[PATCH 38/40] scsi: libiscsi: replace list_head with llist_head

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This replaces the cmdqueue and requeue list_heads with llist_heads. We
can do not need the frwd_lock in the queuecommand and recv paths for
this. This patch does not yet cleanup the frwd_lock because we still
need it for the cmdsn handling. When that is fixed up the next patches
then the frwd_lock will be completely removed for the software case.

Signed-off-by: Mike Christie <michael.christie@xxxxxxxxxx>
---
 drivers/scsi/libiscsi.c | 248 +++++++++++++++++++++++++++++-----------
 include/scsi/libiscsi.h |  23 ++--
 2 files changed, 198 insertions(+), 73 deletions(-)

diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
index 1c134f721a56..1b4b6ee246cf 100644
--- a/drivers/scsi/libiscsi.c
+++ b/drivers/scsi/libiscsi.c
@@ -730,7 +730,6 @@ iscsi_alloc_mgmt_task(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
 	refcount_set(&task->refcount, 1);
 	task->conn = conn;
 	task->sc = NULL;
-	INIT_LIST_HEAD(&task->running);
 	task->state = ISCSI_TASK_PENDING;
 
 	if (data_size) {
@@ -782,7 +781,7 @@ static int iscsi_send_mgmt_task(struct iscsi_task *task)
 		if (rc)
 			return rc;
 	} else {
-		list_add_tail(&task->running, &conn->mgmtqueue);
+		list_add_tail(&task->running, &conn->mgmt_exec_list);
 		iscsi_conn_queue_work(conn);
 	}
 
@@ -1564,7 +1563,6 @@ 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->session->frwd_lock);
 	spin_lock(&task->lock);
 	if (task->state == ISCSI_TASK_REQUEUED) {
 		/*
@@ -1574,129 +1572,238 @@ void iscsi_requeue_task(struct iscsi_task *task)
 		iscsi_put_task(task);
 	} else {
 		task->state = ISCSI_TASK_REQUEUED;
-		list_add_tail(&task->running, &conn->requeue);
+		llist_add(&task->queue, &conn->requeue);
 	}
 	spin_unlock(&task->lock);
 
 	iscsi_conn_queue_work(conn);
-	spin_unlock_bh(&conn->session->frwd_lock);
 }
 EXPORT_SYMBOL_GPL(iscsi_requeue_task);
 
-/**
- * iscsi_data_xmit - xmit any command into the scheduled connection
- * @conn: iscsi connection
- *
- * Notes:
- *	The function can return -EAGAIN in which case the caller must
- *	re-schedule it again later or recover. '0' return code means
- *	successful xmit.
- **/
-static int iscsi_data_xmit(struct iscsi_conn *conn)
+static bool iscsi_move_tasks(struct llist_head *submit_queue,
+			     struct list_head *exec_queue)
 {
-	struct iscsi_task *task;
-	int rc = 0, cnt;
-
-	spin_lock_bh(&conn->session->frwd_lock);
-	if (test_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx)) {
-		ISCSI_DBG_SESSION(conn->session, "Tx suspended!\n");
-		spin_unlock_bh(&conn->session->frwd_lock);
-		return -ENODATA;
-	}
-
-	if (conn->task) {
-		rc = iscsi_xmit_task(conn, conn->task, false);
-	        if (rc)
-		        goto done;
-	}
+	struct iscsi_task *task, *next_task;
+	struct list_head *list_end;
+	struct llist_node *node;
 
