coresight: syscfg: Update load API for config loadable modules

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:
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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mathieu Poirier <[e-mail]>

drivers/hwtracing/coresight/coresight-syscfg.c

···
 	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;
···
 
 	/* 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);
···
 	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);
···
 
 	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
···
 		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;
 		}

drivers/hwtracing/coresight/coresight-syscfg.h

···
 /* owner types for loading and unloading of config and feature sets */
 enum cscfg_load_owner_type {
 	CSCFG_OWNER_PRELOAD,
+	CSCFG_OWNER_MODULE,
 };
 
 /**