[PATCH] drm: Wake up next in drm_read() chain if we are forced to putback the event

[Daniel Vetter]

On Fri, Aug 04, 2017 at 09:23:28AM +0100, Chris Wilson wrote:
> After an event is sent, we try to copy it into the user buffer of the
> first waiter in drm_read() and if the user buffer doesn't have enough
> room we put it back onto the list. However, we didn't wake up any
> subsequent waiter, so that event may sit on the list until either a new
> vblank event is sent or a new waiter appears. Rare, but in the worst
> case may lead to a stuck process.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>

New subtestcase in igt at drm_read?
-Daniel

> ---
>  drivers/gpu/drm/drm_file.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index 59b75a974357..7e6db9f7a058 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -524,6 +524,7 @@ ssize_t drm_read(struct file *filp, char __user *buffer,
>  				file_priv->event_space -= length;
>  				list_add(&e->link, &file_priv->event_list);
>  				spin_unlock_irq(&dev->event_lock);
> +				wake_up_interruptible(&file_priv->event_wait);
>  				break;
>  			}
>  
> -- 
> 2.13.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch