Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[mirror_ubuntu-bionic-kernel.git] / lib / test_kmod.c

/*
 * kmod stress test driver
 *
 * Copyright (C) 2017 Luis R. Rodriguez <mcgrof@kernel.org>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or at your option any
 * later version; or, when distributed separately from the Linux kernel or
 * when incorporated into other software packages, subject to the following
 * license:
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of copyleft-next (version 0.3.1 or later) as published
 * at http://copyleft-next.org/.
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

/*
 * This driver provides an interface to trigger and test the kernel's
 * module loader through a series of configurations and a few triggers.
 * To test this driver use the following script as root:
 *
 * tools/testing/selftests/kmod/kmod.sh --help
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kmod.h>
#include <linux/printk.h>
#include <linux/kthread.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/device.h>

#define TEST_START_NUM_THREADS  50
#define TEST_START_DRIVER       "test_module"
#define TEST_START_TEST_FS      "xfs"
#define TEST_START_TEST_CASE    TEST_KMOD_DRIVER


static bool force_init_test = false;
module_param(force_init_test, bool_enable_only, 0644);
MODULE_PARM_DESC(force_init_test,
                 "Force kicking a test immediately after driver loads");

/*
 * For device allocation / registration
 */
static DEFINE_MUTEX(reg_dev_mutex);
static LIST_HEAD(reg_test_devs);

/*
 * num_test_devs actually represents the *next* ID of the next
 * device we will allow to create.
 */
static int num_test_devs;

/**
 * enum kmod_test_case - linker table test case
 *
 * If you add a  test case, please be sure to review if you need to se
 * @need_mod_put for your tests case.
 *
 * @TEST_KMOD_DRIVER: stress tests request_module()
 * @TEST_KMOD_FS_TYPE: stress tests get_fs_type()
 */
enum kmod_test_case {
        __TEST_KMOD_INVALID = 0,

        TEST_KMOD_DRIVER,
        TEST_KMOD_FS_TYPE,

        __TEST_KMOD_MAX,
};

struct test_config {
        char *test_driver;
        char *test_fs;
        unsigned int num_threads;
        enum kmod_test_case test_case;
        int test_result;
};

struct kmod_test_device;

/**
 * kmod_test_device_info - thread info
 *
 * @ret_sync: return value if request_module() is used, sync request for
 *      @TEST_KMOD_DRIVER
 * @fs_sync: return value of get_fs_type() for @TEST_KMOD_FS_TYPE
 * @thread_idx: thread ID
 * @test_dev: test device test is being performed under
 * @need_mod_put: Some tests (get_fs_type() is one) requires putting the module
 *      (module_put(fs_sync->owner)) when done, otherwise you will not be able
 *      to unload the respective modules and re-test. We use this to keep
 *      accounting of when we need this and to help out in case we need to
 *      error out and deal with module_put() on error.
 */
struct kmod_test_device_info {
        int ret_sync;
        struct file_system_type *fs_sync;
        struct task_struct *task_sync;
        unsigned int thread_idx;
        struct kmod_test_device *test_dev;
        bool need_mod_put;
};

/**
 * kmod_test_device - test device to help test kmod
 *
 * @dev_idx: unique ID for test device
 * @config: configuration for the test
 * @misc_dev: we use a misc device under the hood
 * @dev: pointer to misc_dev's own struct device
 * @config_mutex: protects configuration of test
 * @trigger_mutex: the test trigger can only be fired once at a time
 * @thread_lock: protects @done count, and the @info per each thread
 * @done: number of threads which have completed or failed
 * @test_is_oom: when we run out of memory, use this to halt moving forward
 * @kthreads_done: completion used to signal when all work is done
 * @list: needed to be part of the reg_test_devs
 * @info: array of info for each thread
 */
struct kmod_test_device {
        int dev_idx;
        struct test_config config;
        struct miscdevice misc_dev;
        struct device *dev;
        struct mutex config_mutex;
        struct mutex trigger_mutex;
        struct mutex thread_mutex;

