[PATCH] drm: Honour O_NONBLOCK on the device for reading events

[Alan Cox]

On Wed,  8 Jun 2011 20:14:01 +0100
Chris Wilson <chris at chris-wilson.co.uk> wrote:

> Otherwise drmHandleEvent will block if accidentally read too often...
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Phillip Haddad <phillip.haddad at gmail.com>
> ---
>  drivers/gpu/drm/drm_fops.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
> index 2ec7d48..279aa95 100644
> --- a/drivers/gpu/drm/drm_fops.c
> +++ b/drivers/gpu/drm/drm_fops.c
> @@ -617,6 +617,9 @@ ssize_t drm_read(struct file *filp, char __user *buffer,
>  	size_t total;
>  	ssize_t ret;
>  
> +	if (filp->f_flags & O_NONBLOCK && list_empty(&file_priv->event_list))
> +		return -EAGAIN;
> +
>  	ret = wait_event_interruptible(file_priv->event_wait,
>  				       !list_empty(&file_priv->event_list));
>  	if (ret < 0)

What happens if someone else empties the list between the test and the
wait_event_interruptible ?