Re: [PATCH v4 1/2] coresight: configfs: Fix unload of configurations on module exit

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Wed, Jun 22, 2022 at 11:16:20AM +0100, Mike Leach wrote:
> Any loaded configurations must be correctly unloaded on coresight module
> exit, or issues can arise with nested locking in the configfs directory
> code if built with CONFIG_LOCKDEP.
> 
> Prior to this patch, the preloaded configuration configfs directory entries
> were being unloaded by the recursive code in
> configfs_unregister_subsystem().
> 
> However, when built with CONFIG_LOCKDEP, this caused a nested lock warning,
> which was not mitigated by the LOCKDEP dependent code in fs/configfs/dir.c
> designed to prevent this, due to the different directory levels for the
> root of the directory being removed.
> 
> As the preloaded (and all other) configurations are registered after
> configfs_register_subsystem(), we now explicitly unload them before the
> call to configfs_unregister_subsystem().
> 
> The new routine cscfg_unload_cfgs_on_exit() iterates through the load
> owner list to unload any remaining configurations that were not unloaded
> by the user before the module exits. This covers both the
> CSCFG_OWNER_PRELOAD and CSCFG_OWNER_MODULE owner types, and will be
> extended to cover future load owner types for CoreSight configurations.
> 
> Applies to coresight/next

The above sentence will end up in the kernel log forever, which is not what we
want.

> 
> Fixes: eb2ec49606c2 ("coresight: syscfg: Update load API for config loadable modules")
> Reported-by: Suzuki Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Mike Leach <mike.leach@linaro.org>
> ---
>  .../hwtracing/coresight/coresight-syscfg.c    | 106 ++++++++++++++++--
>  1 file changed, 95 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
> index 11850fd8c3b5..9cd7d3c91d8e 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> @@ -414,6 +414,27 @@ static void cscfg_remove_owned_csdev_features(struct coresight_device *csdev, vo
>  	}
>  }
>  
> +/*
> + * Unregister all configuration and features from configfs owned by load_owner.
> + * Although this is called without the list mutex being held, it is in the
> + * context of an unload operation which are strictly serialised,
> + * so the lists cannot change during this call.
> + */
> +static void cscfg_fs_unregister_cfgs_feats(void *load_owner)
> +{
> +	struct cscfg_config_desc *config_desc;
> +	struct cscfg_feature_desc *feat_desc;
> +
> +	list_for_each_entry(config_desc, &cscfg_mgr->config_desc_list, item) {
> +		if (config_desc->load_owner == load_owner)
> +			cscfg_configfs_del_config(config_desc);
> +	}
> +	list_for_each_entry(feat_desc, &cscfg_mgr->feat_desc_list, item) {
> +		if (feat_desc->load_owner == load_owner)
> +			cscfg_configfs_del_feature(feat_desc);
> +	}
> +}
> +
>  /*
>   * removal is relatively easy - just remove from all lists, anything that
>   * matches the owner. Memory for the descriptors will be managed by the owner,
> @@ -1022,10 +1043,13 @@ struct device *cscfg_device(void)
>  /* Must have a release function or the kernel will complain on module unload */
>  static void cscfg_dev_release(struct device *dev)
>  {
> +	mutex_lock(&cscfg_mutex);
>  	kfree(cscfg_mgr);
>  	cscfg_mgr = NULL;
> +	mutex_unlock(&cscfg_mutex);
>  }
>  
> +
>  /* a device is needed to "own" some kernel elements such as sysfs entries.  */
>  static int cscfg_create_device(void)
>  {
> @@ -1042,6 +1066,13 @@ static int cscfg_create_device(void)
>  	if (!cscfg_mgr)
>  		goto create_dev_exit_unlock;
>  
> +	/* initialise the cscfg_mgr structure */
> +	INIT_LIST_HEAD(&cscfg_mgr->csdev_desc_list);
> +	INIT_LIST_HEAD(&cscfg_mgr->feat_desc_list);
> +	INIT_LIST_HEAD(&cscfg_mgr->config_desc_list);
> +	INIT_LIST_HEAD(&cscfg_mgr->load_order_list);
> +	atomic_set(&cscfg_mgr->sys_active_cnt, 0);
> +
>  	/* setup the device */
>  	dev = cscfg_device();
>  	dev->release = cscfg_dev_release;
> @@ -1056,17 +1087,74 @@ static int cscfg_create_device(void)
>  	return err;
>  }
>  
> -static void cscfg_clear_device(void)
> +/*
> + * Loading and unloading is generally on user discretion.
> + * If exiting due to coresight module unload, we need to unload any configurations that remain,
> + * before we unregister the configfs intrastructure.
> + *
> + * Do this by walking the load_owner list and taking appropriate action, depending on the load
> + * owner type.
> + */
> +static void cscfg_unload_cfgs_on_exit(void)
>  {
> -	struct cscfg_config_desc *cfg_desc;
> +	struct cscfg_load_owner_info *owner_info = NULL;
>  
> +	/*
> +	 * grab the mutex - even though we are exiting, some configfs files
> +	 * may still be live till we dump them, so ensure list data is
> +	 * protected from a race condition.
> +	 */
>  	mutex_lock(&cscfg_mutex);
> -	list_for_each_entry(cfg_desc, &cscfg_mgr->config_desc_list, item) {
> -		etm_perf_del_symlink_cscfg(cfg_desc);
> +	while (!list_empty(&cscfg_mgr->load_order_list)) {
> +
> +		/* remove in reverse order of loading */
> +		owner_info = list_last_entry(&cscfg_mgr->load_order_list,
> +					     struct cscfg_load_owner_info, item);
> +
> +		/* action according to type */
> +		switch (owner_info->type) {
> +		case CSCFG_OWNER_PRELOAD:
> +			/*
> +			 * preloaded  descriptors are statically allocated in
> +			 * this module - just need to unload dynamic items from
> +			 * csdev lists, and remove from configfs directories.
> +			 */
> +			pr_info("cscfg: unloading preloaded configurations\n");
> +			break;
> +
> +		case  CSCFG_OWNER_MODULE:
> +			/*
> +			 * this is an error - the loadable module must have been unloaded prior
> +			 * to the coresight module unload. Therefore that module has not
> +			 * correctly unloaded configs in its own exit code.
> +			 * Nothing to do other than emit an error string as the static descriptor
> +			 * references we need to unload will have disappeared with the module.
> +			 */
> +			pr_err("cscfg: ERROR - a loadable module failed to "
> +			       "unload configs on exit\n");