        unsigned int done;

        bool test_is_oom;
        struct completion kthreads_done;
        struct list_head list;

        struct kmod_test_device_info *info;
};

static const char *test_case_str(enum kmod_test_case test_case)
{
        switch (test_case) {
        case TEST_KMOD_DRIVER:
                return "TEST_KMOD_DRIVER";
        case TEST_KMOD_FS_TYPE:
                return "TEST_KMOD_FS_TYPE";
        default:
                return "invalid";
        }
}

static struct miscdevice *dev_to_misc_dev(struct device *dev)
{
        return dev_get_drvdata(dev);
}

static struct kmod_test_device *misc_dev_to_test_dev(struct miscdevice *misc_dev)
{
        return container_of(misc_dev, struct kmod_test_device, misc_dev);
}

static struct kmod_test_device *dev_to_test_dev(struct device *dev)
{
        struct miscdevice *misc_dev;

        misc_dev = dev_to_misc_dev(dev);

        return misc_dev_to_test_dev(misc_dev);
}

/* Must run with thread_mutex held */
static void kmod_test_done_check(struct kmod_test_device *test_dev,
                                 unsigned int idx)
{
        struct test_config *config = &test_dev->config;

        test_dev->done++;
        dev_dbg(test_dev->dev, "Done thread count: %u\n", test_dev->done);

        if (test_dev->done == config->num_threads) {
                dev_info(test_dev->dev, "Done: %u threads have all run now\n",
                         test_dev->done);
                dev_info(test_dev->dev, "Last thread to run: %u\n", idx);
                complete(&test_dev->kthreads_done);
        }
}

static void test_kmod_put_module(struct kmod_test_device_info *info)
{
        struct kmod_test_device *test_dev = info->test_dev;
        struct test_config *config = &test_dev->config;

        if (!info->need_mod_put)
                return;

        switch (config->test_case) {
        case TEST_KMOD_DRIVER:
                break;
        case TEST_KMOD_FS_TYPE:
                if (info && info->fs_sync && info->fs_sync->owner)
                        module_put(info->fs_sync->owner);
                break;
        default:
                BUG();
        }

        info->need_mod_put = true;
}

static int run_request(void *data)
{
        struct kmod_test_device_info *info = data;
        struct kmod_test_device *test_dev = info->test_dev;
        struct test_config *config = &test_dev->config;

        switch (config->test_case) {
        case TEST_KMOD_DRIVER:
                info->ret_sync = request_module("%s", config->test_driver);
                break;
        case TEST_KMOD_FS_TYPE:
                info->fs_sync = get_fs_type(config->test_fs);
                info->need_mod_put = true;
                break;
        default:
                /* __trigger_config_run() already checked for test sanity */
                BUG();
                return -EINVAL;
        }

        dev_dbg(test_dev->dev, "Ran thread %u\n", info->thread_idx);

        test_kmod_put_module(info);

        mutex_lock(&test_dev->thread_mutex);
        info->task_sync = NULL;
        kmod_test_done_check(test_dev, info->thread_idx);
        mutex_unlock(&test_dev->thread_mutex);

        return 0;
}

static int tally_work_test(struct kmod_test_device_info *info)
{
        struct kmod_test_device *test_dev = info->test_dev;
        struct test_config *config = &test_dev->config;
        int err_ret = 0;

        switch (config->test_case) {
        case TEST_KMOD_DRIVER:
                /*
                 * Only capture errors, if one is found that's
                 * enough, for now.
                 */
                if (info->ret_sync != 0)
                        err_ret = info->ret_sync;
                dev_info(test_dev->dev,
                         "Sync thread %d return status: %d\n",
                         info->thread_idx, info->ret_sync);
                break;
        case TEST_KMOD_FS_TYPE:
                /* For now we make this simple */
                if (!info->fs_sync)
                        err_ret = -EINVAL;
                dev_info(test_dev->dev, "Sync thread %u fs: %s\n",
                         info->thread_idx, info->fs_sync ? config->test_fs :
                         "NULL");
                break;
        default:
                BUG();
        }

