On 04/10/2018 10:21 AM, Tomasz Figa wrote:
> Hi Hans,
>
> On Mon, Apr 9, 2018 at 11:21 PM Hans Verkuil <[email protected]> wrote:
> [snip]
>> +static void media_request_clean(struct media_request *req)
>> +{
>> + struct media_request_object *obj, *obj_safe;
>> +
>> + WARN_ON(req->state != MEDIA_REQUEST_STATE_CLEANING);
>> +
>> + list_for_each_entry_safe(obj, obj_safe, &req->objects, list) {
>> + media_request_object_unbind(obj);
>> + media_request_object_put(obj);
>> + }
>> +
>> + req->num_incomplete_objects = 0;
>> + wake_up_interruptible(&req->poll_wait);
>
> Do we intentionally wake up only one waiter here (as opposed to calling
> wake_up_interruptible_all())?
_all sounds reasonable. I wish there was better (any!) documentation for the
wake_up
calls.
>
>> +}
>> +
>> +static void media_request_release(struct kref *kref)
>> +{
>> + struct media_request *req =
>> + container_of(kref, struct media_request, kref);
>> + struct media_device *mdev = req->mdev;
>> + unsigned long flags;
>> +
>> + dev_dbg(mdev->dev, "request: release %s\n", req->debug_str);
>> +
>> + spin_lock_irqsave(&req->lock, flags);
>> + req->state = MEDIA_REQUEST_STATE_CLEANING;
>> + spin_unlock_irqrestore(&req->lock, flags);
>> +
>> + media_request_clean(req);
>> +
>> + if (mdev->ops->req_free)
>> + mdev->ops->req_free(req);
>> + else
>> + kfree(req);
>> +}
>> +
>> +void media_request_put(struct media_request *req)
>> +{
>> + kref_put(&req->kref, media_request_release);
>> +}
>> +EXPORT_SYMBOL_GPL(media_request_put);
>> +
>> +void media_request_cancel(struct media_request *req)
>> +{
>> + struct media_request_object *obj, *obj_safe;
>> +
>> + if (req->state != MEDIA_REQUEST_STATE_QUEUED)
>> + return;
>
> I can see that media_request_release() guards the state change with
> req->lock. However we access the state here without holding the spinlock.
>
> Also, should we perhaps have MEDIA_REQUEST_STATE_CANCELLED (or maybe just
> reset to MEDIA_REQUEST_STATE_IDLE?), so that we can guard against calling
> this multiple times?
>
> Or perhaps we're expecting this to be called with req_queue_mutex held?
Hmm, I think that the core problem here is how to avoid a request being queued
while the queue is being canceled.
The best and probably only way to do that is to take the req_queue_mutex for
the streamon/off/_vb2_fop_release functions.
I've added locking for this to the v4l2 core and added a WARN_ON_ONCE check
to see if the req_queue_mutex is indeed locked when this function is called.
>
>> +
>> + list_for_each_entry_safe(obj, obj_safe, &req->objects, list)
>> + if (obj->ops->cancel)
>> + obj->ops->cancel(obj);
>> +}
>> +EXPORT_SYMBOL_GPL(media_request_cancel);
> [snip]
>> +void media_request_object_init(struct media_request_object *obj)
>> +{
>> + obj->ops = NULL;
>> + obj->req = NULL;
>> + obj->priv = NULL;
>
> Perhaps it could make sense to pass ops and priv as arguments here? There
> is probably not much value in having a request object with both set to NULL.
>
>> + obj->completed = false;
>> + INIT_LIST_HEAD(&obj->list);
>> + kref_init(&obj->kref);
>> +}
>> +EXPORT_SYMBOL_GPL(media_request_object_init);
>> +
>> +void media_request_object_bind(struct media_request *req,
>> + const struct media_request_object_ops *ops,
>> + void *priv,
>> + struct media_request_object *obj)
>> +{
>> + unsigned long flags;
>> +
>> + if (WARN_ON(!ops->release || !ops->cancel))
>> + return;
>> +
>> + obj->req = req;
>> + obj->ops = ops;
>> + obj->priv = priv;
>
> Ah, I see, they're being set here. I guess it's just the matter of how we
> define the semantics.
>
> I wonder, though, what happens with a media_request_object struct that was
> allocated, initialized, but not bound to a request, because the client
> terminated. We would want to call media_request_object_put(obj), but
> obj->ops would be NULL.
You can only call media_request_object_put(obj) if obj->req != NULL.
