target: replace the processing thread with a TMR work queue

The last functionality of the target processing thread is offloading possibly
long running task management requests from the submitter context.  To keep
TMR semantics the same we need a single threaded ordered queue, which can
be provided by a per-device workqueue with the right flags.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_device.c

@@ -715,7 +715,7 @@ void se_release_device_for_hba(struct se_device *dev)
 		se_dev_stop(dev);
 
 	if (dev->dev_ptr) {
-		kthread_stop(dev->process_thread);
+		destroy_workqueue(dev->tmr_wq);
 		if (dev->transport->free_device)
 			dev->transport->free_device(dev->dev_ptr);
 	}

drivers/target/target_core_tmr.c

@@ -351,57 +351,6 @@ static void core_tmr_drain_state_list(
 	}
 }
 
-static void core_tmr_drain_cmd_list(
-	struct se_device *dev,
-	struct se_cmd *prout_cmd,
-	struct se_node_acl *tmr_nacl,
-	int tas,
-	struct list_head *preempt_and_abort_list)
-{
-	LIST_HEAD(drain_cmd_list);
-	struct se_queue_obj *qobj = &dev->dev_queue_obj;
-	struct se_cmd *cmd, *tcmd;
-	unsigned long flags;
-
-	/*
-	 * Release all commands remaining in the per-device command queue.
-	 *
-	 * This follows the same logic as above for the state list.
-	 */
-	spin_lock_irqsave(&qobj->cmd_queue_lock, flags);
-	list_for_each_entry_safe(cmd, tcmd, &qobj->qobj_list, se_queue_node) {
-		/*
-		 * For PREEMPT_AND_ABORT usage, only process commands
-		 * with a matching reservation key.
-		 */
-		if (target_check_cdb_and_preempt(preempt_and_abort_list, cmd))
-			continue;
-		/*
-		 * Not aborting PROUT PREEMPT_AND_ABORT CDB..
-		 */
-		if (prout_cmd == cmd)
-			continue;
-
-		cmd->transport_state &= ~CMD_T_QUEUED;
-		atomic_dec(&qobj->queue_cnt);
-		list_move_tail(&cmd->se_queue_node, &drain_cmd_list);
-	}
-	spin_unlock_irqrestore(&qobj->cmd_queue_lock, flags);
-
-	while (!list_empty(&drain_cmd_list)) {
-		cmd = list_entry(drain_cmd_list.next, struct se_cmd, se_queue_node);
-		list_del_init(&cmd->se_queue_node);
-
-		pr_debug("LUN_RESET: %s from Device Queue: cmd: %p t_state:"
-			" %d t_fe_count: %d\n", (preempt_and_abort_list) ?
-			"Preempt" : "", cmd, cmd->t_state,
-			atomic_read(&cmd->t_fe_count));
-
-		core_tmr_handle_tas_abort(tmr_nacl, cmd, tas,
-				atomic_read(&cmd->t_fe_count));
-	}
-}
-
 int core_tmr_lun_reset(
         struct se_device *dev,
         struct se_tmr_req *tmr,
@@ -444,8 +393,7 @@ int core_tmr_lun_reset(
 	core_tmr_drain_tmr_list(dev, tmr, preempt_and_abort_list);
 	core_tmr_drain_state_list(dev, prout_cmd, tmr_nacl, tas,
 				preempt_and_abort_list);
-	core_tmr_drain_cmd_list(dev, prout_cmd, tmr_nacl, tas,
-				preempt_and_abort_list);
+
 	/*
 	 * Clear any legacy SPC-2 reservation when called during
 	 * LOGICAL UNIT RESET

drivers/target/target_core_transport.c

@@ -66,13 +66,11 @@ struct kmem_cache *t10_alua_lu_gp_mem_cache;
 struct kmem_cache *t10_alua_tg_pt_gp_cache;
 struct kmem_cache *t10_alua_tg_pt_gp_mem_cache;
 
-static int transport_processing_thread(void *param);
 static void transport_complete_task_attr(struct se_cmd *cmd);
 static void transport_handle_queue_full(struct se_cmd *cmd,
 		struct se_device *dev);
 static int transport_generic_get_mem(struct se_cmd *cmd);
 static void transport_put_cmd(struct se_cmd *cmd);
-static void transport_remove_cmd_from_queue(struct se_cmd *cmd);
 static int transport_set_sense_codes(struct se_cmd *cmd, u8 asc, u8 ascq);
 static void target_complete_ok_work(struct work_struct *work);
 
