Re: [PATCH] drm: Clean up pending events in the core

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Daniel,

Thank you for the patch.

On Saturday 09 January 2016 14:28:46 Daniel Vetter wrote:
> There's really no reason to not do so, instead of replicating this
> for every use-case and every driver. Now we can't just nuke the events,
> since that would still mean that all drm_event users would need to know
> when that has happened, since calling e.g. drm_send_event isn't allowed
> any more. Instead just unlink them from the file, and detect this case
> and handle it appropriately in all functions.
> 
> v2: Adjust existing kerneldoc too.
> 
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/drm_fops.c | 35 ++++++++++++++++++++++++++---------
>  include/drm/drmP.h         |  2 ++
>  2 files changed, 28 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
> index d85af1b2a238..d32b24c74e08 100644
> --- a/drivers/gpu/drm/drm_fops.c
> +++ b/drivers/gpu/drm/drm_fops.c
> @@ -264,6 +264,7 @@ static int drm_open_helper(struct file *filp, struct
> drm_minor *minor) INIT_LIST_HEAD(&priv->fbs);
>  	mutex_init(&priv->fbs_lock);
>  	INIT_LIST_HEAD(&priv->blobs);
> +	INIT_LIST_HEAD(&priv->pending_event_list);
>  	INIT_LIST_HEAD(&priv->event_list);
>  	init_waitqueue_head(&priv->event_wait);
>  	priv->event_space = 4096; /* set aside 4k for event buffer */
> @@ -353,18 +354,16 @@ static void drm_events_release(struct drm_file
> *file_priv) {
>  	struct drm_device *dev = file_priv->minor->dev;
>  	struct drm_pending_event *e, *et;
> -	struct drm_pending_vblank_event *v, *vt;
>  	unsigned long flags;
> 
>  	spin_lock_irqsave(&dev->event_lock, flags);
> 
> -	/* Remove pending flips */
> -	list_for_each_entry_safe(v, vt, &dev->vblank_event_list, base.link)
> -		if (v->base.file_priv == file_priv) {
> -			list_del(&v->base.link);
> -			drm_vblank_put(dev, v->pipe);
> -			v->base.destroy(&v->base);
> -		}

Where does this code go ?

> +	/* Unlink pending events */
> +	list_for_each_entry_safe(e, et, &file_priv->pending_event_list,
> +				 pending_link) {
> +		list_del(&e->pending_link);
> +		e->file_priv = NULL;
> +	}
> 
>  	/* Remove unconsumed events */
>  	list_for_each_entry_safe(e, et, &file_priv->event_list, link) {
> @@ -712,6 +711,7 @@ int drm_event_reserve_init(struct drm_device *dev,
>  	file_priv->event_space -= e->length;
> 
>  	p->event = e;
> +	list_add(&p->pending_link, &file_priv->pending_event_list);
>  	p->file_priv = file_priv;
> 
>  	/* we *could* pass this in as arg, but everyone uses kfree: */
> @@ -736,7 +736,10 @@ void drm_event_cancel_free(struct drm_device *dev,
>  {
>  	unsigned long flags;
>  	spin_lock_irqsave(&dev->event_lock, flags);
> -	p->file_priv->event_space += p->event->length;
> +	if (p->file_priv) {
> +		p->file_priv->event_space += p->event->length;
> +		list_del(&p->pending_link);
> +	}
>  	spin_unlock_irqrestore(&dev->event_lock, flags);
>  	p->destroy(p);
>  }
> @@ -750,11 +753,21 @@ EXPORT_SYMBOL(drm_event_cancel_free);
>   * This function sends the event @e, initialized with
> drm_event_reserve_init(),
>   * to its associated userspace DRM file. Callers must already hold
>   * dev->event_lock, see drm_send_event() for the unlocked version.
> + *
> + * Note that the core will take care of unlinking and disarming events when
> the
> + * corresponding DRM file is closed. Drivers need to worry about that and

s/need to/need not/ ?

> can
> + * call this function upon completion of the asynchrnous work

s/asynchrnous/asynchronous/

> unconditionally. */
>  void drm_send_event_locked(struct drm_device *dev, struct drm_pending_event
> *e) {
>  	assert_spin_locked(&dev->event_lock);
> 
> +	if (!e->file_priv) {

I don't think this could happen before this patch as e->file_priv is 
dereferenced below, and I don't see anything in this patch that makes the 
condition possible.

> +		e->destroy(e);
> +		return;
> +	}
> +
> +	list_del(&e->pending_link);
>  	list_add_tail(&e->link,
>  		      &e->file_priv->event_list);
>  	wake_up_interruptible(&e->file_priv->event_wait);
> @@ -769,6 +782,10 @@ EXPORT_SYMBOL(drm_send_event_locked);
>   * This function sends the event @e, initialized with
> drm_event_reserve_init(),
>   * to its associated userspace DRM file. This function acquires
> dev->event_lock,
>   * see drm_send_event_locked() for callers which already hold this lock.
> + *
> + * Note that the core will take care of unlinking and disarming events when
> the
> + * corresponding DRM file is closed. Drivers need to worry about that and

s/need to/need not/ ?

> can
> + * call this function upon completion of the asynchrnous work

s/asynchrnous/asynchronous/

> unconditionally. */
>  void drm_send_event(struct drm_device *dev, struct drm_pending_event *e)
>  {
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index ae73abf5c2cf..3d78a7406d54 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -283,6 +283,7 @@ struct drm_ioctl_desc {
>  struct drm_pending_event {
>  	struct drm_event *event;
>  	struct list_head link;
> +	struct list_head pending_link;
>  	struct drm_file *file_priv;
>  	pid_t pid; /* pid of requester, no guarantee it's valid by the time
>  		      we deliver the event, for tracing only */
> @@ -346,6 +347,7 @@ struct drm_file {
>  	struct list_head blobs;
> 
>  	wait_queue_head_t event_wait;
> +	struct list_head pending_event_list;
>  	struct list_head event_list;
>  	int event_space;

-- 
Regards,

Laurent Pinchart

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