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