@@ -193,14 +191,6 @@ u32 scsi_get_new_index(scsi_index_t type)
 	return new_index;
 }
 
-static void transport_init_queue_obj(struct se_queue_obj *qobj)
-{
-	atomic_set(&qobj->queue_cnt, 0);
-	INIT_LIST_HEAD(&qobj->qobj_list);
-	init_waitqueue_head(&qobj->thread_wq);
-	spin_lock_init(&qobj->cmd_queue_lock);
-}
-
 void transport_subsystem_check_init(void)
 {
 	int ret;
@@ -566,79 +556,8 @@ void transport_cmd_finish_abort(struct se_cmd *cmd, int remove)
 
 	if (transport_cmd_check_stop_to_fabric(cmd))
 		return;
-	if (remove) {
-		transport_remove_cmd_from_queue(cmd);
+	if (remove)
 		transport_put_cmd(cmd);
-	}
-}
-
-static void transport_add_cmd_to_queue(struct se_cmd *cmd, int t_state,
-		bool at_head)
-{
-	struct se_device *dev = cmd->se_dev;
-	struct se_queue_obj *qobj = &dev->dev_queue_obj;
-	unsigned long flags;
-
-	if (t_state) {
-		spin_lock_irqsave(&cmd->t_state_lock, flags);
-		cmd->t_state = t_state;
-		cmd->transport_state |= CMD_T_ACTIVE;
-		spin_unlock_irqrestore(&cmd->t_state_lock, flags);
-	}
-
-	spin_lock_irqsave(&qobj->cmd_queue_lock, flags);
-
-	/* If the cmd is already on the list, remove it before we add it */
-	if (!list_empty(&cmd->se_queue_node))
-		list_del(&cmd->se_queue_node);
-	else
-		atomic_inc(&qobj->queue_cnt);
-
-	if (at_head)
-		list_add(&cmd->se_queue_node, &qobj->qobj_list);
-	else
-		list_add_tail(&cmd->se_queue_node, &qobj->qobj_list);
-	cmd->transport_state |= CMD_T_QUEUED;
-	spin_unlock_irqrestore(&qobj->cmd_queue_lock, flags);
-
-	wake_up_interruptible(&qobj->thread_wq);
-}
-
-static struct se_cmd *
-transport_get_cmd_from_queue(struct se_queue_obj *qobj)
-{
-	struct se_cmd *cmd;
-	unsigned long flags;
-
-	spin_lock_irqsave(&qobj->cmd_queue_lock, flags);
-	if (list_empty(&qobj->qobj_list)) {
-		spin_unlock_irqrestore(&qobj->cmd_queue_lock, flags);
-		return NULL;
-	}
-	cmd = list_first_entry(&qobj->qobj_list, struct se_cmd, se_queue_node);
-
-	cmd->transport_state &= ~CMD_T_QUEUED;
-	list_del_init(&cmd->se_queue_node);
-	atomic_dec(&qobj->queue_cnt);
-	spin_unlock_irqrestore(&qobj->cmd_queue_lock, flags);
-
-	return cmd;
-}
-
-static void transport_remove_cmd_from_queue(struct se_cmd *cmd)
-{
-	struct se_queue_obj *qobj = &cmd->se_dev->dev_queue_obj;
-	unsigned long flags;
-
-	spin_lock_irqsave(&qobj->cmd_queue_lock, flags);
-	if (!(cmd->transport_state & CMD_T_QUEUED)) {
-		spin_unlock_irqrestore(&qobj->cmd_queue_lock, flags);
-		return;
-	}
-	cmd->transport_state &= ~CMD_T_QUEUED;
-	atomic_dec(&qobj->queue_cnt);
-	list_del_init(&cmd->se_queue_node);
-	spin_unlock_irqrestore(&qobj->cmd_queue_lock, flags);
 }
 
 static void target_complete_failure_work(struct work_struct *work)
@@ -1132,7 +1051,6 @@ struct se_device *transport_add_device_to_core_hba(
 		return NULL;
 	}
 
