Re: [PATCH] iio: events: Make iio_push_event() IRQ context save

[Jonathan Cameron <jic23@kernel.org>]

On 03/07/2013 07:53 PM, Lars-Peter Clausen wrote:
> Currently it is not save to call iio_push_event() from hard IRQ context since
> the IIO event code uses spin_lock()/spin_unlock() and it is not save to mix
> calls to spin_lock()/spin_unlock() from different contexts on the same lock.
> E.g. if the lock is being held in iio_event_chrdev_read() and an interrupts
> kicks in and the interrupt handler calls iio_push_event() we end uo with a
> deadlock.
> 
> This patch updates iio_push_event() to use spin_lock_irqsave()/
> spin_unlock_irqstrestore(), since it can be called from both IRQ and non-IRQ
> context. All other other users of the lock, which are always run in non-IRQ
> context, are updated to spin_lock_irq()/spin_unlock_irq().
> 
> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
I'm assuming a driver using this is coming right up?

Anyhow applied to togreg branch of iio.git
> 
> ---
> As far as I can see all current callers of iio_push_event() run in non-IRQ
> context, so this doesn't need to applied to the fixes branch.
> ---
>  drivers/iio/industrialio-event.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-event.c b/drivers/iio/industrialio-event.c
> index 261cae0..10aa9ef8 100644
> --- a/drivers/iio/industrialio-event.c
> +++ b/drivers/iio/industrialio-event.c
> @@ -46,10 +46,11 @@ int iio_push_event(struct iio_dev *indio_dev, u64 ev_code, s64 timestamp)
>  {
>  	struct iio_event_interface *ev_int = indio_dev->event_interface;
>  	struct iio_event_data ev;
> +	unsigned long flags;
>  	int copied;
>  
>  	/* Does anyone care? */
> -	spin_lock(&ev_int->wait.lock);
> +	spin_lock_irqsave(&ev_int->wait.lock, flags);
>  	if (test_bit(IIO_BUSY_BIT_POS, &ev_int->flags)) {
>  
>  		ev.id = ev_code;
> @@ -59,7 +60,7 @@ int iio_push_event(struct iio_dev *indio_dev, u64 ev_code, s64 timestamp)
>  		if (copied != 0)
>  			wake_up_locked_poll(&ev_int->wait, POLLIN);
>  	}
> -	spin_unlock(&ev_int->wait.lock);
> +	spin_unlock_irqrestore(&ev_int->wait.lock, flags);
>  
>  	return 0;
>  }
> @@ -76,10 +77,10 @@ static unsigned int iio_event_poll(struct file *filep,
>  
>  	poll_wait(filep, &ev_int->wait, wait);
>  
> -	spin_lock(&ev_int->wait.lock);
> +	spin_lock_irq(&ev_int->wait.lock);
>  	if (!kfifo_is_empty(&ev_int->det_events))
>  		events = POLLIN | POLLRDNORM;
> -	spin_unlock(&ev_int->wait.lock);
> +	spin_unlock_irq(&ev_int->wait.lock);
>  
>  	return events;
>  }
> @@ -96,14 +97,14 @@ static ssize_t iio_event_chrdev_read(struct file *filep,
>  	if (count < sizeof(struct iio_event_data))
>  		return -EINVAL;
>  
> -	spin_lock(&ev_int->wait.lock);
> +	spin_lock_irq(&ev_int->wait.lock);
>  	if (kfifo_is_empty(&ev_int->det_events)) {
>  		if (filep->f_flags & O_NONBLOCK) {
>  			ret = -EAGAIN;
>  			goto error_unlock;
>  		}
>  		/* Blocking on device; waiting for something to be there */
> -		ret = wait_event_interruptible_locked(ev_int->wait,
> +		ret = wait_event_interruptible_locked_irq(ev_int->wait,
>  					!kfifo_is_empty(&ev_int->det_events));
>  		if (ret)
>  			goto error_unlock;
> @@ -113,7 +114,7 @@ static ssize_t iio_event_chrdev_read(struct file *filep,
>  	ret = kfifo_to_user(&ev_int->det_events, buf, count, &copied);
>  
>  error_unlock:
> -	spin_unlock(&ev_int->wait.lock);
> +	spin_unlock_irq(&ev_int->wait.lock);
>  
>  	return ret ? ret : copied;
>  }
> @@ -122,7 +123,7 @@ static int iio_event_chrdev_release(struct inode *inode, struct file *filep)
>  {
>  	struct iio_event_interface *ev_int = filep->private_data;
>  
> -	spin_lock(&ev_int->wait.lock);
> +	spin_lock_irq(&ev_int->wait.lock);
>  	__clear_bit(IIO_BUSY_BIT_POS, &ev_int->flags);
>  	/*
>  	 * In order to maintain a clean state for reopening,
> @@ -130,7 +131,7 @@ static int iio_event_chrdev_release(struct inode *inode, struct file *filep)
>  	 * any new __iio_push_event calls running.
>  	 */
>  	kfifo_reset_out(&ev_int->det_events);
> -	spin_unlock(&ev_int->wait.lock);
> +	spin_unlock_irq(&ev_int->wait.lock);
>  
>  	return 0;
>  }
> @@ -151,18 +152,18 @@ int iio_event_getfd(struct iio_dev *indio_dev)
>  	if (ev_int == NULL)
>  		return -ENODEV;
>  
> -	spin_lock(&ev_int->wait.lock);
> +	spin_lock_irq(&ev_int->wait.lock);
>  	if (__test_and_set_bit(IIO_BUSY_BIT_POS, &ev_int->flags)) {
> -		spin_unlock(&ev_int->wait.lock);
> +		spin_unlock_irq(&ev_int->wait.lock);
>  		return -EBUSY;
>  	}
> -	spin_unlock(&ev_int->wait.lock);
> +	spin_unlock_irq(&ev_int->wait.lock);
>  	fd = anon_inode_getfd("iio:event",
>  				&iio_event_chrdev_fileops, ev_int, O_RDONLY);
>  	if (fd < 0) {
> -		spin_lock(&ev_int->wait.lock);
> +		spin_lock_irq(&ev_int->wait.lock);
>  		__clear_bit(IIO_BUSY_BIT_POS, &ev_int->flags);
> -		spin_unlock(&ev_int->wait.lock);
> +		spin_unlock_irq(&ev_int->wait.lock);
>  	}
>  	return fd;
>  }
>