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SubjectRe: [PATCH] iio: fix sched WARNING "do not call blocking ops when !TASK_RUNNING"
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On 08/04/2016 11:41 AM, Brian Norris wrote:
> On Thu, Aug 04, 2016 at 10:45:39AM +0200, Lars-Peter Clausen wrote:
>>> @@ -132,10 +133,13 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf,
>>> to_wait = min_t(size_t, n / datum_size, rb->watermark);
>>>
>>> do {
>>> - ret = wait_event_interruptible(rb->pollq,
>>> - iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size));
>>> - if (ret)
>>> - return ret;
>>> + add_wait_queue(&rb->pollq, &wait);
>>> + while (!iio_buffer_ready(indio_dev, rb, to_wait,
>>> + n / datum_size)) {
>>> + wait_woken(&wait, TASK_INTERRUPTIBLE,
>>> + MAX_SCHEDULE_TIMEOUT);
>>
>> We loose the ability to break out from this loop by sending a signal to the
>> task. This needs something like
>>
>> if (signal_pending(current)) {
>> ret = -ERESTARTSYS;
>> break;
>> }
>>
>> before the wait_woken()
>
> Sounds good.
>
>> And as a minor improvement I'd also move the
>> add_wait_queue()/remove_wait_queue() outside of the outer loop.
>
> Sure.
>
>> And then
>> just if (!iio_buffer_ready(...)) continue; rather than having the inner
>> loop. This should slightly simplify the flow.
>
> Perhaps I'm not gathering your meaning here, but wouldn't that turn this
> into a spin loop, waiting for iio_buffer_ready()? i.e.:
>
> do {
> if (!iio_buffer_ready(...))
> continue; // we shouldn't just hammer
> // iio_buffer_ready(), should we?
>
> wait_woken(...);
> ...
> };

Hm, right, I didn't think this through.

How about:

do {
if (!indio_dev->info)
return -ENODEV;

if (!iio_buffer_ready(...)) {
if (signal_pending(current)) {
ret = -ERESTARTSYS;
break;
}
wait_woken(...);
continue;
}
...
} while (ret == 0);

And then also drop the if (!indio_dev->info) at the beginning of the function.

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