Re: [PATCH v2 4/6] media: subdev: add subdev state locking

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

Hi Tomi,

Thank you for the patch.

On Fri, Dec 17, 2021 at 03:50:20PM +0200, Tomi Valkeinen wrote:
> The V4L2 subdevs have managed without centralized locking for the state
> (previously pad_config), as the try-state is supposedly safe (although I
> believe two TRY ioctls for the same fd would race), and the
> active-state, and its locking, is managed by the drivers internally.
> 
> We now have active-state in a centralized position, and need locking.
> Strictly speaking the locking is only needed for new drivers that use
> the new state, as the current drivers continue behaving as they used to.
> 
> Add a mutex to the struct v4l2_subdev_state, along with a few helper
> functions for locking/unlocking.
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> ---
>  drivers/media/platform/rcar-vin/rcar-v4l2.c |  7 ++-
>  drivers/media/platform/vsp1/vsp1_entity.c   |  8 +++-
>  drivers/media/v4l2-core/v4l2-subdev.c       | 38 +++++++++++++---
>  drivers/staging/media/tegra-video/vi.c      |  8 +++-
>  include/media/v4l2-subdev.h                 | 50 ++++++++++++++++++++-
>  5 files changed, 101 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/media/platform/rcar-vin/rcar-v4l2.c b/drivers/media/platform/rcar-vin/rcar-v4l2.c
> index 5aae01456c04..3759f4619a77 100644
> --- a/drivers/media/platform/rcar-vin/rcar-v4l2.c
> +++ b/drivers/media/platform/rcar-vin/rcar-v4l2.c
> @@ -255,6 +255,7 @@ static int rvin_try_format(struct rvin_dev *vin, u32 which,
>  {
>  	struct v4l2_subdev *sd = vin_to_source(vin);
>  	struct v4l2_subdev_state *sd_state;
> +	static struct lock_class_key key;
>  	struct v4l2_subdev_format format = {
>  		.which = which,
>  		.pad = vin->parallel.source_pad,
> @@ -263,7 +264,11 @@ static int rvin_try_format(struct rvin_dev *vin, u32 which,
>  	u32 width, height;
>  	int ret;
>  
> -	sd_state = __v4l2_subdev_state_alloc(sd);
> +	/*
> +	 * FIXME: Drop this call, drivers are not supposed to use
> +	 * __v4l2_subdev_state_alloc().
> +	 */
> +	sd_state = __v4l2_subdev_state_alloc(sd, "rvin:state->lock", &key);
>  	if (IS_ERR(sd_state))
>  		return PTR_ERR(sd_state);
>  
> diff --git a/drivers/media/platform/vsp1/vsp1_entity.c b/drivers/media/platform/vsp1/vsp1_entity.c
> index 869cadc1468d..a116a3362f9e 100644
> --- a/drivers/media/platform/vsp1/vsp1_entity.c
> +++ b/drivers/media/platform/vsp1/vsp1_entity.c
> @@ -613,6 +613,7 @@ int vsp1_entity_init(struct vsp1_device *vsp1, struct vsp1_entity *entity,
>  		     const char *name, unsigned int num_pads,
>  		     const struct v4l2_subdev_ops *ops, u32 function)
>  {
> +	static struct lock_class_key key;
>  	struct v4l2_subdev *subdev;
>  	unsigned int i;
>  	int ret;
> @@ -675,7 +676,12 @@ int vsp1_entity_init(struct vsp1_device *vsp1, struct vsp1_entity *entity,
>  	 * Allocate the pad configuration to store formats and selection
>  	 * rectangles.
>  	 */
> -	entity->config = __v4l2_subdev_state_alloc(&entity->subdev);
> +	/*
> +	 * FIXME: Drop this call, drivers are not supposed to use
> +	 * __v4l2_subdev_state_alloc().
> +	 */

Feel free to remind me to fix this once the series lands :-)

