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

[Lars-Peter Clausen <lars@metafoo.de>]

On 12/18/2011 10:54 PM, Jonathan Cameron wrote:
> 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?

fs/timerfd.c and also see commit 22c43c81a51
("wait_event_interruptible_locked() interface")

>>
>> 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);
>>  }
> 
>