Triggers may raise transactions on slow busses like I2C. Using the original RT priority of a threaded IRQ may prevent other important IRQ handlers from being run.
In my particular case (on a RT kernel), the RT priority of the sysfstrig threaded IRQ handler caused (temporarily) raising the prio of a user space process which was holding the I2C bus mutex.
Although this process did nothing more than blocking on i2c-dev ioctl(), no other threaded IRQ handlers (like DMA) were switched in during this time.
Signed-off-by: Christian Eggers ceggers@arri.de Cc: stable@vger.kernel.org --- drivers/iio/industrialio-trigger.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/drivers/iio/industrialio-trigger.c b/drivers/iio/industrialio-trigger.c index 6f16357fd732..b74180293da2 100644 --- a/drivers/iio/industrialio-trigger.c +++ b/drivers/iio/industrialio-trigger.c @@ -9,8 +9,12 @@ #include <linux/err.h> #include <linux/device.h> #include <linux/interrupt.h> +#include <linux/irq.h> +#include <linux/irqdesc.h> #include <linux/list.h> +#include <linux/sched.h> #include <linux/slab.h> +#include <uapi/linux/sched/types.h>
#include <linux/iio/iio.h> #include <linux/iio/trigger.h> @@ -245,6 +249,8 @@ int iio_trigger_attach_poll_func(struct iio_trigger *trig, int ret = 0; bool notinuse = bitmap_empty(trig->pool, CONFIG_IIO_CONSUMERS_PER_TRIGGER); + struct sched_param sched_param = { .sched_priority = 0 }; + struct irq_desc *irq_desc;
/* Prevent the module from being removed whilst attached to a trigger */ __module_get(pf->indio_dev->driver_module); @@ -264,6 +270,12 @@ int iio_trigger_attach_poll_func(struct iio_trigger *trig, if (ret < 0) goto out_put_irq;
+ /* Triggers may raise transactions on slow busses like I2C. Using the original RT priority + * of a threaded IRQ may prevent other threaded IRQ handlers from being run. + */ + irq_desc = irq_to_desc(pf->irq); + sched_setscheduler_nocheck(irq_desc->action->thread, SCHED_NORMAL, &sched_param); + /* Enable trigger in driver */ if (trig->ops && trig->ops->set_trigger_state && notinuse) { ret = trig->ops->set_trigger_state(trig, true);