[PATCH AUTOSEL 5.14 20/26] spi: Fix deadlock when adding SPI controllers on SPI buses

[PATCH AUTOSEL 5.14 20/26] spi: Fix deadlock when adding SPI controllers on SPI buses

[Sasha Levin]

From: Mark Brown <broonie@kernel.org>

[ Upstream commit 6098475d4cb48d821bdf453c61118c56e26294f0 ]

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: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/spi/spi.c       | 17 ++++++-----------
 include/linux/spi/spi.h |  3 +++
 2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index f95f7666cb5b..2c342bded058 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -480,12 +480,6 @@ 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
@@ -638,9 +632,9 @@ 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);
@@ -660,7 +654,7 @@ 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);
 }
 
@@ -2832,6 +2826,7 @@ 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)
@@ -2968,7 +2963,7 @@ 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);
 
@@ -2999,7 +2994,7 @@ 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);
 
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 97b8d12b5f2b..5d80c6fd2a22 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -527,6 +527,9 @@ 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;
-- 
2.33.0

[PATCH AUTOSEL 5.14 21/26] spi-mux: Fix false-positive lockdep splats

[Sasha Levin]

From: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

[ Upstream commit 16a8e2fbb2d49111004efc1c7342e083eafabeb0 ]

io_mutex is taken by spi_setup() and spi-mux's .setup() callback calls
spi_setup() which results in a nested lock of io_mutex.

add_lock is taken by spi_add_device(). The device_add() call in there
can result in calling spi-mux's .probe() callback which registers its
own spi controller which in turn results in spi_add_device() being
called again.

To fix this initialize the controller's locks already in
spi_alloc_controller() to give spi_mux_probe() a chance to set the
lockdep subclass.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211013133710.2679703-2-u.kleine-koenig@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/spi/spi-mux.c |  7 +++++++
 drivers/spi/spi.c     | 12 ++++++------
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/spi/spi-mux.c b/drivers/spi/spi-mux.c
index 9708b7827ff7..f5d32ec4634e 100644
--- a/drivers/spi/spi-mux.c
+++ b/drivers/spi/spi-mux.c
@@ -137,6 +137,13 @@ static int spi_mux_probe(struct spi_device *spi)
 	priv = spi_controller_get_devdata(ctlr);
 	priv->spi = spi;
 
+	/*
+	 * Increase lockdep class as these lock are taken while the parent bus
+	 * already holds their instance's lock.
+	 */
+	lockdep_set_subclass(&ctlr->io_mutex, 1);
+	lockdep_set_subclass(&ctlr->add_lock, 1);
+
 	priv->mux = devm_mux_control_get(&spi->dev, NULL);
 	if (IS_ERR(priv->mux)) {
 		ret = dev_err_probe(&spi->dev, PTR_ERR(priv->mux),
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 2c342bded058..3093e0041158 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2549,6 +2549,12 @@ struct spi_controller *__spi_alloc_controller(struct device *dev,
 		return NULL;
 
 	device_initialize(&ctlr->dev);
+	INIT_LIST_HEAD(&ctlr->queue);
+	spin_lock_init(&ctlr->queue_lock);
+	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_num = -1;
 	ctlr->num_chipselect = 1;
 	ctlr->slave = slave;
@@ -2821,12 +2827,6 @@ int spi_register_controller(struct spi_controller *ctlr)
 			return id;
 		ctlr->bus_num = id;
 	}
-	INIT_LIST_HEAD(&ctlr->queue);
-	spin_lock_init(&ctlr->queue_lock);
-	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)
-- 
2.33.0