On 07/16/2013 04:34 PM, Denis CIOCCA wrote:
> Hi Lars,
>
> works fine!
> Tested-by: Denis Ciocca <denis.ciocca@xxxxxx>
>
> Denis
>
> On Tuesday, July 16, 2013 04:28:41 PM Lars-Peter Clausen wrote:
>> 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@xxxxxxxxxx>
Nice clean solution. Thanks.
Applied to the fixes-togreg branch of iio.git.
>> ---
>> Changes since v1:
>> * Set use_count to CONFIG_IIO_CONSUMERS_PER_TRIGGER and call
>> iio_trigger_notify_done for all subirqs that are not enabled to avoid a
>> race which could be triggered if the irq was enabled or disabled while
>> iio_trigger_poll() is running.
>>
>> Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
>> ---
>> drivers/iio/industrialio-trigger.c | 34 ++++++++++++++++++++++------------
>> include/linux/iio/trigger.h | 3 ++-
>> 2 files changed, 24 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/iio/industrialio-trigger.c
>> b/drivers/iio/industrialio-trigger.c index 4d6c7d8..47769ae 100644
>> --- a/drivers/iio/industrialio-trigger.c
>> +++ b/drivers/iio/industrialio-trigger.c
>> @@ -127,12 +127,17 @@ static struct iio_trigger
>> *iio_trigger_find_by_name(const char *name, void iio_trigger_poll(struct
>> iio_trigger *trig, s64 time)
>> {
>> int i;
>> - if (!trig->use_count)
>> - for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++)
>> - if (trig->subirqs[i].enabled) {
>> - trig->use_count++;
>> +
>> + if (!atomic_read(&trig->use_count)) {
>> + atomic_set(&trig->use_count, CONFIG_IIO_CONSUMERS_PER_TRIGGER);
>> +
>> + for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++) {
>> + if (trig->subirqs[i].enabled)
>> generic_handle_irq(trig->subirq_base + i);
>> - }
>> + else
>> + iio_trigger_notify_done(trig);
>> + }
>> + }
>> }
>> EXPORT_SYMBOL(iio_trigger_poll);
>>
>> @@ -146,19 +151,24 @@ EXPORT_SYMBOL(iio_trigger_generic_data_rdy_poll);
>> void iio_trigger_poll_chained(struct iio_trigger *trig, s64 time)
>> {
>> int i;
>> - if (!trig->use_count)
>> - for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++)
>> - if (trig->subirqs[i].enabled) {
>> - trig->use_count++;
>> +
>> + if (!atomic_read(&trig->use_count)) {
>> + atomic_set(&trig->use_count, CONFIG_IIO_CONSUMERS_PER_TRIGGER);
>> +
>> + for (i = 0; i < CONFIG_IIO_CONSUMERS_PER_TRIGGER; i++) {
>> + if (trig->subirqs[i].enabled)
>> handle_nested_irq(trig->subirq_base + i);
>> - }
>> + else
>> + iio_trigger_notify_done(trig);
>> + }
>> + }
>> }
>> EXPORT_SYMBOL(iio_trigger_poll_chained);
>>
>> void iio_trigger_notify_done(struct iio_trigger *trig)
>> {
>> - trig->use_count--;
>> - if (trig->use_count == 0 && trig->ops && trig->ops->try_reenable)
>> + if (atomic_dec_and_test(&trig->use_count) && trig->ops &&
>> + trig->ops->try_reenable)
>> if (trig->ops->try_reenable(trig))
>> /* Missed an interrupt so launch new poll now */
>> iio_trigger_poll(trig, 0);
>> diff --git a/include/linux/iio/trigger.h b/include/linux/iio/trigger.h
>> index 3869c52..369cf2c 100644
>> --- a/include/linux/iio/trigger.h
>> +++ b/include/linux/iio/trigger.h
>> @@ -8,6 +8,7 @@
>> */
>> #include <linux/irq.h>
>> #include <linux/module.h>
>> +#include <linux/atomic.h>
>>
>> #ifndef _IIO_TRIGGER_H_
>> #define _IIO_TRIGGER_H_
>> @@ -61,7 +62,7 @@ struct iio_trigger {
>>
>> struct list_head list;
>> struct list_head alloc_list;
>> - int use_count;
>> + atomic_t use_count;
>>
>> struct irq_chip subirq_chip;
>> int subirq_base;--
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