I've added a WARN_ON to media_request_object_put() to check that.
>
>> + spin_lock_irqsave(&req->lock, flags);
>> + if (WARN_ON(req->state != MEDIA_REQUEST_STATE_IDLE))
>> + goto unlock;
>> + list_add_tail(&obj->list, &req->objects);
>> + req->num_incomplete_objects++;
>> +unlock:
>> + spin_unlock_irqrestore(&req->lock, flags);
>> +}
>> +EXPORT_SYMBOL_GPL(media_request_object_bind);
>> +
>> +void media_request_object_unbind(struct media_request_object *obj)
>> +{
>> + struct media_request *req = obj->req;
>> + unsigned long flags;
>> + bool completed = false;
>> +
>> + if (!req)
>> + return;
>
> No need for any locking here?
No, but I did add a WARN_ON here. It really shouldn't be called if
req == NULL.
>
>> +
>> + spin_lock_irqsave(&req->lock, flags);
>> + list_del(&obj->list);
>> + obj->req = NULL;
>> +
>> + if (req->state == MEDIA_REQUEST_STATE_COMPLETE ||
>> + req->state == MEDIA_REQUEST_STATE_CLEANING)
>> + goto unlock;
>> +
>> + if (WARN_ON(req->state == MEDIA_REQUEST_STATE_QUEUEING))
>> + goto unlock;
>> +
>> + if (WARN_ON(!req->num_incomplete_objects))
>> + goto unlock;
>> +
>> + req->num_incomplete_objects--;
>> + if (req->state == MEDIA_REQUEST_STATE_QUEUED &&
>> + !req->num_incomplete_objects) {
>> + req->state = MEDIA_REQUEST_STATE_COMPLETE;
>> + completed = true;
>> + wake_up_interruptible(&req->poll_wait);
>
> Is this intentionally waking up only 1 waiter?
>
>> + }
>> +unlock:
>> + spin_unlock_irqrestore(&req->lock, flags);
>> + if (obj->ops->unbind)
>> + obj->ops->unbind(obj);
>> + if (completed)
>> + media_request_put(req);
>> +}
>> +EXPORT_SYMBOL_GPL(media_request_object_unbind);
>> +
>> +void media_request_object_complete(struct media_request_object *obj)
>> +{
>> + struct media_request *req = obj->req;
>> + unsigned long flags;
>> + bool completed = false;
>> +
>> + spin_lock_irqsave(&req->lock, flags);
>> + if (obj->completed)
>> + goto unlock;
>> + obj->completed = true;
>> + if (WARN_ON(!req->num_incomplete_objects) ||
>> + WARN_ON(req->state != MEDIA_REQUEST_STATE_QUEUED))
>> + goto unlock;
>> +
>> + if (!--req->num_incomplete_objects) {
>> + req->state = MEDIA_REQUEST_STATE_COMPLETE;
>> + wake_up_interruptible(&req->poll_wait);
>
> Is this intentionally waking up only 1 waiter?
Changed them all to _all.
>
>> + completed = true;
>> + }
>> +unlock:
>> + spin_unlock_irqrestore(&req->lock, flags);
>> + if (completed)
>> + media_request_put(req);
>> }
>> +EXPORT_SYMBOL_GPL(media_request_object_complete);
>> diff --git a/include/media/media-request.h b/include/media/media-request.h
>> index dae3eccd9aa7..082c3cae04ac 100644
>> --- a/include/media/media-request.h
>> +++ b/include/media/media-request.h
>> @@ -16,7 +16,163 @@
>
>> #include <media/media-device.h>
>
>> +enum media_request_state {
>> + MEDIA_REQUEST_STATE_IDLE,
>> + MEDIA_REQUEST_STATE_QUEUEING,
>> + MEDIA_REQUEST_STATE_QUEUED,
>> + MEDIA_REQUEST_STATE_COMPLETE,
>> + MEDIA_REQUEST_STATE_CLEANING,
>> +};
>> +
>> +struct media_request_object;
>> +
>> +/**
>> + * struct media_request - Media device request
>> + * @mdev: Media device this request belongs to
>> + * @kref: Reference count
>> + * @debug_prefix: Prefix for debug messages (process name:fd)
>
> debug_str?
Hmm, I prefer debug_prefix.
>
>> + * @state: The state of the request
>> + * @objects: List of @struct media_request_object request objects
>> + * @num_objects: The number objects in the request
>> + * @num_completed_objects: The number of completed objects in the request
>
> num_incomplete_objects?
