[PATCH 5.18 0697/1095] coresight: configfs: Fix unload of configurations on module exit

Greg Kroah-Hartman
2022-08-15T22:00:06Z

From: Mike Leach <mike.leach@linaro.org>

[ Upstream commit 199380decc5f9188a9e65676031950f1734aaffe ]

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.

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>
Reviewed-and-tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20220628173004.30002-2-mike.leach@linaro.org
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
.../hwtracing/coresight/coresight-syscfg.c | 104 ++++++++++++++++--
1 file changed, 93 insertions(+), 11 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
index 11850fd8c3b5..17e728ab5c99 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,
@@ -1022,8 +1043,10 @@ 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. */
@@ -1042,6 +1065,13 @@ 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 +1086,73 @@ 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: prior module failed to unload configuration\n");
+ 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 +1160,16 @@ 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)
--
2.35.1