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

["J.I. Cameron" <jic23@xxxxxxxxx>]

On Dec 19 2011, Lars-Peter Clausen wrote:

> 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")
Looks 'by the book' so fine with me (and Greg signed off
on that patch so it should catch him by suprise!)
> > > Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
Acked-by: Jonathan Cameron <jic23@xxxxxxxxxx>
> > > ---
> > >  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);
> > >  }
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