> +	entity->config = __v4l2_subdev_state_alloc(&entity->subdev,
> +						   "vsp1:config->lock", &key);
>  	if (IS_ERR(entity->config)) {
>  		media_entity_cleanup(&entity->subdev.entity);
>  		return PTR_ERR(entity->config);
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index 779d7ae2262d..5322329d396f 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -27,8 +27,9 @@
>  static int subdev_fh_init(struct v4l2_subdev_fh *fh, struct v4l2_subdev *sd)
>  {
>  	struct v4l2_subdev_state *state;
> +	static struct lock_class_key key;
>  
> -	state = __v4l2_subdev_state_alloc(sd);
> +	state = __v4l2_subdev_state_alloc(sd, "fh->state->lock", &key);
>  	if (IS_ERR(state))
>  		return PTR_ERR(state);
>  
> @@ -914,7 +915,9 @@ int v4l2_subdev_link_validate(struct media_link *link)
>  }
>  EXPORT_SYMBOL_GPL(v4l2_subdev_link_validate);
>  
> -struct v4l2_subdev_state *__v4l2_subdev_state_alloc(struct v4l2_subdev *sd)
> +struct v4l2_subdev_state *
> +__v4l2_subdev_state_alloc(struct v4l2_subdev *sd, const char *lock_name,
> +			  struct lock_class_key *lock_key)
>  {
>  	struct v4l2_subdev_state *state;
>  	int ret;
> @@ -923,6 +926,8 @@ struct v4l2_subdev_state *__v4l2_subdev_state_alloc(struct v4l2_subdev *sd)
>  	if (!state)
>  		return ERR_PTR(-ENOMEM);
>  
> +	__mutex_init(&state->lock, lock_name, lock_key);
> +
>  	if (sd->entity.num_pads) {
>  		state->pads = kvmalloc_array(sd->entity.num_pads,
>  					     sizeof(*state->pads),
> @@ -954,6 +959,8 @@ void __v4l2_subdev_state_free(struct v4l2_subdev_state *state)
>  	if (!state)
>  		return;
>  
> +	mutex_destroy(&state->lock);
> +
>  	kvfree(state->pads);
>  	kfree(state);
>  }
> @@ -988,11 +995,12 @@ void v4l2_subdev_notify_event(struct v4l2_subdev *sd,
>  }
>  EXPORT_SYMBOL_GPL(v4l2_subdev_notify_event);
>  
> -int v4l2_subdev_init_finalize(struct v4l2_subdev *sd)
> +int __v4l2_subdev_init_finalize(struct v4l2_subdev *sd, const char *name,
> +				struct lock_class_key *key)
>  {
>  	struct v4l2_subdev_state *state;
>  
> -	state = __v4l2_subdev_state_alloc(sd);
> +	state = __v4l2_subdev_state_alloc(sd, name, key);
>  	if (IS_ERR(state))
>  		return PTR_ERR(state);
>  
> @@ -1000,7 +1008,7 @@ int v4l2_subdev_init_finalize(struct v4l2_subdev *sd)
>  
>  	return 0;
>  }
> -EXPORT_SYMBOL_GPL(v4l2_subdev_init_finalize);
> +EXPORT_SYMBOL_GPL(__v4l2_subdev_init_finalize);
>  
>  void v4l2_subdev_cleanup(struct v4l2_subdev *sd)
>  {
> @@ -1008,3 +1016,23 @@ void v4l2_subdev_cleanup(struct v4l2_subdev *sd)
>  	sd->active_state = NULL;
>  }
>  EXPORT_SYMBOL_GPL(v4l2_subdev_cleanup);
> +
> +struct v4l2_subdev_state *v4l2_subdev_lock_active_state(struct v4l2_subdev *sd)
> +{
> +	mutex_lock(&sd->active_state->lock);
> +
> +	return sd->active_state;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_subdev_lock_active_state);
> +
> +void v4l2_subdev_lock_state(struct v4l2_subdev_state *state)
> +{
> +	mutex_lock(&state->lock);
> +}
> +EXPORT_SYMBOL_GPL(v4l2_subdev_lock_state);
> +
> +void v4l2_subdev_unlock_state(struct v4l2_subdev_state *state)
> +{
> +	mutex_unlock(&state->lock);
> +}
> +EXPORT_SYMBOL_GPL(v4l2_subdev_unlock_state);
> diff --git a/drivers/staging/media/tegra-video/vi.c b/drivers/staging/media/tegra-video/vi.c
> index b01f19e0f332..b366b56df15c 100644
> --- a/drivers/staging/media/tegra-video/vi.c
> +++ b/drivers/staging/media/tegra-video/vi.c
> @@ -491,6 +491,7 @@ static int __tegra_channel_try_format(struct tegra_vi_channel *chan,
>  				      struct v4l2_pix_format *pix)
>  {
>  	const struct tegra_video_format *fmtinfo;
> +	static struct lock_class_key key;
>  	struct v4l2_subdev *subdev;
>  	struct v4l2_subdev_format fmt;
>  	struct v4l2_subdev_state *sd_state;
> @@ -507,7 +508,12 @@ static int __tegra_channel_try_format(struct tegra_vi_channel *chan,