-	transport_init_queue_obj(&dev->dev_queue_obj);
 	dev->dev_flags		= device_flags;
 	dev->dev_status		|= TRANSPORT_DEVICE_DEACTIVATED;
 	dev->dev_ptr		= transport_dev;
@@ -1185,10 +1103,10 @@ struct se_device *transport_add_device_to_core_hba(
 	/*
 	 * Startup the struct se_device processing thread
 	 */
-	dev->process_thread = kthread_run(transport_processing_thread, dev,
-					  "LIO_%s", dev->transport->name);
-	if (IS_ERR(dev->process_thread)) {
-		pr_err("Unable to create kthread: LIO_%s\n",
+	dev->tmr_wq = alloc_workqueue("tmr-%s", WQ_MEM_RECLAIM | WQ_UNBOUND, 1,
+				      dev->transport->name);
+	if (!dev->tmr_wq) {
+		pr_err("Unable to create tmr workqueue for %s\n",
 			dev->transport->name);
 		goto out;
 	}
@@ -1219,7 +1137,7 @@ struct se_device *transport_add_device_to_core_hba(
 
 	return dev;
 out:
-	kthread_stop(dev->process_thread);
+	destroy_workqueue(dev->tmr_wq);
 
 	spin_lock(&hba->device_lock);
 	list_del(&dev->dev_list);
@@ -1299,7 +1217,6 @@ void transport_init_se_cmd(
 	INIT_LIST_HEAD(&cmd->se_lun_node);
 	INIT_LIST_HEAD(&cmd->se_delayed_node);
 	INIT_LIST_HEAD(&cmd->se_qf_node);
-	INIT_LIST_HEAD(&cmd->se_queue_node);
 	INIT_LIST_HEAD(&cmd->se_cmd_list);
 	INIT_LIST_HEAD(&cmd->state_list);
 	init_completion(&cmd->transport_lun_fe_stop_comp);
@@ -1494,10 +1411,9 @@ int transport_handle_cdb_direct(
 		return -EINVAL;
 	}
 	/*
-	 * Set TRANSPORT_NEW_CMD state and CMD_T_ACTIVE following
-	 * transport_generic_handle_cdb*() -> transport_add_cmd_to_queue()
-	 * in existing usage to ensure that outstanding descriptors are handled
-	 * correctly during shutdown via transport_wait_for_tasks()
+	 * Set TRANSPORT_NEW_CMD state and CMD_T_ACTIVE to ensure that
+	 * outstanding descriptors are handled correctly during shutdown via
+	 * transport_wait_for_tasks()
 	 *
 	 * Also, we don't take cmd->t_state_lock here as we only expect
 	 * this to be called for initial descriptor submission.
@@ -1661,18 +1577,6 @@ int target_submit_tmr(struct se_cmd *se_cmd, struct se_session *se_sess,
 }
 EXPORT_SYMBOL(target_submit_tmr);
 
-/*	transport_generic_handle_tmr():
- *
- *
- */
-int transport_generic_handle_tmr(
-	struct se_cmd *cmd)
-{
-	transport_add_cmd_to_queue(cmd, TRANSPORT_PROCESS_TMR, false);
-	return 0;
-}
-EXPORT_SYMBOL(transport_generic_handle_tmr);
-
 /*
  * If the cmd is active, request it to be stopped and sleep until it
  * has completed.
@@ -2653,8 +2557,6 @@ static int transport_lun_wait_for_tasks(struct se_cmd *cmd, struct se_lun *lun)
 	cmd->transport_state |= CMD_T_LUN_FE_STOP;
 	spin_unlock_irqrestore(&cmd->t_state_lock, flags);
 
-	wake_up_interruptible(&cmd->se_dev->dev_queue_obj.thread_wq);
-
 	// XXX: audit task_flags checks.
 	spin_lock_irqsave(&cmd->t_state_lock, flags);
 	if ((cmd->transport_state & CMD_T_BUSY) &&
@@ -2673,7 +2575,6 @@ static int transport_lun_wait_for_tasks(struct se_cmd *cmd, struct se_lun *lun)
 		pr_debug("ConfigFS: ITT[0x%08x] - stopped cmd....\n",
 				cmd->se_tfo->get_task_tag(cmd));
 	}
-	transport_remove_cmd_from_queue(cmd);
 
 	return 0;
 }
@@ -2872,8 +2773,6 @@ bool transport_wait_for_tasks(struct se_cmd *cmd)
 
 	spin_unlock_irqrestore(&cmd->t_state_lock, flags);
 
-	wake_up_interruptible(&cmd->se_dev->dev_queue_obj.thread_wq);
-
 	wait_for_completion(&cmd->t_transport_stop_comp);
 
 	spin_lock_irqsave(&cmd->t_state_lock, flags);
@@ -3156,8 +3055,9 @@ void transport_send_task_abort(struct se_cmd *cmd)
 	cmd->se_tfo->queue_status(cmd);
 }
 