 	/*
-	 * process mgmt pdus like nops before commands since we should
-	 * only have one nop-out as a ping from us and targets should not
-	 * overflow us with nop-ins
+	 * The llist_head is in the reverse order cmds were submitted in. We
+	 * are going to reverse it here. If the exec_queue is empty we want
+	 * to add cmds at starting at head. If the exec_queue has cmds from a
+	 * previous call then we need to start adding this batch at the end of
+	 * the last batch.
 	 */
-check_mgmt:
-	while (!list_empty(&conn->mgmtqueue)) {
-		task = list_entry(conn->mgmtqueue.next, struct iscsi_task,
+	list_end = exec_queue->prev;
+
+	node = llist_del_all(submit_queue);
+	llist_for_each_entry_safe(task, next_task, node, queue)
+		list_add(&task->running, list_end);
+
+	return !list_empty(exec_queue);
+}
+
+static void iscsi_move_all_tasks(struct iscsi_conn *conn)
+{
+	iscsi_move_tasks(&conn->requeue, &conn->requeue_exec_list);
+	iscsi_move_tasks(&conn->cmdqueue, &conn->cmd_exec_list);
+}
+
+static int iscsi_exec_mgmt_tasks(struct iscsi_conn *conn)
+{
+	struct iscsi_task *task;
+	int rc;
+
+	while (!list_empty(&conn->mgmt_exec_list)) {
+		task = list_entry(conn->mgmt_exec_list.next, struct iscsi_task,
 				  running);
 		list_del_init(&task->running);
+
 		if (iscsi_prep_mgmt_task(conn, task)) {
 			iscsi_put_task(task);
 			continue;
 		}
+
 		rc = iscsi_xmit_task(conn, task, false);
 		if (rc)
-			goto done;
+			return rc;
 	}
 
-check_requeue:
-	while (!list_empty(&conn->requeue)) {
+	return 0;
+}
+
+static int iscsi_exec_requeued_tasks(struct iscsi_conn *conn, unsigned int *cnt)
+{
+	struct iscsi_task *task;
+	int rc = 0;
+
+	while (!list_empty(&conn->requeue_exec_list)) {
 		/*
 		 * we always do fastlogout - conn stop code will clean up.
 		 */
 		if (READ_ONCE(conn->session->state) == ISCSI_STATE_LOGGING_OUT)
 			break;
 
-		task = list_entry(conn->requeue.next, struct iscsi_task,
-				  running);
+		task = list_entry(conn->requeue_exec_list.next,
+				  struct iscsi_task, running);
 
 		if (iscsi_check_tmf_restrictions(task, ISCSI_OP_SCSI_DATA_OUT))
 			break;
 
 		spin_lock_bh(&task->lock);
-		task->state = ISCSI_TASK_RUNNING;
+		/*
+		 * We might have raced and handld multiple R2Ts in one run.
+		 */
 		list_del_init(&task->running);
+		if (task->state == ISCSI_TASK_COMPLETED) {
+			spin_unlock_bh(&task->lock);
+			iscsi_put_task(task);
+			continue;
+		}
+
+		task->state = ISCSI_TASK_RUNNING;
 		spin_unlock_bh(&task->lock);
 
 		rc = iscsi_xmit_task(conn, task, true);
 		if (rc)
-			goto done;
-		if (!list_empty(&conn->mgmtqueue))
-			goto check_mgmt;
+			break;
+		(*cnt)++;
+
+		rc = iscsi_exec_mgmt_tasks(conn);
+		if (rc)
+			break;
 	}
 