        return err_ret;
}

/*
 * XXX: add result option to display if all errors did not match.
 * For now we just keep any error code if one was found.
 *
 * If this ran it means *all* tasks were created fine and we
 * are now just collecting results.
 *
 * Only propagate errors, do not override with a subsequent sucess case.
 */
static void tally_up_work(struct kmod_test_device *test_dev)
{
        struct test_config *config = &test_dev->config;
        struct kmod_test_device_info *info;
        unsigned int idx;
        int err_ret = 0;
        int ret = 0;

        mutex_lock(&test_dev->thread_mutex);

        dev_info(test_dev->dev, "Results:\n");

        for (idx=0; idx < config->num_threads; idx++) {
                info = &test_dev->info[idx];
                ret = tally_work_test(info);
                if (ret)
                        err_ret = ret;
        }

        /*
         * Note: request_module() returns 256 for a module not found even
         * though modprobe itself returns 1.
         */
        config->test_result = err_ret;

        mutex_unlock(&test_dev->thread_mutex);
}

static int try_one_request(struct kmod_test_device *test_dev, unsigned int idx)
{
        struct kmod_test_device_info *info = &test_dev->info[idx];
        int fail_ret = -ENOMEM;

        mutex_lock(&test_dev->thread_mutex);

        info->thread_idx = idx;
        info->test_dev = test_dev;
        info->task_sync = kthread_run(run_request, info, "%s-%u",
                                      KBUILD_MODNAME, idx);

        if (!info->task_sync || IS_ERR(info->task_sync)) {
                test_dev->test_is_oom = true;
                dev_err(test_dev->dev, "Setting up thread %u failed\n", idx);
                info->task_sync = NULL;
                goto err_out;
        } else
                dev_dbg(test_dev->dev, "Kicked off thread %u\n", idx);

        mutex_unlock(&test_dev->thread_mutex);

        return 0;

err_out:
        info->ret_sync = fail_ret;
        mutex_unlock(&test_dev->thread_mutex);

        return fail_ret;
}

static void test_dev_kmod_stop_tests(struct kmod_test_device *test_dev)
{
        struct test_config *config = &test_dev->config;
        struct kmod_test_device_info *info;
        unsigned int i;

        dev_info(test_dev->dev, "Ending request_module() tests\n");

        mutex_lock(&test_dev->thread_mutex);

        for (i=0; i < config->num_threads; i++) {
                info = &test_dev->info[i];
                if (info->task_sync && !IS_ERR(info->task_sync)) {
                        dev_info(test_dev->dev,
                                 "Stopping still-running thread %i\n", i);
                        kthread_stop(info->task_sync);
                }

                /*
                 * info->task_sync is well protected, it can only be
                 * NULL or a pointer to a struct. If its NULL we either
                 * never ran, or we did and we completed the work. Completed
                 * tasks *always* put the module for us. This is a sanity
                 * check -- just in case.
                 */
                if (info->task_sync && info->need_mod_put)
                        test_kmod_put_module(info);
        }

        mutex_unlock(&test_dev->thread_mutex);
}

/*
 * Only wait *iff* we did not run into any errors during all of our thread
 * set up. If run into any issues we stop threads and just bail out with
 * an error to the trigger. This also means we don't need any tally work
 * for any threads which fail.
 */
static int try_requests(struct kmod_test_device *test_dev)
{
        struct test_config *config = &test_dev->config;
        unsigned int idx;
        int ret;
        bool any_error = false;

        for (idx=0; idx < config->num_threads; idx++) {
                if (test_dev->test_is_oom) {
                        any_error = true;
                        break;
                }

                ret = try_one_request(test_dev, idx);
                if (ret) {
                        any_error = true;
                        break;
                }
        }

