On Wed, Oct 13, 2021 at 01:26:28PM +0100, Mark Brown wrote:
> 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@xxxxxxxxxxxxxx>
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
> ---
> drivers/spi/spi.c | 21 ++++++++++-----------
> include/linux/spi/spi.h | 3 +++
> 2 files changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 401f62f6f5b5..71d061132ada 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -518,12 +518,6 @@ 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
> @@ -676,9 +670,13 @@ static int spi_add_device(struct spi_device *spi)
> /* Set the bus ID string */
> spi_dev_set_name(spi);
>
> - mutex_lock(&spi_add_lock);
> + /* We need to make sure there's no other device with this
> + * chipselect **BEFORE** we call setup(), else we'll trash
> + * its configuration. Lock against concurrent add() calls.
> + */
This comment is already there, it seems you duplicated it with your
patch? Maybe a merge issue with
6bfb15f34dd8c8a073e03a31c485ef5774b127df?
> + mutex_lock(&ctlr->add_lock);
> status = __spi_add_device(spi);
> - mutex_unlock(&spi_add_lock);
> + mutex_unlock(&ctlr->add_lock);
> return status;
> }
>
> @@ -697,7 +695,7 @@ 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);
> }
>
> @@ -2950,6 +2948,7 @@ 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)
> @@ -3086,7 +3085,7 @@ 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);
>
> @@ -3117,7 +3116,7 @@ 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 29e21d49aafc..eb7ac8a1e03c 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;
> +
Kernel-doc is missing for that one.
(In the local patch I have for testing here, I wrote:
* @add_lock: mutex to avoid adding two devices on the same CS
.)
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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