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From: David Lechner <david@lechnology.com>
To: William Breathitt Gray <vilhelm.gray@gmail.com>, jic23@kernel.org
Cc: kamel.bouhara@bootlin.com, gwendal@chromium.org,
	alexandre.belloni@bootlin.com, linux-iio@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com,
	patrick.havelange@essensium.com, fabrice.gasnier@st.com,
	mcoquelin.stm32@gmail.com, alexandre.torgue@st.com
Subject: Re: [PATCH v5 3/5] counter: Add character device interface
Date: Wed, 14 Oct 2020 17:40:44 -0500
Message-ID: <cc1f7e4d-18d1-bc28-8ce3-e3edcd91bcab@lechnology.com> (raw)
In-Reply-To: <00be1fccc672c5207f3b04fe4cc09c29e22641f4.1601170670.git.vilhelm.gray@gmail.com>

On 9/26/20 9:18 PM, William Breathitt Gray wrote:
> +static ssize_t counter_chrdev_read(struct file *filp, char __user *buf,
> +				   size_t len, loff_t *f_ps)
> +{
> +	struct counter_device *const counter = filp->private_data;
> +	int err;
> +	unsigned long flags;
> +	unsigned int copied;
> +
> +	if (len < sizeof(struct counter_event))
> +		return -EINVAL;
> +
> +	do {
> +		if (kfifo_is_empty(&counter->events)) {
> +			if (filp->f_flags & O_NONBLOCK)
> +				return -EAGAIN;
> +
> +			err = wait_event_interruptible(counter->events_wait,
> +					!kfifo_is_empty(&counter->events));
> +			if (err)
> +				return err;
> +		}
> +
> +		raw_spin_lock_irqsave(&counter->events_lock, flags);
> +		err = kfifo_to_user(&counter->events, buf, len, &copied);
> +		raw_spin_unlock_irqrestore(&counter->events_lock, flags);
> +		if (err)
> +			return err;
> +	} while (!copied);
> +
> +	return copied;
> +}

All other uses of kfifo_to_user() I saw use a mutex instead of spin
lock. I don't see a reason for disabling interrupts here.

Example:


static ssize_t iio_event_chrdev_read(struct file *filep,
				     char __user *buf,
				     size_t count,
				     loff_t *f_ps)
{
	struct iio_dev *indio_dev = filep->private_data;
	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
	struct iio_event_interface *ev_int = iio_dev_opaque->event_interface;
	unsigned int copied;
	int ret;

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

	if (count < sizeof(struct iio_event_data))
		return -EINVAL;

	do {
		if (kfifo_is_empty(&ev_int->det_events)) {
			if (filep->f_flags & O_NONBLOCK)
				return -EAGAIN;

			ret = wait_event_interruptible(ev_int->wait,
					!kfifo_is_empty(&ev_int->det_events) ||
					indio_dev->info == NULL);
			if (ret)
				return ret;
			if (indio_dev->info == NULL)
				return -ENODEV;
		}

		if (mutex_lock_interruptible(&ev_int->read_lock))
			return -ERESTARTSYS;
		ret = kfifo_to_user(&ev_int->det_events, buf, count, &copied);
		mutex_unlock(&ev_int->read_lock);

		if (ret)
			return ret;

		/*
		 * If we couldn't read anything from the fifo (a different
		 * thread might have been faster) we either return -EAGAIN if
		 * the file descriptor is non-blocking, otherwise we go back to
		 * sleep and wait for more data to arrive.
		 */
		if (copied == 0 && (filep->f_flags & O_NONBLOCK))
			return -EAGAIN;

	} while (copied == 0);

	return copied;
}

  parent reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-27  2:18 [PATCH v5 0/5] Introduce the Counter " William Breathitt Gray
2020-09-27  2:18 ` [PATCH v5 2/5] docs: counter: Update to reflect sysfs internalization William Breathitt Gray
2020-09-27  2:18 ` [PATCH v5 3/5] counter: Add character device interface William Breathitt Gray
2020-10-14  1:40   ` David Lechner
2020-10-18 16:49     ` William Breathitt Gray
2020-10-20 15:53       ` David Lechner
2020-10-25 12:55         ` William Breathitt Gray
2020-10-25 16:36           ` David Lechner
2020-10-14 17:43   ` David Lechner
2020-10-14 19:05     ` William Breathitt Gray
2020-10-14 22:32       ` David Lechner
2020-10-14 22:40   ` David Lechner [this message]
2020-10-18 16:58     ` William Breathitt Gray
2020-10-20 16:06       ` David Lechner
2020-10-25 13:18         ` William Breathitt Gray
2020-10-25 16:34           ` David Lechner
2020-10-25 17:53             ` William Breathitt Gray
2020-09-27  2:18 ` [PATCH v5 4/5] docs: counter: Document " William Breathitt Gray
2020-10-08  8:09   ` Pavel Machek
2020-10-08 12:28     ` William Breathitt Gray
2020-10-12 17:04       ` David Lechner
2020-10-13 18:58         ` William Breathitt Gray
2020-10-13 19:08           ` David Lechner
2020-10-13 19:27             ` William Breathitt Gray
2020-09-27  2:18 ` [PATCH v5 5/5] counter: 104-quad-8: Add IRQ support for the ACCES 104-QUAD-8 William Breathitt Gray
2020-10-14  0:13   ` David Lechner
2020-10-18 14:50     ` William Breathitt Gray
2020-10-13  0:35 ` [PATCH v5 0/5] Introduce the Counter character device interface David Lechner
2020-10-18 14:14   ` William Breathitt Gray
     [not found] ` <e38f6dc3a08bf2510034334262776a6ed1df8b89.1601170670.git.vilhelm.gray@gmail.com>
2020-10-13  2:15   ` [PATCH v5 1/5] counter: Internalize sysfs interface code David Lechner
2020-10-18 14:49     ` William Breathitt Gray
2020-10-20 15:38       ` David Lechner
2020-10-23 13:12         ` William Breathitt Gray
2020-10-15  1:38   ` David Lechner
2020-10-18 17:00     ` William Breathitt Gray

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