        if (!any_error) {
                test_dev->test_is_oom = false;
                dev_info(test_dev->dev,
                         "No errors were found while initializing threads\n");
                wait_for_completion(&test_dev->kthreads_done);
                tally_up_work(test_dev);
        } else {
                test_dev->test_is_oom = true;
                dev_info(test_dev->dev,
                         "At least one thread failed to start, stop all work\n");
                test_dev_kmod_stop_tests(test_dev);
                return -ENOMEM;
        }

        return 0;
}

static int run_test_driver(struct kmod_test_device *test_dev)
{
        struct test_config *config = &test_dev->config;

        dev_info(test_dev->dev, "Test case: %s (%u)\n",
                 test_case_str(config->test_case),
                 config->test_case);
        dev_info(test_dev->dev, "Test driver to load: %s\n",
                 config->test_driver);
        dev_info(test_dev->dev, "Number of threads to run: %u\n",
                 config->num_threads);
        dev_info(test_dev->dev, "Thread IDs will range from 0 - %u\n",
                 config->num_threads - 1);

        return try_requests(test_dev);
}

static int run_test_fs_type(struct kmod_test_device *test_dev)
{
        struct test_config *config = &test_dev->config;

        dev_info(test_dev->dev, "Test case: %s (%u)\n",
                 test_case_str(config->test_case),
                 config->test_case);
        dev_info(test_dev->dev, "Test filesystem to load: %s\n",
                 config->test_fs);
        dev_info(test_dev->dev, "Number of threads to run: %u\n",
                 config->num_threads);
        dev_info(test_dev->dev, "Thread IDs will range from 0 - %u\n",
                 config->num_threads - 1);

        return try_requests(test_dev);
}

static ssize_t config_show(struct device *dev,
                           struct device_attribute *attr,
                           char *buf)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;
        int len = 0;

        mutex_lock(&test_dev->config_mutex);

        len += snprintf(buf, PAGE_SIZE,
                        "Custom trigger configuration for: %s\n",
                        dev_name(dev));

        len += snprintf(buf+len, PAGE_SIZE - len,
                        "Number of threads:\t%u\n",
                        config->num_threads);

        len += snprintf(buf+len, PAGE_SIZE - len,
                        "Test_case:\t%s (%u)\n",
                        test_case_str(config->test_case),
                        config->test_case);

        if (config->test_driver)
                len += snprintf(buf+len, PAGE_SIZE - len,
                                "driver:\t%s\n",
                                config->test_driver);
        else
                len += snprintf(buf+len, PAGE_SIZE - len,
                                "driver:\tEMPTY\n");

        if (config->test_fs)
                len += snprintf(buf+len, PAGE_SIZE - len,
                                "fs:\t%s\n",
                                config->test_fs);
        else
                len += snprintf(buf+len, PAGE_SIZE - len,
                                "fs:\tEMPTY\n");

        mutex_unlock(&test_dev->config_mutex);

        return len;
}
static DEVICE_ATTR_RO(config);

/*
 * This ensures we don't allow kicking threads through if our configuration
 * is faulty.
 */
static int __trigger_config_run(struct kmod_test_device *test_dev)
{
        struct test_config *config = &test_dev->config;

        test_dev->done = 0;

        switch (config->test_case) {
        case TEST_KMOD_DRIVER:
                return run_test_driver(test_dev);
        case TEST_KMOD_FS_TYPE:
                return run_test_fs_type(test_dev);
        default:
                dev_warn(test_dev->dev,
                         "Invalid test case requested: %u\n",
                         config->test_case);
                return -EINVAL;
        }
}

static int trigger_config_run(struct kmod_test_device *test_dev)
{
        struct test_config *config = &test_dev->config;
        int ret;

        mutex_lock(&test_dev->trigger_mutex);
        mutex_lock(&test_dev->config_mutex);

        ret = __trigger_config_run(test_dev);
        if (ret < 0)
                goto out;
        dev_info(test_dev->dev, "General test result: %d\n",
                 config->test_result);