>
>> + * @poll_wait: Wait queue for poll
>> + * @lock: Serializes access to this struct
>
> Does it have to be acquired to access any field?
Used for state, objects, num_incomplete_objects, so pretty much all, yes.
The other fields are either atomic, have their own lock or do not change.
>
>> + */
>> +struct media_request {
>> + struct media_device *mdev;
>> + struct kref kref;
>> + char debug_str[TASK_COMM_LEN + 11];
>> + enum media_request_state state;
>> + struct list_head objects;
>> + unsigned int num_incomplete_objects;
>> + struct wait_queue_head poll_wait;
>> + spinlock_t lock;
>> +};
>> +
>> +#ifdef CONFIG_MEDIA_CONTROLLER
>> +
>> +static inline void media_request_get(struct media_request *req)
>> +{
>> + kref_get(&req->kref);
>> +}
>> +
>> +void media_request_put(struct media_request *req);
>> +void media_request_cancel(struct media_request *req);
>> +
>> int media_request_alloc(struct media_device *mdev,
>> struct media_request_alloc *alloc);
>> +#else
>> +static inline void media_request_get(struct media_request *req)
>> +{
>> +}
>> +
>> +static inline void media_request_put(struct media_request *req)
>> +{
>> +}
>> +
>> +static inline void media_request_cancel(struct media_request *req)
>> +{
>> +}
>> +
>> +#endif
>> +
>
> Documentation. (Disclaimer from cover letter acknowledged, though. Just
> marking.)
>
>> +struct media_request_object_ops {
>> + int (*prepare)(struct media_request_object *object);
>> + void (*unprepare)(struct media_request_object *object);
>> + void (*queue)(struct media_request_object *object);
>> + void (*unbind)(struct media_request_object *object);
>> + void (*cancel)(struct media_request_object *object);
>> + void (*release)(struct media_request_object *object);
>> +};
>> +
>> +/**
>> + * struct media_request_object - An opaque object that belongs to a media
>> + * request
>> + *
>
> ops
>
>> + * @priv: object's priv pointer
>
> req
>
>> + * @list: List entry of the object for @struct media_request
>> + * @kref: Reference count of the object, acquire before releasing
> req->lock
>
> completed
>
>> + *
>> + * An object related to the request. This struct is embedded in the
>> + * larger object data.
>> + */
>> +struct media_request_object {
>> + const struct media_request_object_ops *ops;
>> + void *priv;
>> + struct media_request *req;
>> + struct list_head list;
>> + struct kref kref;
>> + bool completed;
>> +};
>> +
>> +#ifdef CONFIG_MEDIA_CONTROLLER
>> +static inline void media_request_object_get(struct media_request_object
> *obj)
>> +{
>> + kref_get(&obj->kref);
>> +}
>> +
>> +/**
>> + * media_request_object_put - Put a media request object
>> + *
>> + * @obj: The object
>> + *
>> + * Put a media request object. Once all references are gone, the
>> + * object's memory is released.
>> + */
>> +void media_request_object_put(struct media_request_object *obj);
>> +
>> +/**
>> + * media_request_object_init - Initialise a media request object
>> + *
>> + * Initialise a media request object. The object will be released using
> the
>> + * release callback of the ops once it has no references (this function
>> + * initialises references to one).
>> + */
>> +void media_request_object_init(struct media_request_object *obj);
>> +
>> +/**
>> + * media_request_object_bind - Bind a media request object to a request
>> + */
>> +void media_request_object_bind(struct media_request *req,
>> + const struct media_request_object_ops *ops,
>> + void *priv,
>> + struct media_request_object *obj);
>> +
>> +void media_request_object_unbind(struct media_request_object *obj);
>> +
>> +/**
>> + * media_request_object_complete - Mark the media request object as
> complete
>> + */
>> +void media_request_object_complete(struct media_request_object *obj);
>> +#else
>> +static inline void media_request_object_get(struct media_request_object
> *obj)
>> +{
>> +}
>> +
>> +static inline void media_request_object_put(struct media_request_object
> *obj)
>> +{
>> +}
>> +
>> +static inline void media_request_object_init(struct media_request_object
> *obj)
>> +{
>> + obj->ops = NULL;
>> + obj->req = NULL;
>
> Hmm. Do we need to do anything here if !defined(CONFIG_MEDIA_CONTROLLER)?
The object was likely zeroed when this function is called. But it doesn't hurt
to make sure.
Regards,
Hans
