Unverified Commit 6098475d authored by Mark Brown's avatar Mark Brown
Browse files

spi: Fix deadlock when adding SPI controllers on SPI buses 



Currently we have a global spi_add_lock which we take when adding new
devices so that we can check that we're not trying to reuse a chip
select that's already controlled.  This means that if the SPI device is
itself a SPI controller and triggers the instantiation of further SPI
devices we trigger a deadlock as we try to register and instantiate
those devices while in the process of doing so for the parent controller
and hence already holding the global spi_add_lock.  Since we only care
about concurrency within a single SPI bus move the lock to be per
controller, avoiding the deadlock.

This can be easily triggered in the case of spi-mux.

Reported-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 75b3cb97

drivers/spi/spi.c

+6 −11
Original line number Diff line number Diff line
@@ -478,12 +478,6 @@ static LIST_HEAD(spi_controller_list); 
 */

static DEFINE_MUTEX(board_lock);



/*

 * Prevents addition of devices with same chip select and

 * addition of devices below an unregistering controller.

 */

static DEFINE_MUTEX(spi_add_lock);



/**

 * spi_alloc_device - Allocate a new SPI device

 * @ctlr: Controller to which device is connected
@@ -636,9 +630,9 @@ int spi_add_device(struct spi_device *spi) 
	 * chipselect **BEFORE** we call setup(), else we'll trash

	 * its configuration.  Lock against concurrent add() calls.

	 */

	mutex_lock(&spi_add_lock);

	mutex_lock(&ctlr->add_lock);

	status = __spi_add_device(spi);

	mutex_unlock(&spi_add_lock);

	mutex_unlock(&ctlr->add_lock);

	return status;

}

EXPORT_SYMBOL_GPL(spi_add_device);
@@ -658,7 +652,7 @@ static int spi_add_device_locked(struct spi_device *spi) 
	/* Set the bus ID string */

	spi_dev_set_name(spi);



	WARN_ON(!mutex_is_locked(&spi_add_lock));

	WARN_ON(!mutex_is_locked(&ctlr->add_lock));

	return __spi_add_device(spi);

}
@@ -2830,6 +2824,7 @@ int spi_register_controller(struct spi_controller *ctlr) 
	spin_lock_init(&ctlr->bus_lock_spinlock);

	mutex_init(&ctlr->bus_lock_mutex);

	mutex_init(&ctlr->io_mutex);

	mutex_init(&ctlr->add_lock);

	ctlr->bus_lock_flag = 0;

	init_completion(&ctlr->xfer_completion);

	if (!ctlr->max_dma_len)
@@ -2966,7 +2961,7 @@ void spi_unregister_controller(struct spi_controller *ctlr) 


	/* Prevent addition of new devices, unregister existing ones */

	if (IS_ENABLED(CONFIG_SPI_DYNAMIC))

		mutex_lock(&spi_add_lock);

		mutex_lock(&ctlr->add_lock);



	device_for_each_child(&ctlr->dev, NULL, __unregister);
@@ -2997,7 +2992,7 @@ void spi_unregister_controller(struct spi_controller *ctlr) 
	mutex_unlock(&board_lock);



	if (IS_ENABLED(CONFIG_SPI_DYNAMIC))

		mutex_unlock(&spi_add_lock);

		mutex_unlock(&ctlr->add_lock);

}

EXPORT_SYMBOL_GPL(spi_unregister_controller);

include/linux/spi/spi.h

+3 −0
Original line number Diff line number Diff line
@@ -531,6 +531,9 @@ struct spi_controller { 
	/* I/O mutex */

	struct mutex		io_mutex;



	/* Used to avoid adding the same CS twice */

	struct mutex		add_lock;



	/* lock and mutex for SPI bus locking */

	spinlock_t		bus_lock_spinlock;

	struct mutex		bus_lock_mutex;