        /*
         * We must return 0 after a trigger even unless something went
         * wrong with the setup of the test. If the test setup went fine
         * then userspace must just check the result of config->test_result.
         * One issue with relying on the return from a call in the kernel
         * is if the kernel returns a possitive value using this trigger
         * will not return the value to userspace, it would be lost.
         *
         * By not relying on capturing the return value of tests we are using
         * through the trigger it also us to run tests with set -e and only
         * fail when something went wrong with the driver upon trigger
         * requests.
         */
        ret = 0;

out:
        mutex_unlock(&test_dev->config_mutex);
        mutex_unlock(&test_dev->trigger_mutex);

        return ret;
}

static ssize_t
trigger_config_store(struct device *dev,
                     struct device_attribute *attr,
                     const char *buf, size_t count)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        int ret;

        if (test_dev->test_is_oom)
                return -ENOMEM;

        /* For all intents and purposes we don't care what userspace
         * sent this trigger, we care only that we were triggered.
         * We treat the return value only for caputuring issues with
         * the test setup. At this point all the test variables should
         * have been allocated so typically this should never fail.
         */
        ret = trigger_config_run(test_dev);
        if (unlikely(ret < 0))
                goto out;

        /*
         * Note: any return > 0 will be treated as success
         * and the error value will not be available to userspace.
         * Do not rely on trying to send to userspace a test value
         * return value as possitive return errors will be lost.
         */
        if (WARN_ON(ret > 0))
                return -EINVAL;

        ret = count;
out:
        return ret;
}
static DEVICE_ATTR_WO(trigger_config);

/*
 * XXX: move to kstrncpy() once merged.
 *
 * Users should use kfree_const() when freeing these.
 */
static int __kstrncpy(char **dst, const char *name, size_t count, gfp_t gfp)
{
        *dst = kstrndup(name, count, gfp);
        if (!*dst)
                return -ENOSPC;
        return count;
}

static int config_copy_test_driver_name(struct test_config *config,
                                    const char *name,
                                    size_t count)
{
        return __kstrncpy(&config->test_driver, name, count, GFP_KERNEL);
}


static int config_copy_test_fs(struct test_config *config, const char *name,
                               size_t count)
{
        return __kstrncpy(&config->test_fs, name, count, GFP_KERNEL);
}

static void __kmod_config_free(struct test_config *config)
{
        if (!config)
                return;

        kfree_const(config->test_driver);
        config->test_driver = NULL;

        kfree_const(config->test_fs);
        config->test_driver = NULL;
}

static void kmod_config_free(struct kmod_test_device *test_dev)
{
        struct test_config *config;

        if (!test_dev)
                return;

        config = &test_dev->config;

        mutex_lock(&test_dev->config_mutex);
        __kmod_config_free(config);
        mutex_unlock(&test_dev->config_mutex);
}

static ssize_t config_test_driver_store(struct device *dev,
                                        struct device_attribute *attr,
                                        const char *buf, size_t count)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;
        int copied;

        mutex_lock(&test_dev->config_mutex);

        kfree_const(config->test_driver);
        config->test_driver = NULL;

        copied = config_copy_test_driver_name(config, buf, count);
        mutex_unlock(&test_dev->config_mutex);

        return copied;
}

/*
 * As per sysfs_kf_seq_show() the buf is max PAGE_SIZE.
 */
static ssize_t config_test_show_str(struct mutex *config_mutex,
                                    char *dst,
                                    char *src)
{
        int len;

        mutex_lock(config_mutex);
        len = snprintf(dst, PAGE_SIZE, "%s\n", src);
        mutex_unlock(config_mutex);

        return len;
}

static ssize_t config_test_driver_show(struct device *dev,
                                        struct device_attribute *attr,
                                        char *buf)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;

        return config_test_show_str(&test_dev->config_mutex, buf,
                                    config->test_driver);
}
static DEVICE_ATTR(config_test_driver, 0644, config_test_driver_show,
                   config_test_driver_store);

static ssize_t config_test_fs_store(struct device *dev,
                                    struct device_attribute *attr,
                                    const char *buf, size_t count)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;
        int copied;

        mutex_lock(&test_dev->config_mutex);