This gives me a checkpatch warning.  Please correct and resend a new revision.

Thanks,
Mathieu

> +			goto list_remove;
> +		}
> +
> +		/* remove from configfs - outside the scope of the list mutex */
> +		mutex_unlock(&cscfg_mutex);
> +		cscfg_fs_unregister_cfgs_feats(owner_info);
> +		mutex_lock(&cscfg_mutex);
> +
> +		/* Next unload from csdev lists. */
> +		cscfg_unload_owned_cfgs_feats(owner_info);
> +
> +list_remove:
> +		/* remove from load order list */
> +		list_del(&owner_info->item);
>  	}
> +	mutex_unlock(&cscfg_mutex);
> +}
> +
> +static void cscfg_clear_device(void)
> +{
> +	cscfg_unload_cfgs_on_exit();
>  	cscfg_configfs_release(cscfg_mgr);
>  	device_unregister(cscfg_device());
> -	mutex_unlock(&cscfg_mutex);
>  }
>  
>  /* Initialise system config management API device  */
> @@ -1074,20 +1162,16 @@ int __init cscfg_init(void)
>  {
>  	int err = 0;
>  
> +	/* create the device and init cscfg_mgr */
>  	err = cscfg_create_device();
>  	if (err)
>  		return err;
>  
> +	/* initialise configfs subsystem */
>  	err = cscfg_configfs_init(cscfg_mgr);
>  	if (err)
>  		goto exit_err;
>  
> -	INIT_LIST_HEAD(&cscfg_mgr->csdev_desc_list);
> -	INIT_LIST_HEAD(&cscfg_mgr->feat_desc_list);
> -	INIT_LIST_HEAD(&cscfg_mgr->config_desc_list);
> -	INIT_LIST_HEAD(&cscfg_mgr->load_order_list);
> -	atomic_set(&cscfg_mgr->sys_active_cnt, 0);
> -
>  	/* preload built-in configurations */
>  	err = cscfg_preload(THIS_MODULE);
>  	if (err)
> -- 
> 2.17.1
> 

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