[RFC PATCH 2/8] coresight: syscfg: Update load API for config loadable modules

[Mathieu Poirier]

On Wed, May 12, 2021 at 10:17:46PM +0100, Mike Leach wrote:
> CoreSight configurations and features can be added as kernel loadable
> modules. This patch updates the load owner API to ensure that the module
> cannot be unloaded either:-

Please remove the '-'.  It is not a big issue but you can be sure the various
patch robots will complain.  With that:

Reviewed-by: Mathieu Poirier <mathieu.poirier at linaro.org>

> 1) if the config it supplies is in use
> 2) if the module is not the last in the load order list.
> 
> Signed-off-by: Mike Leach <mike.leach at linaro.org>
> ---
>  .../hwtracing/coresight/coresight-syscfg.c    | 39 ++++++++++++++++++-
>  .../hwtracing/coresight/coresight-syscfg.h    |  1 +
>  2 files changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
> index ab5ec43a9dad..26c1a244c2b1 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> @@ -368,6 +368,26 @@ int cscfg_update_feat_param_val(struct cscfg_feature_desc *feat_desc,
>  	return err;
>  }
>  
> +/*
> + * Conditionally up reference count on owner to prevent unload.
> + *
> + * module loaded configs need to be locked in to prevent premature unload.
> + */
> +static int cscfg_owner_get(struct cscfg_load_owner_info *owner_info)
> +{
> +	if ((owner_info->type == CSCFG_OWNER_MODULE) &&
> +	    (!try_module_get(owner_info->owner_handle)))
> +		return -EINVAL;
> +	return 0;
> +}
> +
> +/* conditionally lower ref count on an owner */
> +static void cscfg_owner_put(struct cscfg_load_owner_info *owner_info)
> +{
> +	if (owner_info->type == CSCFG_OWNER_MODULE)
> +		module_put(owner_info->owner_handle);
> +}
> +
>  static void cscfg_remove_owned_csdev_configs(struct coresight_device *csdev, void *load_owner)
>  {
>  	struct cscfg_config_csdev *config_csdev, *tmp;
> @@ -497,6 +517,14 @@ int cscfg_load_config_sets(struct cscfg_config_desc **config_descs,
>  
>  	/* add the load owner to the load order list */
>  	list_add_tail(&owner_info->item, &cscfg_mgr->load_order_list);
> +	if (!list_is_singular(&cscfg_mgr->load_order_list)) {
> +		/* lock previous item in load order list */
> +		err = cscfg_owner_get(list_prev_entry(owner_info, item));
> +		if (err) {
> +			cscfg_unload_owned_cfgs_feats(owner_info);
> +			list_del(&owner_info->item);
> +		}
> +	}
>  
>  exit_unlock:
>  	mutex_unlock(&cscfg_mutex);
> @@ -547,7 +575,11 @@ int cscfg_unload_config_sets(struct cscfg_load_owner_info *owner_info)
>  	cscfg_unload_owned_cfgs_feats(owner_info);
>  
>  	/* remove from load order list */
> -	list_del(&load_list_item->item);
> +	if (!list_is_singular(&cscfg_mgr->load_order_list)) {
> +		/* unlock previous item in load order list */
> +		cscfg_owner_put(list_prev_entry(owner_info, item));
> +	}
> +	list_del(&owner_info->item);
>  
>  exit_unlock:
>  	mutex_unlock(&cscfg_mutex);
> @@ -737,6 +769,10 @@ int cscfg_activate_config(unsigned long cfg_hash)
>  
>  	list_for_each_entry(config_desc, &cscfg_mgr->config_desc_list, item) {
>  		if ((unsigned long)config_desc->event_ea->var == cfg_hash) {
> +			/* must ensure that config cannot be unloaded in use */
> +			err = cscfg_owner_get(config_desc->load_owner);
> +			if (err)
> +				break;
>  			/*
>  			 * increment the global active count - control changes to
>  			 * active configurations
> @@ -777,6 +813,7 @@ void cscfg_deactivate_config(unsigned long cfg_hash)
>  		if ((unsigned long)config_desc->event_ea->var == cfg_hash) {
>  			atomic_dec(&config_desc->active_cnt);
>  			atomic_dec(&cscfg_mgr->sys_active_cnt);
> +			cscfg_owner_put(config_desc->load_owner);
>  			dev_dbg(cscfg_device(), "Deactivate config %s.\n", config_desc->name);
>  			break;
>  		}
> diff --git a/drivers/hwtracing/coresight/coresight-syscfg.h b/drivers/hwtracing/coresight/coresight-syscfg.h
> index e2b2bdab31aa..1da37874f70f 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.h
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.h
> @@ -61,6 +61,7 @@ struct cscfg_registered_csdev {
>  /* owner types for loading and unloading of config and feature sets */
>  enum cscfg_load_owner_type {
>  	CSCFG_OWNER_PRELOAD,
> +	CSCFG_OWNER_MODULE,
>  };
>  
>  /**
> -- 
> 2.17.1
>