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spi: Split bus and I/O locking
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The current SPI code attempts to use bus_lock_mutex for two purposes. One
is to implement spi_bus_lock() which grants exclusive access to the bus.
The other is to serialize access to the physical hardware. This duplicate
purpose causes confusion which leads to cases where access is not locked
when a caller holds the bus lock mutex. Fix this by splitting out the I/O
functionality into a new io_mutex.

This means taking both mutexes in the DMA path, replacing the existing
mutex with the new I/O one in the message pump (the mutex now always
being taken in the message pump) and taking the bus lock mutex in
spi_sync(), allowing __spi_sync() to have no mutex handling.

While we're at it hoist the mutex further up the message pump before we
power up the device so that all power up/down of the block is covered by
it and there are no races with in-line pumping of messages.

Reported-by: Rich Felker <[email protected]>
Tested-by: Rich Felker <[email protected]>
Signed-off-by: Mark Brown <[email protected]>
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@broonie
broonie committed Jul 25, 2016
1 parent f4502dd commit ef4d96e
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Showing 2 changed files with 23 additions and 21 deletions.
38 changes: 18 additions & 20 deletions drivers/spi/spi.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1069,7 +1069,6 @@ EXPORT_SYMBOL_GPL(spi_finalize_current_transfer);
* __spi_pump_messages - function which processes spi message queue
* @master: master to process queue for
* @in_kthread: true if we are in the context of the message pump thread
* @bus_locked: true if the bus mutex is held when calling this function
*
* This function checks if there is any spi message in the queue that
* needs processing and if so call out to the driver to initialize hardware
Expand All @@ -1079,8 +1078,7 @@ EXPORT_SYMBOL_GPL(spi_finalize_current_transfer);
* inside spi_sync(); the queue extraction handling at the top of the
* function should deal with this safely.
*/
static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
bool bus_locked)
static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
{
unsigned long flags;
bool was_busy = false;
Expand Down Expand Up @@ -1152,6 +1150,8 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
master->busy = true;
spin_unlock_irqrestore(&master->queue_lock, flags);

mutex_lock(&master->io_mutex);

if (!was_busy && master->auto_runtime_pm) {
ret = pm_runtime_get_sync(master->dev.parent);
if (ret < 0) {
Expand All @@ -1176,9 +1176,6 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
}
}

if (!bus_locked)
mutex_lock(&master->bus_lock_mutex);

trace_spi_message_start(master->cur_msg);

if (master->prepare_message) {
Expand Down Expand Up @@ -1208,8 +1205,7 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
}

out:
if (!bus_locked)
mutex_unlock(&master->bus_lock_mutex);
mutex_unlock(&master->io_mutex);

/* Prod the scheduler in case transfer_one() was busy waiting */
if (!ret)
Expand All @@ -1225,7 +1221,7 @@ static void spi_pump_messages(struct kthread_work *work)
struct spi_master *master =
container_of(work, struct spi_master, pump_messages);

__spi_pump_messages(master, true, master->bus_lock_flag);
__spi_pump_messages(master, true);
}

static int spi_init_queue(struct spi_master *master)
Expand Down Expand Up @@ -1887,6 +1883,7 @@ int spi_register_master(struct spi_master *master)
spin_lock_init(&master->queue_lock);
spin_lock_init(&master->bus_lock_spinlock);
mutex_init(&master->bus_lock_mutex);
mutex_init(&master->io_mutex);
master->bus_lock_flag = 0;
init_completion(&master->xfer_completion);
if (!master->max_dma_len)
Expand Down Expand Up @@ -2767,6 +2764,7 @@ int spi_flash_read(struct spi_device *spi,
}

mutex_lock(&master->bus_lock_mutex);
mutex_lock(&master->io_mutex);
if (master->dma_rx) {
rx_dev = master->dma_rx->device->dev;
ret = spi_map_buf(master, rx_dev, &msg->rx_sg,
Expand All @@ -2779,6 +2777,7 @@ int spi_flash_read(struct spi_device *spi,
if (msg->cur_msg_mapped)
spi_unmap_buf(master, rx_dev, &msg->rx_sg,
DMA_FROM_DEVICE);
mutex_unlock(&master->io_mutex);
mutex_unlock(&master->bus_lock_mutex);

if (master->auto_runtime_pm)
Expand All @@ -2800,8 +2799,7 @@ static void spi_complete(void *arg)
complete(arg);
}

static int __spi_sync(struct spi_device *spi, struct spi_message *message,
int bus_locked)
static int __spi_sync(struct spi_device *spi, struct spi_message *message)
{
DECLARE_COMPLETION_ONSTACK(done);
int status;
Expand All @@ -2819,9 +2817,6 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
SPI_STATISTICS_INCREMENT_FIELD(&master->statistics, spi_sync);
SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics, spi_sync);

if (!bus_locked)
mutex_lock(&master->bus_lock_mutex);

/* If we're not using the legacy transfer method then we will
* try to transfer in the calling context so special case.
* This code would be less tricky if we could remove the
Expand All @@ -2839,9 +2834,6 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
status = spi_async_locked(spi, message);
}

if (!bus_locked)
mutex_unlock(&master->bus_lock_mutex);

if (status == 0) {
/* Push out the messages in the calling context if we
* can.
Expand All @@ -2851,7 +2843,7 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
spi_sync_immediate);
SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics,
spi_sync_immediate);
__spi_pump_messages(master, false, bus_locked);
__spi_pump_messages(master, false);
}

wait_for_completion(&done);
Expand Down Expand Up @@ -2884,7 +2876,13 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
*/
int spi_sync(struct spi_device *spi, struct spi_message *message)
{
return __spi_sync(spi, message, spi->master->bus_lock_flag);
int ret;

mutex_lock(&spi->master->bus_lock_mutex);
ret = __spi_sync(spi, message);
mutex_unlock(&spi->master->bus_lock_mutex);

return ret;
}
EXPORT_SYMBOL_GPL(spi_sync);

Expand All @@ -2906,7 +2904,7 @@ EXPORT_SYMBOL_GPL(spi_sync);
*/
int spi_sync_locked(struct spi_device *spi, struct spi_message *message)
{
return __spi_sync(spi, message, 1);
return __spi_sync(spi, message);
}
EXPORT_SYMBOL_GPL(spi_sync_locked);

Expand Down
6 changes: 5 additions & 1 deletion include/linux/spi/spi.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -312,8 +312,9 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
* @flags: other constraints relevant to this driver
* @max_transfer_size: function that returns the max transfer size for
* a &spi_device; may be %NULL, so the default %SIZE_MAX will be used.
* @io_mutex: mutex for physical bus access
* @bus_lock_spinlock: spinlock for SPI bus locking
* @bus_lock_mutex: mutex for SPI bus locking
* @bus_lock_mutex: mutex for exclusion of multiple callers
* @bus_lock_flag: indicates that the SPI bus is locked for exclusive use
* @setup: updates the device mode and clocking records used by a
* device's SPI controller; protocol code may call this. This
Expand Down Expand Up @@ -446,6 +447,9 @@ struct spi_master {
*/
size_t (*max_transfer_size)(struct spi_device *spi);

/* I/O mutex */
struct mutex io_mutex;

/* lock and mutex for SPI bus locking */
spinlock_t bus_lock_spinlock;
struct mutex bus_lock_mutex;
Expand Down

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