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

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Message-Id: <20211021002023.1128949-21-sashal@kernel.org>
Date:   Wed, 20 Oct 2021 20:20:18 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Mark Brown <broonie@...nel.org>,
        Sasha Levin <sashal@...nel.org>, linux-spi@...r.kernel.org
Subject: [PATCH AUTOSEL 5.14 21/26] spi-mux: Fix false-positive lockdep splats

From: Uwe Kleine-König <u.kleine-koenig@...gutronix.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@...gutronix.de>
Link: https://lore.kernel.org/r/20211013133710.2679703-2-u.kleine-koenig@pengutronix.de
Signed-off-by: Mark Brown <broonie@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.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