>  	if (!subdev)
>  		return -ENODEV;
>  
> -	sd_state = __v4l2_subdev_state_alloc(subdev);
> +	/*
> +	 * FIXME: Drop this call, drivers are not supposed to use
> +	 * __v4l2_subdev_state_alloc().
> +	 */
> +	sd_state = __v4l2_subdev_state_alloc(subdev, "tegra:state->lock",
> +					     &key);
>  	if (IS_ERR(sd_state))
>  		return PTR_ERR(sd_state);
>  	/*
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index eddf72768e10..867e19ef80bd 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -658,6 +658,7 @@ struct v4l2_subdev_pad_config {
>  /**
>   * struct v4l2_subdev_state - Used for storing subdev state information.
>   *
> + * @lock: mutex for the state
>   * @pads: &struct v4l2_subdev_pad_config array
>   *
>   * This structure only needs to be passed to the pad op if the 'which' field
> @@ -665,6 +666,8 @@ struct v4l2_subdev_pad_config {
>   * %V4L2_SUBDEV_FORMAT_ACTIVE it is safe to pass %NULL.
>   */
>  struct v4l2_subdev_state {
> +	/* lock for the struct v4l2_subdev_state fields */
> +	struct mutex lock;
>  	struct v4l2_subdev_pad_config *pads;
>  };
>  
> @@ -1157,10 +1160,14 @@ int v4l2_subdev_link_validate(struct media_link *link);
>   * __v4l2_subdev_state_alloc - allocate v4l2_subdev_state
>   *
>   * @sd: pointer to &struct v4l2_subdev for which the state is being allocated.
> + * @lock_name: name of the state lock
> + * @key: lock_class_key for the lock
>   *
>   * Must call __v4l2_subdev_state_free() when state is no longer needed.
>   */
> -struct v4l2_subdev_state *__v4l2_subdev_state_alloc(struct v4l2_subdev *sd);
> +struct v4l2_subdev_state *__v4l2_subdev_state_alloc(struct v4l2_subdev *sd,
> +						    const char *lock_name,
> +						    struct lock_class_key *key);
>  
>  /**
>   * __v4l2_subdev_state_free - free a v4l2_subdev_state
> @@ -1250,7 +1257,16 @@ void v4l2_subdev_notify_event(struct v4l2_subdev *sd,
>   *
>   * The user must call v4l2_subdev_cleanup() when the subdev is being removed.
>   */
> -int v4l2_subdev_init_finalize(struct v4l2_subdev *sd);
> +#define v4l2_subdev_init_finalize(sd)                                          \
> +	({                                                                     \
> +		static struct lock_class_key __key;                            \
> +		const char *name = KBUILD_BASENAME                             \
> +			":" __stringify(__LINE__) ":sd->active_state->lock";   \
> +		__v4l2_subdev_init_finalize(sd, name, &__key);                 \
> +	})
> +
> +int __v4l2_subdev_init_finalize(struct v4l2_subdev *sd, const char *name,
> +				struct lock_class_key *key);
>  
>  /**
>   * v4l2_subdev_cleanup() - Releases the resources needed by the subdevice
> @@ -1275,4 +1291,34 @@ v4l2_subdev_get_active_state(struct v4l2_subdev *sd)
>  	return sd->active_state;
>  }
>  
> +/**
> + * v4l2_subdev_lock_active_state() - Locks and returns the active subdev state
> + *				     for the subdevice
> + * @sd: The subdevice
> + *
> + * Returns the locked active state for the subdevice, or NULL if the subdev
> + * does not support active state.
> + *
> + * The state must be unlocked with v4l2_subdev_unlock_state() after use.
> + */
> +struct v4l2_subdev_state *v4l2_subdev_lock_active_state(struct v4l2_subdev *sd);
> +
> +/**
> + * v4l2_subdev_lock_state() - Locks the subdev state
> + * @state: The subdevice state
> + *
> + * Locks the given subdev state.
> + *
> + * The state must be unlocked with v4l2_subdev_unlock_state() after use.
> + */
> +void v4l2_subdev_lock_state(struct v4l2_subdev_state *state);
> +
> +/**
> + * v4l2_subdev_unlock_state() - Unlocks the subdev state
> + * @state: The subdevice state
> + *
> + * Unlocks the given subdev state.
> + */
> +void v4l2_subdev_unlock_state(struct v4l2_subdev_state *state);
> +
>  #endif

-- 
Regards,

Laurent Pinchart