-static int transport_generic_do_tmr(struct se_cmd *cmd)
+static void target_tmr_work(struct work_struct *work)
 {
+	struct se_cmd *cmd = container_of(work, struct se_cmd, work);
 	struct se_device *dev = cmd->se_dev;
 	struct se_tmr_req *tmr = cmd->se_tmr_req;
 	int ret;
@@ -3193,54 +3093,13 @@ static int transport_generic_do_tmr(struct se_cmd *cmd)
 	cmd->se_tfo->queue_tm_rsp(cmd);
 
 	transport_cmd_check_stop_to_fabric(cmd);
-	return 0;
 }
 
-/*	transport_processing_thread():
- *
- *
- */
-static int transport_processing_thread(void *param)
+int transport_generic_handle_tmr(
+	struct se_cmd *cmd)
 {
-	int ret;
-	struct se_cmd *cmd;
-	struct se_device *dev = param;
-
-	while (!kthread_should_stop()) {
-		ret = wait_event_interruptible(dev->dev_queue_obj.thread_wq,
-				atomic_read(&dev->dev_queue_obj.queue_cnt) ||
-				kthread_should_stop());
-		if (ret < 0)
-			goto out;
-
-get_cmd:
-		cmd = transport_get_cmd_from_queue(&dev->dev_queue_obj);
-		if (!cmd)
-			continue;
-
-		switch (cmd->t_state) {
-		case TRANSPORT_NEW_CMD:
-			BUG();
-			break;
-		case TRANSPORT_PROCESS_TMR:
-			transport_generic_do_tmr(cmd);
-			break;
-		default:
-			pr_err("Unknown t_state: %d  for ITT: 0x%08x "
-				"i_state: %d on SE LUN: %u\n",
-				cmd->t_state,
-				cmd->se_tfo->get_task_tag(cmd),
-				cmd->se_tfo->get_cmd_state(cmd),
-				cmd->se_lun->unpacked_lun);
-			BUG();
-		}
-
-		goto get_cmd;
-	}
-
-out:
-	WARN_ON(!list_empty(&dev->state_list));
-	WARN_ON(!list_empty(&dev->dev_queue_obj.qobj_list));
-	dev->process_thread = NULL;
+	INIT_WORK(&cmd->work, target_tmr_work);
+	queue_work(cmd->se_dev->tmr_wq, &cmd->work);
 	return 0;
 }
+EXPORT_SYMBOL(transport_generic_handle_tmr);

include/target/target_core_base.h

@@ -147,7 +147,6 @@ enum transport_state_table {
 	TRANSPORT_WRITE_PENDING	= 3,
 	TRANSPORT_PROCESSING	= 5,
 	TRANSPORT_COMPLETE	= 6,
-	TRANSPORT_PROCESS_TMR	= 9,
 	TRANSPORT_ISTATE_PROCESSING = 11,
 	TRANSPORT_COMPLETE_QF_WP = 18,
 	TRANSPORT_COMPLETE_QF_OK = 19,
@@ -464,13 +463,6 @@ struct t10_reservation {
 	struct t10_reservation_ops pr_ops;
 };
 
-struct se_queue_obj {
-	atomic_t		queue_cnt;
-	spinlock_t		cmd_queue_lock;
-	struct list_head	qobj_list;
-	wait_queue_head_t	thread_wq;
-};
-
 struct se_tmr_req {
 	/* Task Management function to be performed */
 	u8			function;
@@ -527,7 +519,6 @@ struct se_cmd {
 	/* Only used for internal passthrough and legacy TCM fabric modules */
 	struct se_session	*se_sess;
 	struct se_tmr_req	*se_tmr_req;
-	struct list_head	se_queue_node;
 	struct list_head	se_cmd_list;
 	struct completion	cmd_wait_comp;
 	struct kref		cmd_kref;
@@ -774,7 +765,6 @@ struct se_device {
 	struct se_obj		dev_obj;
 	struct se_obj		dev_access_obj;
 	struct se_obj		dev_export_obj;
-	struct se_queue_obj	dev_queue_obj;
 	spinlock_t		delayed_cmd_lock;
 	spinlock_t		execute_task_lock;
 	spinlock_t		dev_reservation_lock;
@@ -790,8 +780,7 @@ struct se_device {
 	struct t10_pr_registration *dev_pr_res_holder;
 	struct list_head	dev_sep_list;
 	struct list_head	dev_tmr_list;
-	/* Pointer to descriptor for processing thread */
-	struct task_struct	*process_thread;
+	struct workqueue_struct *tmr_wq;
 	struct work_struct	qf_work_queue;
 	struct list_head	delayed_cmd_list;
 	struct list_head	state_list;