On 2018-05-28 22:26:55 [+0200], Matthias Fuchs wrote:
> Hi,
>
> I updated my modified uio.c code using simple wake queues. See below.
> Blocking read on the uio device is fine. But select() with timeout
> behaves a little strange. I am still digging to find out what happens,
> but it seems that even I should never run into a timeout in my test application,
> the event_count of two consecutive select()/read() pairs is not advanced by one.
>
> So is my implementation correct? Does using the normal waitqueue in this
> manner satisfy uio_poll(). So in my case irq_flags has IRQF_NO_THREAD always set. This means
> idev->wait never gets a wake_up_interruptible().
>
> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> index bcc1fc0..779dcaf 100644
> --- a/drivers/uio/uio.c
> +++ b/drivers/uio/uio.c
> @@ -25,6 +25,7 @@
> #include <linux/kobject.h>
> #include <linux/cdev.h>
> #include <linux/uio_driver.h>
> +#include <linux/swait.h>
>
> #define UIO_MAX_DEVICES (1U << MINORBITS)
>
> @@ -394,8 +395,12 @@ void uio_event_notify(struct uio_info *info)
> struct uio_device *idev = info->uio_dev;
>
> atomic_inc(&idev->event);
> - wake_up_interruptible(&idev->wait);
> - kill_fasync(&idev->async_queue, SIGIO, POLL_IN);
> + if (idev->info->irq_flags & IRQF_NO_THREAD) {
> + swake_up_locked(&idev->swait);
you want swake_up().
> + } else {
> + wake_up_interruptible(&idev->wait);
> + kill_fasync(&idev->async_queue, SIGIO, POLL_IN);
also you need do this if you have someone is in poll(). You could the
upper part in the primary handler this in the threaded handler.
> + }
> }
> EXPORT_SYMBOL_GPL(uio_event_notify);
>
> @@ -508,6 +513,7 @@ static ssize_t uio_read(struct file *filep, char __user *buf,
> struct uio_listener *listener = filep->private_data;
> struct uio_device *idev = listener->dev;
> DECLARE_WAITQUEUE(wait, current);
> + DECLARE_SWAITQUEUE(swait);
> ssize_t retval;
> s32 event_count;
>
> @@ -520,11 +526,10 @@ static ssize_t uio_read(struct file *filep, char __user *buf,
> add_wait_queue(&idev->wait, &wait);
>
> do {
> - set_current_state(TASK_INTERRUPTIBLE);
> + prepare_to_swait(&idev->swait, &swait, TASK_INTERRUPTIBLE);
>
> event_count = atomic_read(&idev->event);
> if (event_count != listener->event_count) {
> - __set_current_state(TASK_RUNNING);
> if (copy_to_user(buf, &event_count, count))
> retval = -EFAULT;
> else {
> @@ -546,7 +551,7 @@ static ssize_t uio_read(struct file *filep, char __user *buf,
> schedule();
> } while (1);
>
> - __set_current_state(TASK_RUNNING);
> + finish_swait(&idev->swait, &swait);
> remove_wait_queue(&idev->wait, &wait);
and ->wait isn't used in ->read() anymore, right? Just in ->poll(). If
so it could go.
> return retval;
> @@ -814,6 +819,7 @@ int __uio_register_device(struct module *owner,
> idev->owner = owner;
> idev->info = info;
> init_waitqueue_head(&idev->wait);
> + init_swait_queue_head(&idev->swait);
> atomic_set(&idev->event, 0);
>
> ret = uio_get_minor(idev);
>
>
> Cheers,
> Matthias
Sebastian
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