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@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
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);
--
Christian Eggers
Embedded software developer
Arnold & Richter Cine Technik GmbH & Co. Betriebs KG
Sitz: Muenchen - Registergericht: Amtsgericht Muenchen - Handelsregisternummer: HRA 57918
Persoenlich haftender Gesellschafter: Arnold & Richter Cine Technik GmbH
Sitz: Muenchen - Registergericht: Amtsgericht Muenchen - Handelsregisternummer: HRB 54477
Geschaeftsfuehrer: Dr. Michael Neuhaeuser; Stephan Schenk; Walter Trauninger; Markus Zeiler
