_lock(&session->back_lock);
-	__iscsi_put_task(task);
-	spin_unlock(&session->back_lock);
-	return NULL;
+static int __iscsi_conn_send_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
+				 char *data, uint32_t data_size)
+{
+	struct iscsi_task *task;
+	int rc;
+
+	task = iscsi_alloc_mgmt_task(conn, hdr, data, data_size);
+	if (!task)
+		return -ENOMEM;
+
+	rc = iscsi_send_mgmt_task(task);
+	if (rc)
+		iscsi_put_task(task);
+	return rc;
 }
 
 int iscsi_conn_send_pdu(struct iscsi_cls_conn *cls_conn, struct iscsi_hdr *hdr,
@@ -813,7 +848,7 @@ int iscsi_conn_send_pdu(struct iscsi_cls_conn *cls_conn, struct iscsi_hdr *hdr,
 	int err = 0;
 
 	spin_lock_bh(&session->frwd_lock);
-	if (!__iscsi_conn_send_pdu(conn, hdr, data, data_size))
+	if (__iscsi_conn_send_pdu(conn, hdr, data, data_size))
 		err = -EPERM;
 	spin_unlock_bh(&session->frwd_lock);
 	return err;
@@ -986,7 +1021,6 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)
 	if (!rhdr) {
 		if (READ_ONCE(conn->ping_task))
 			return -EINVAL;
-		WRITE_ONCE(conn->ping_task, INVALID_SCSI_TASK);
 	}
 
 	memset(&hdr, 0, sizeof(struct iscsi_nopout));
@@ -1000,10 +1034,18 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)
 	} else
 		hdr.ttt = RESERVED_ITT;
 
-	task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)&hdr, NULL, 0);
-	if (!task) {
+	task = iscsi_alloc_mgmt_task(conn, (struct iscsi_hdr *)&hdr, NULL, 0);
+	if (!task)
+		return -ENOMEM;
+
+	if (!rhdr)
+		WRITE_ONCE(conn->ping_task, task);
+
+	if (iscsi_send_mgmt_task(task)) {
 		if (!rhdr)
 			WRITE_ONCE(conn->ping_task, NULL);
+		iscsi_put_task(task);
+
 		iscsi_conn_printk(KERN_ERR, conn, "Could not send nopout\n");
 		return -EIO;
 	} else if (!rhdr) {
@@ -1874,11 +1916,8 @@ static int iscsi_exec_task_mgmt_fn(struct iscsi_conn *conn,
 	__must_hold(&session->frwd_lock)
 {
 	struct iscsi_session *session = conn->session;
-	struct iscsi_task *task;
 
-	task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)hdr,
-				      NULL, 0);
-	if (!task) {
+	if (__iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)hdr, NULL, 0)) {
 		spin_unlock_bh(&session->frwd_lock);
 		iscsi_conn_printk(KERN_ERR, conn, "Could not send TMF.\n");
 		iscsi_conn_failure(conn, ISCSI_ERR_CONN_FAILED);

include/scsi/libiscsi.h

@@ -135,9 +135,6 @@ struct iscsi_task {
 	void			*dd_data;	/* driver/transport data */
 };
 
-/* invalid scsi_task pointer */
-#define	INVALID_SCSI_TASK	(struct iscsi_task *)-1l
-
 static inline int iscsi_task_has_unsol_data(struct iscsi_task *task)
 {
 	return task->unsol_r2t.data_length > task->unsol_r2t.sent;