-	/* process pending command queue */
-	cnt = 0;
-	while (!list_empty(&conn->cmdqueue)) {
-		task = list_entry(conn->cmdqueue.next, struct iscsi_task,
+	ISCSI_DBG_CONN(conn, "executed %u requeued cmds.\n", *cnt);
+	return rc;
+}
+
+static int iscsi_exec_tasks(struct iscsi_conn *conn,
+			    struct llist_head *submit_queue,
+			    struct list_head *exec_queue,
+			    int (*exec_fn)(struct iscsi_conn *conn,
+					   unsigned int *cnt))
+{
+	unsigned int cnt = 0;
+	int rc = 0;
+
+	while (iscsi_move_tasks(submit_queue, exec_queue)) {
+		rc = exec_fn(conn, &cnt);
+		if (rc)
+			break;
+
+	}
+
+	ISCSI_DBG_CONN(conn, "executed %u total %s cmds.\n", cnt,
+		       exec_fn == iscsi_exec_requeued_tasks ?
+		       "requeued" : "new");
+	return 0;
+}
+
+static int iscsi_exec_cmd_tasks(struct iscsi_conn *conn, unsigned int *cnt)
+{
+	struct iscsi_task *task;
+	int rc = 0;
+
+	while (!list_empty(&conn->cmd_exec_list)) {
+		task = list_entry(conn->cmd_exec_list.next, struct iscsi_task,
 				  running);
 		list_del_init(&task->running);
+
 		if (READ_ONCE(conn->session->state) == ISCSI_STATE_LOGGING_OUT) {
 			fail_scsi_task(task, DID_IMM_RETRY);
 			continue;
 		}
+
 		rc = iscsi_prep_scsi_cmd_pdu(task);
 		if (rc) {
 			if (rc == -ENOMEM || rc == -EACCES)
 				fail_scsi_task(task, DID_IMM_RETRY);
 			else
 				fail_scsi_task(task, DID_ABORT);
+			rc = 0;
 			continue;
 		}
+
 		rc = iscsi_xmit_task(conn, task, false);
 		if (rc)
-			goto done;
+			break;
+		(*cnt)++;
+
 		/*
-		 * we could continuously get new task requests so
-		 * we need to check the mgmt queue for nops that need to
-		 * be sent to aviod starvation
+		 * Make sure we handle target pings quickly so it doesn't
+		 * timeout and drop the conn on us.
 		 */
-		if (!list_empty(&conn->mgmtqueue))
-			goto check_mgmt;
+		rc = iscsi_exec_mgmt_tasks(conn);
+		if (rc)
+			break;
 		/*
 		 * Avoid starving the requeue list if new cmds keep coming in.
 		 * Incase the app tried to batch cmds to us, we allow up to
 		 * queueing limit.
 		 */
-		cnt++;
-		if (cnt == conn->session->host->cmd_per_lun) {
-			cnt = 0;
+		if (*cnt == conn->session->host->cmd_per_lun) {
+			*cnt = 0;
+
+			ISCSI_DBG_CONN(conn, "hit dequeue limit.\n");
 
-			if (!list_empty(&conn->requeue))
-				goto check_requeue;
+			rc = iscsi_exec_tasks(conn, &conn->requeue,
+					      &conn->requeue_exec_list,
+					      iscsi_exec_requeued_tasks);
+			if (rc)
+				break;
 		}
 	}
 
+	ISCSI_DBG_CONN(conn, "executed %u cmds.\n", *cnt);
+	return rc;
+}
+
+/**
+ * iscsi_data_xmit - xmit any command into the scheduled connection
+ * @conn: iscsi connection
+ *
+ * Notes:
+ *	The function can return -EAGAIN in which case the caller must
+ *	re-schedule it again later or recover. '0' return code means
+ *	successful xmit.
+ **/
+static int iscsi_data_xmit(struct iscsi_conn *conn)
+{
+	int rc = 0;
+
+	spin_lock_bh(&conn->session->frwd_lock);
+	if (test_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx)) {
+		ISCSI_DBG_SESSION(conn->session, "Tx suspended!\n");
+		spin_unlock_bh(&conn->session->frwd_lock);
+		return -ENODATA;
+	}
+
+	if (conn->task) {
+		rc = iscsi_xmit_task(conn, conn->task, false);
+		if (rc)
+			goto done;
+	}
+
+	/*
+	 * process mgmt pdus like nops before commands since we should
+	 * only have one nop-out as a ping from us and targets should not
+	 * overflow us with nop-ins
+	 */
+	rc = iscsi_exec_mgmt_tasks(conn);
+	if (rc)
+		goto done;
+
+	rc = iscsi_exec_tasks(conn, &conn->requeue, &conn->requeue_exec_list,
+			      iscsi_exec_requeued_tasks);
+	if (rc)
+		goto done;
+
+	rc = iscsi_exec_tasks(conn, &conn->cmdqueue, &conn->cmd_exec_list,
+			      iscsi_exec_cmd_tasks);
+	if (rc)
+		goto done;
+
 	spin_unlock_bh(&conn->session->frwd_lock);
 	return -ENODATA;
 
@@ -1732,7 +1839,6 @@ static struct iscsi_task *iscsi_init_scsi_task(struct iscsi_conn *conn,
 	task->last_timeout = jiffies;
 	task->last_xfer = jiffies;
 	task->protected = false;
-	INIT_LIST_HEAD(&task->running);
 
 	spin_lock_bh(&task->lock);
 	task->state = ISCSI_TASK_PENDING;
@@ -1862,7 +1968,7 @@ int iscsi_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *sc)
 		}
 	} else {
 		task = iscsi_init_scsi_task(conn, sc);
-		list_add_tail(&task->running, &conn->cmdqueue);
+		llist_add(&task->queue, &conn->cmdqueue);
 		iscsi_conn_queue_work(conn);
 	}
 
