spi: Split bus and I/O locking

The current SPI code attempts to use bus_lock_mutex for two purposes. One
is to implement spi_bus_lock() which grants exclusive access to the bus.
The other is to serialize access to the physical hardware. This duplicate
purpose causes confusion which leads to cases where access is not locked
when a caller holds the bus lock mutex. Fix this by splitting out the I/O
functionality into a new io_mutex.

This means taking both mutexes in the DMA path, replacing the existing
mutex with the new I/O one in the message pump (the mutex now always
being taken in the message pump) and taking the bus lock mutex in
spi_sync(), allowing __spi_sync() to have no mutex handling.

While we're at it hoist the mutex further up the message pump before we
power up the device so that all power up/down of the block is covered by
it and there are no races with in-line pumping of messages.
Reported-by: Rich Felker <dalias@libc.org>
Tested-by: Rich Felker <dalias@libc.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -1069,7 +1069,6 @@ EXPORT_SYMBOL_GPL(spi_finalize_current_transfer);
  * __spi_pump_messages - function which processes spi message queue
  * @master: master to process queue for
  * @in_kthread: true if we are in the context of the message pump thread
- * @bus_locked: true if the bus mutex is held when calling this function
  *
  * This function checks if there is any spi message in the queue that
  * needs processing and if so call out to the driver to initialize hardware
@@ -1079,8 +1078,7 @@ EXPORT_SYMBOL_GPL(spi_finalize_current_transfer);
  * inside spi_sync(); the queue extraction handling at the top of the
  * function should deal with this safely.
  */
-static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
-				bool bus_locked)
+static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
 {
 	unsigned long flags;
 	bool was_busy = false;
@@ -1152,6 +1150,8 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
 		master->busy = true;
 	spin_unlock_irqrestore(&master->queue_lock, flags);
 
+	mutex_lock(&master->io_mutex);
+
 	if (!was_busy && master->auto_runtime_pm) {
 		ret = pm_runtime_get_sync(master->dev.parent);
 		if (ret < 0) {
@@ -1176,9 +1176,6 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
 		}
 	}
 
-	if (!bus_locked)
-		mutex_lock(&master->bus_lock_mutex);
-
 	trace_spi_message_start(master->cur_msg);
 
 	if (master->prepare_message) {
@@ -1208,8 +1205,7 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
 	}
 
 out:
-	if (!bus_locked)
-		mutex_unlock(&master->bus_lock_mutex);
+	mutex_unlock(&master->io_mutex);
 
 	/* Prod the scheduler in case transfer_one() was busy waiting */
 	if (!ret)
@@ -1225,7 +1221,7 @@ static void spi_pump_messages(struct kthread_work *work)
 	struct spi_master *master =
 		container_of(work, struct spi_master, pump_messages);
 
-	__spi_pump_messages(master, true, master->bus_lock_flag);
+	__spi_pump_messages(master, true);
 }
 
 static int spi_init_queue(struct spi_master *master)
@@ -1887,6 +1883,7 @@ int spi_register_master(struct spi_master *master)
 	spin_lock_init(&master->queue_lock);
 	spin_lock_init(&master->bus_lock_spinlock);
 	mutex_init(&master->bus_lock_mutex);
+	mutex_init(&master->io_mutex);
 	master->bus_lock_flag = 0;
 	init_completion(&master->xfer_completion);
 	if (!master->max_dma_len)
@@ -2767,6 +2764,7 @@ int spi_flash_read(struct spi_device *spi,
 	}
 
 	mutex_lock(&master->bus_lock_mutex);
+	mutex_lock(&master->io_mutex);
 	if (master->dma_rx) {
 		rx_dev = master->dma_rx->device->dev;
 		ret = spi_map_buf(master, rx_dev, &msg->rx_sg,
@@ -2779,6 +2777,7 @@ int spi_flash_read(struct spi_device *spi,
 	if (msg->cur_msg_mapped)
 		spi_unmap_buf(master, rx_dev, &msg->rx_sg,
 			      DMA_FROM_DEVICE);
+	mutex_unlock(&master->io_mutex);
 	mutex_unlock(&master->bus_lock_mutex);
 
 	if (master->auto_runtime_pm)
@@ -2800,8 +2799,7 @@ static void spi_complete(void *arg)
 	complete(arg);
 }
 
-static int __spi_sync(struct spi_device *spi, struct spi_message *message,
-		      int bus_locked)
+static int __spi_sync(struct spi_device *spi, struct spi_message *message)
 {
 	DECLARE_COMPLETION_ONSTACK(done);
 	int status;
@@ -2819,9 +2817,6 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
 	SPI_STATISTICS_INCREMENT_FIELD(&master->statistics, spi_sync);
 	SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics, spi_sync);
 
-	if (!bus_locked)
-		mutex_lock(&master->bus_lock_mutex);
-
 	/* If we're not using the legacy transfer method then we will
 	 * try to transfer in the calling context so special case.
 	 * This code would be less tricky if we could remove the
@@ -2839,9 +2834,6 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
 		status = spi_async_locked(spi, message);
 	}
 
-	if (!bus_locked)
-		mutex_unlock(&master->bus_lock_mutex);
-
 	if (status == 0) {
 		/* Push out the messages in the calling context if we
 		 * can.
@@ -2851,7 +2843,7 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
 						       spi_sync_immediate);
 			SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics,
 						       spi_sync_immediate);
-			__spi_pump_messages(master, false, bus_locked);
+			__spi_pump_messages(master, false);
 		}
 
 		wait_for_completion(&done);
@@ -2884,7 +2876,13 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
  */
 int spi_sync(struct spi_device *spi, struct spi_message *message)
 {
-	return __spi_sync(spi, message, spi->master->bus_lock_flag);
+	int ret;
+
+	mutex_lock(&spi->master->bus_lock_mutex);
+	ret = __spi_sync(spi, message);
+	mutex_unlock(&spi->master->bus_lock_mutex);
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(spi_sync);
 
@@ -2906,7 +2904,7 @@ EXPORT_SYMBOL_GPL(spi_sync);
  */
 int spi_sync_locked(struct spi_device *spi, struct spi_message *message)
 {
-	return __spi_sync(spi, message, 1);
+	return __spi_sync(spi, message);
 }
 EXPORT_SYMBOL_GPL(spi_sync_locked);
 

include/linux/spi/spi.h

@@ -312,8 +312,9 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  * @flags: other constraints relevant to this driver
  * @max_transfer_size: function that returns the max transfer size for
  *	a &spi_device; may be %NULL, so the default %SIZE_MAX will be used.
+ * @io_mutex: mutex for physical bus access
  * @bus_lock_spinlock: spinlock for SPI bus locking
- * @bus_lock_mutex: mutex for SPI bus locking
+ * @bus_lock_mutex: mutex for exclusion of multiple callers
  * @bus_lock_flag: indicates that the SPI bus is locked for exclusive use
  * @setup: updates the device mode and clocking records used by a
  *	device's SPI controller; protocol code may call this.  This
@@ -446,6 +447,9 @@ struct spi_master {
 	 */
 	size_t (*max_transfer_size)(struct spi_device *spi);
 
+	/* I/O mutex */
+	struct mutex		io_mutex;
+
 	/* lock and mutex for SPI bus locking */
 	spinlock_t		bus_lock_spinlock;
 	struct mutex		bus_lock_mutex;