spi: Ensure the io_mutex is held until spi_finalize_current_message()

This patch introduces a completion that is completed in
spi_finalize_current_message() and waited for in
__spi_pump_transfer_message(). This way all manipulation of ctlr->cur_msg
is done with the io_mutex held and strictly ordered:
__spi_pump_transfer_message() will not return until
spi_finalize_current_message() is done using ctlr->cur_msg, and its
calling context is only touching ctlr->cur_msg after returning.
Due to this, we can safely drop the spin-locks around ctlr->cur_msg.

Signed-off-by: David Jander <david@protonic.nl>
Link: https://lore.kernel.org/r/20220621061234.3626638-11-david@protonic.nl
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -1613,11 +1613,14 @@ static int __spi_pump_transfer_message(struct spi_controller *ctlr,
 		}
 	}
 
+	reinit_completion(&ctlr->cur_msg_completion);
 	ret = ctlr->transfer_one_message(ctlr, msg);
 	if (ret) {
 		dev_err(&ctlr->dev,
 			"failed to transfer one message from queue\n");
 		return ret;
+	} else {
+		wait_for_completion(&ctlr->cur_msg_completion);
 	}
 
 	return 0;
@@ -1704,6 +1707,12 @@ static void __spi_pump_messages(struct spi_controller *ctlr, bool in_kthread)
 	spin_unlock_irqrestore(&ctlr->queue_lock, flags);
 
 	ret = __spi_pump_transfer_message(ctlr, msg, was_busy);
+
+	if (!ret)
+		kthread_queue_work(ctlr->kworker, &ctlr->pump_messages);
+	ctlr->cur_msg = NULL;
+	ctlr->fallback = false;
+
 	mutex_unlock(&ctlr->io_mutex);
 
 	/* Prod the scheduler in case transfer_one() was busy waiting */
@@ -1897,12 +1906,9 @@ void spi_finalize_current_message(struct spi_controller *ctlr)
 {
 	struct spi_transfer *xfer;
 	struct spi_message *mesg;
-	unsigned long flags;
 	int ret;
 
-	spin_lock_irqsave(&ctlr->queue_lock, flags);
 	mesg = ctlr->cur_msg;
-	spin_unlock_irqrestore(&ctlr->queue_lock, flags);
 
 	if (!ctlr->ptp_sts_supported && !ctlr->transfer_one) {
 		list_for_each_entry(xfer, &mesg->transfers, transfer_list) {
@@ -1936,20 +1942,7 @@ void spi_finalize_current_message(struct spi_controller *ctlr)
 
 	mesg->prepared = false;
 
-	if (!mesg->sync) {
+	complete(&ctlr->cur_msg_completion);
-		/*
-		 * This message was sent via the async message queue. Handle
-		 * the queue and kick the worker thread to do the
-		 * idling/shutdown or send the next message if needed.
-		 */
-		spin_lock_irqsave(&ctlr->queue_lock, flags);
-		WARN(ctlr->cur_msg != mesg,
-			"Finalizing queued message that is not the current head of queue!");
-		ctlr->cur_msg = NULL;
-		ctlr->fallback = false;
-		kthread_queue_work(ctlr->kworker, &ctlr->pump_messages);
-		spin_unlock_irqrestore(&ctlr->queue_lock, flags);
-	}
 
 	trace_spi_message_done(mesg);
 
@@ -3036,6 +3029,7 @@ int spi_register_controller(struct spi_controller *ctlr)
 	}
 	ctlr->bus_lock_flag = 0;
 	init_completion(&ctlr->xfer_completion);
+	init_completion(&ctlr->cur_msg_completion);
 	if (!ctlr->max_dma_len)
 		ctlr->max_dma_len = INT_MAX;
 
@@ -3962,6 +3956,9 @@ static void __spi_transfer_message_noqueue(struct spi_controller *ctlr, struct s
 	if (ret)
 		goto out;
 
+	ctlr->cur_msg = NULL;
+	ctlr->fallback = false;
+
 	if (!was_busy) {
 		kfree(ctlr->dummy_rx);
 		ctlr->dummy_rx = NULL;
@@ -4013,7 +4010,6 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message)
 	 * will catch those cases.
 	 */
 	if (READ_ONCE(ctlr->queue_empty)) {
-		message->sync = true;
 		message->actual_length = 0;
 		message->status = -EINPROGRESS;
 

include/linux/spi/spi.h

@@ -384,6 +384,7 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  * @queue_lock: spinlock to syncronise access to message queue
  * @queue: message queue
  * @cur_msg: the currently in-flight message
+ * @cur_msg_completion: a completion for the current in-flight message
  * @cur_msg_mapped: message has been mapped for DMA
  * @last_cs: the last chip_select that is recorded by set_cs, -1 on non chip
  *           selected
@@ -615,6 +616,7 @@ struct spi_controller {
 	spinlock_t			queue_lock;
 	struct list_head		queue;
 	struct spi_message		*cur_msg;
+	struct completion               cur_msg_completion;
 	bool				busy;
 	bool				running;
 	bool				rt;
@@ -989,7 +991,6 @@ struct spi_transfer {
  * @state: for use by whichever driver currently owns the message
  * @resources: for resource management when the spi message is processed
  * @prepared: spi_prepare_message was called for the this message
- * @sync: this message took the direct sync path skipping the async queue
  *
  * A @spi_message is used to execute an atomic sequence of data transfers,
  * each represented by a struct spi_transfer.  The sequence is "atomic"
@@ -1042,9 +1043,6 @@ struct spi_message {
 
 	/* spi_prepare_message was called for this message */
 	bool			prepared;
-
-	/* this message is skipping the async queue */
-	bool			sync;
 };
 
 static inline void spi_message_init_no_memset(struct spi_message *m)