@@ -2028,6 +2134,8 @@ static void fail_scsi_tasks(struct iscsi_conn *conn, u64 lun, int error)
 		.data = &error,
 	};
 
+	/* Make sure we don't leave cmds in the queues */
+	iscsi_move_all_tasks(conn);
 	iscsi_conn_for_each_sc(conn, &iter_data);
 }
 
@@ -2381,7 +2489,12 @@ int iscsi_eh_abort(struct scsi_cmnd *sc)
 	ISCSI_DBG_EH(session, "aborting [sc %p itt 0x%x]\n", sc, task->itt);
 
 	spin_lock_bh(&task->lock);
-	if (task->state == ISCSI_TASK_PENDING) {
+	/*
+	 * If we haven't sent the cmd, but it's still on the cmdqueue we
+	 * don't have an easy way to dequeue that single cmd here.
+	 * iscsi_check_tmf_restrictions will end up handling it.
+	 */
+	if (task->state == ISCSI_TASK_PENDING && !list_empty(&task->running)) {
 		spin_unlock_bh(&task->lock);
 
 		fail_scsi_task(task, DID_ABORT);
@@ -3174,9 +3287,12 @@ iscsi_conn_setup(struct iscsi_cls_session *cls_session, int dd_size,
 
 	timer_setup(&conn->transport_timer, iscsi_check_transport_timeouts, 0);
 
-	INIT_LIST_HEAD(&conn->mgmtqueue);
-	INIT_LIST_HEAD(&conn->cmdqueue);
-	INIT_LIST_HEAD(&conn->requeue);
+	init_llist_head(&conn->cmdqueue);
+	init_llist_head(&conn->requeue);
+	INIT_LIST_HEAD(&conn->cmd_exec_list);
+	INIT_LIST_HEAD(&conn->mgmt_exec_list);
+	INIT_LIST_HEAD(&conn->requeue_exec_list);
+
 	INIT_WORK(&conn->xmitwork, iscsi_xmitworker);
 
 	/* allocate login_task used for the login/text sequences */
diff --git a/include/scsi/libiscsi.h b/include/scsi/libiscsi.h
index 358701227f7f..21579d3dc1f6 100644
--- a/include/scsi/libiscsi.h
+++ b/include/scsi/libiscsi.h
@@ -150,7 +150,8 @@ struct iscsi_task {
 	spinlock_t		lock;
 	int			state;
 	refcount_t		refcount;
-	struct list_head	running;	/* running cmd list */
+	struct llist_node	queue;
+	struct list_head	running;
 	void			*dd_data;	/* driver/transport data */
 };
 
@@ -212,10 +213,18 @@ struct iscsi_conn {
 	struct iscsi_task	*task;		/* xmit task in progress */
 
 	/* xmit */
-	/* 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 */
+	struct llist_head	cmdqueue;	/* data-path cmd queue */
+	struct llist_head	requeue;	/* tasks needing another run */
+
+	/* The frwd_lock is used to access these lists in the xmit and eh path */
+	struct list_head	cmd_exec_list;
+	struct list_head	requeue_exec_list;
+	/*
+	 * The frwd_lock is used to access this list in the xmit, eh and
+	 * submission paths.
+	 */
+	struct list_head	mgmt_exec_list;
+
 	struct work_struct	xmitwork;	/* per-conn. xmit workqueue */
 	unsigned long		suspend_tx;	/* suspend Tx */
 	unsigned long		suspend_rx;	/* suspend Rx */
@@ -352,8 +361,8 @@ struct iscsi_session {
 	struct iscsi_conn	*leadconn;	/* leading connection */
 	spinlock_t		frwd_lock;	/* protects queued_cmdsn,  *
 						 * cmdsn, suspend_bit,     *
-						 * _stage, tmf_state and   *
-						 * queues                  */
+						 * _stage, exec lists, and
+						 * tmf_state    */
 	/*
 	 * frwd_lock must be held when transitioning states, but not needed
 	 * if just checking the state in the scsi-ml or iscsi callouts.
-- 
2.25.1




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