iio:trigger: Fix use_count race condition
When using more than one trigger consumer it can happen that multiple threads perform a read-modify-update cycle on 'use_count' concurrently. This can cause updates to be lost and use_count can get stuck at non-zero value, in which case the IIO core assumes that at least one thread is still running and will wait for it to finish before running any trigger handlers again. This effectively renders the trigger disabled and a reboot is necessary before it can be used again. To fix this make use_count an atomic variable. Also set it to the number of consumers before starting the first consumer, otherwise it might happen that use_count drops to 0 even though not all consumers have been run yet. Signed-off-by: Lars-Peter Clausen <lars@metafoo.de> Tested-by: Denis Ciocca <denis.ciocca@st.com> Signed-off-by: Jonathan Cameron <jic23@kernel.org>
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@ -127,12 +127,17 @@ static struct iio_trigger *iio_trigger_find_by_name(const char *name,
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void iio_trigger_poll(struct iio_trigger *trig, s64 time)
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{
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int i;
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if (!trig->use_count)
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for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++)
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if (trig->subirqs[i].enabled) {
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trig->use_count++;
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if (!atomic_read(&trig->use_count)) {
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atomic_set(&trig->use_count, CONFIG_IIO_CONSUMERS_PER_TRIGGER);
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for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++) {
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if (trig->subirqs[i].enabled)
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generic_handle_irq(trig->subirq_base + i);
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}
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else
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iio_trigger_notify_done(trig);
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}
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}
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}
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EXPORT_SYMBOL(iio_trigger_poll);
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@ -146,19 +151,24 @@ EXPORT_SYMBOL(iio_trigger_generic_data_rdy_poll);
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void iio_trigger_poll_chained(struct iio_trigger *trig, s64 time)
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{
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int i;
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if (!trig->use_count)
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for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++)
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if (trig->subirqs[i].enabled) {
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trig->use_count++;
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if (!atomic_read(&trig->use_count)) {
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atomic_set(&trig->use_count, CONFIG_IIO_CONSUMERS_PER_TRIGGER);
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for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++) {
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if (trig->subirqs[i].enabled)
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handle_nested_irq(trig->subirq_base + i);
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}
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else
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iio_trigger_notify_done(trig);
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}
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}
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}
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EXPORT_SYMBOL(iio_trigger_poll_chained);
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void iio_trigger_notify_done(struct iio_trigger *trig)
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{
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trig->use_count--;
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if (trig->use_count == 0 && trig->ops && trig->ops->try_reenable)
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if (atomic_dec_and_test(&trig->use_count) && trig->ops &&
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trig->ops->try_reenable)
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if (trig->ops->try_reenable(trig))
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/* Missed an interrupt so launch new poll now */
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iio_trigger_poll(trig, 0);
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@ -8,6 +8,7 @@
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*/
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#include <linux/irq.h>
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#include <linux/module.h>
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#include <linux/atomic.h>
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#ifndef _IIO_TRIGGER_H_
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#define _IIO_TRIGGER_H_
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@ -61,7 +62,7 @@ struct iio_trigger {
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struct list_head list;
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struct list_head alloc_list;
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int use_count;
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atomic_t use_count;
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struct irq_chip subirq_chip;
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int subirq_base;
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