Re: [PATCH 3/4] staging:iio:events: Use waitqueue lock to protect event queue

[Jonathan Cameron <jic23@kernel.org>]

On 12/16/2011 05:12 PM, Lars-Peter Clausen wrote:
> Use the waitqueue lock to protect the event queue instead of a custom mutex.
> This has the advantage that we can call the waitqueue operations with the lock
> held, which simplifies the code flow a bit.
Didn't realise this was an option. I'm not finding all that many places
doing this.  Could you point out some examples to compare with?
> 
> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
> ---
>  drivers/staging/iio/industrialio-event.c |   43 ++++++++++++-----------------
>  1 files changed, 18 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/staging/iio/industrialio-event.c b/drivers/staging/iio/industrialio-event.c
> index 50d03bd..ef4943a 100644
> --- a/drivers/staging/iio/industrialio-event.c
> +++ b/drivers/staging/iio/industrialio-event.c
> @@ -34,7 +34,6 @@
>   */
>  struct iio_event_interface {
>  	wait_queue_head_t			wait;
> -	struct mutex				event_list_lock;
>  	DECLARE_KFIFO(det_events, struct iio_event_data, 16);
>  
>  	struct list_head dev_attr_list;
> @@ -49,19 +48,17 @@ int iio_push_event(struct iio_dev *indio_dev, u64 ev_code, s64 timestamp)
>  	int ret = 0;
>  
>  	/* Does anyone care? */
> -	mutex_lock(&ev_int->event_list_lock);
> +	spin_lock(&ev_int->wait.lock);
>  	if (test_bit(IIO_BUSY_BIT_POS, &ev_int->flags)) {
>  
>  		ev.id = ev_code;
>  		ev.timestamp = timestamp;
>  
>  		ret = kfifo_put(&ev_int->det_events, &ev);
> -
> -		mutex_unlock(&ev_int->event_list_lock);
>  		if (ret != 0)
> -			wake_up_interruptible(&ev_int->wait);
> -	} else
> -		mutex_unlock(&ev_int->event_list_lock);
> +			wake_up_locked(&ev_int->wait);
> +	}
> +	spin_unlock(&ev_int->wait.lock);
>  
>  	return ret;
>  }
> @@ -79,28 +76,25 @@ static ssize_t iio_event_chrdev_read(struct file *filep,
>  	if (count < sizeof(struct iio_event_data))
>  		return -EINVAL;
>  
> -	mutex_lock(&ev_int->event_list_lock);
> +	spin_lock(&ev_int->wait.lock);
>  	if (kfifo_is_empty(&ev_int->det_events)) {
>  		if (filep->f_flags & O_NONBLOCK) {
>  			ret = -EAGAIN;
> -			goto error_mutex_unlock;
> +			goto error_unlock;
>  		}
> -		mutex_unlock(&ev_int->event_list_lock);
>  		/* Blocking on device; waiting for something to be there */
> -		ret = wait_event_interruptible(ev_int->wait,
> +		ret = wait_event_interruptible_locked(ev_int->wait,
>  					!kfifo_is_empty(&ev_int->det_events));
>  		if (ret)
> -			goto error_ret;
> +			goto error_unlock;
>  		/* Single access device so no one else can get the data */
> -		mutex_lock(&ev_int->event_list_lock);
>  	}
>  
> -	mutex_unlock(&ev_int->event_list_lock);
>  	ret = kfifo_to_user(&ev_int->det_events, buf, count, &copied);
>  
> -error_mutex_unlock:
> -	mutex_unlock(&ev_int->event_list_lock);
> -error_ret:
> +error_unlock:
> +	spin_unlock(&ev_int->wait.lock);
> +
>  	return ret ? ret : copied;
>  }
>  
> @@ -108,10 +102,10 @@ static int iio_event_chrdev_release(struct inode *inode, struct file *filep)
>  {
>  	struct iio_event_interface *ev_int = filep->private_data;
>  
> -	mutex_lock(&ev_int->event_list_lock);
> +	spin_lock(&ev_int->wait.lock);
>  	clear_bit(IIO_BUSY_BIT_POS, &ev_int->flags);
>  	kfifo_reset_out(&ev_int->det_events);
> -	mutex_unlock(&ev_int->event_list_lock);
> +	spin_unlock(&ev_int->wait.lock);
>  
>  	return 0;
>  }
> @@ -131,18 +125,18 @@ int iio_event_getfd(struct iio_dev *indio_dev)
>  	if (ev_int == NULL)
>  		return -ENODEV;
>  
> -	mutex_lock(&ev_int->event_list_lock);
> +	spin_lock(&ev_int->wait.lock);
>  	if (test_and_set_bit(IIO_BUSY_BIT_POS, &ev_int->flags)) {
> -		mutex_unlock(&ev_int->event_list_lock);
> +		spin_unlock(&ev_int->wait.lock);
>  		return -EBUSY;
>  	}
> -	mutex_unlock(&ev_int->event_list_lock);
> +	spin_unlock(&ev_int->wait.lock);
>  	fd = anon_inode_getfd("iio:event",
>  				&iio_event_chrdev_fileops, ev_int, O_RDONLY);
>  	if (fd < 0) {
> -		mutex_lock(&ev_int->event_list_lock);
> +		spin_lock(&ev_int->wait.lock);
>  		clear_bit(IIO_BUSY_BIT_POS, &ev_int->flags);
> -		mutex_unlock(&ev_int->event_list_lock);
> +		spin_unlock(&ev_int->wait.lock);
>  	}
>  	return fd;
>  }
> @@ -351,7 +345,6 @@ static bool iio_check_for_dynamic_events(struct iio_dev *indio_dev)
>  
>  static void iio_setup_ev_int(struct iio_event_interface *ev_int)
>  {
> -	mutex_init(&ev_int->event_list_lock);
>  	INIT_KFIFO(ev_int->det_events);
>  	init_waitqueue_head(&ev_int->wait);
>  }