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