        kfree_const(config->test_fs);
        config->test_fs = NULL;

        copied = config_copy_test_fs(config, buf, count);
        mutex_unlock(&test_dev->config_mutex);

        return copied;
}

static ssize_t config_test_fs_show(struct device *dev,
                                   struct device_attribute *attr,
                                   char *buf)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;

        return config_test_show_str(&test_dev->config_mutex, buf,
                                    config->test_fs);
}
static DEVICE_ATTR(config_test_fs, 0644, config_test_fs_show,
                   config_test_fs_store);

static int trigger_config_run_type(struct kmod_test_device *test_dev,
                                   enum kmod_test_case test_case,
                                   const char *test_str)
{
        int copied = 0;
        struct test_config *config = &test_dev->config;

        mutex_lock(&test_dev->config_mutex);

        switch (test_case) {
        case TEST_KMOD_DRIVER:
                kfree_const(config->test_driver);
                config->test_driver = NULL;
                copied = config_copy_test_driver_name(config, test_str,
                                                      strlen(test_str));
                break;
        case TEST_KMOD_FS_TYPE:
                kfree_const(config->test_fs);
                config->test_driver = NULL;
                copied = config_copy_test_fs(config, test_str,
                                             strlen(test_str));
                break;
        default:
                mutex_unlock(&test_dev->config_mutex);
                return -EINVAL;
        }

        config->test_case = test_case;

        mutex_unlock(&test_dev->config_mutex);

        if (copied <= 0 || copied != strlen(test_str)) {
                test_dev->test_is_oom = true;
                return -ENOMEM;
        }

        test_dev->test_is_oom = false;

        return trigger_config_run(test_dev);
}

static void free_test_dev_info(struct kmod_test_device *test_dev)
{
        vfree(test_dev->info);
        test_dev->info = NULL;
}

static int kmod_config_sync_info(struct kmod_test_device *test_dev)
{
        struct test_config *config = &test_dev->config;

        free_test_dev_info(test_dev);
        test_dev->info = vzalloc(config->num_threads *
                                 sizeof(struct kmod_test_device_info));
        if (!test_dev->info)
                return -ENOMEM;

        return 0;
}

/*
 * Old kernels may not have this, if you want to port this code to
 * test it on older kernels.
 */
#ifdef get_kmod_umh_limit
static unsigned int kmod_init_test_thread_limit(void)
{
        return get_kmod_umh_limit();
}
#else
static unsigned int kmod_init_test_thread_limit(void)
{
        return TEST_START_NUM_THREADS;
}
#endif

static int __kmod_config_init(struct kmod_test_device *test_dev)
{
        struct test_config *config = &test_dev->config;
        int ret = -ENOMEM, copied;

        __kmod_config_free(config);

        copied = config_copy_test_driver_name(config, TEST_START_DRIVER,
                                              strlen(TEST_START_DRIVER));
        if (copied != strlen(TEST_START_DRIVER))
                goto err_out;

        copied = config_copy_test_fs(config, TEST_START_TEST_FS,
                                     strlen(TEST_START_TEST_FS));
        if (copied != strlen(TEST_START_TEST_FS))
                goto err_out;

        config->num_threads = kmod_init_test_thread_limit();
        config->test_result = 0;
        config->test_case = TEST_START_TEST_CASE;

        ret = kmod_config_sync_info(test_dev);
        if (ret)
                goto err_out;

        test_dev->test_is_oom = false;

        return 0;

err_out:
        test_dev->test_is_oom = true;
        WARN_ON(test_dev->test_is_oom);

        __kmod_config_free(config);

        return ret;
}

static ssize_t reset_store(struct device *dev,
                           struct device_attribute *attr,
                           const char *buf, size_t count)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        int ret;

        mutex_lock(&test_dev->trigger_mutex);
        mutex_lock(&test_dev->config_mutex);

        ret = __kmod_config_init(test_dev);
        if (ret < 0) {
                ret = -ENOMEM;
                dev_err(dev, "could not alloc settings for config trigger: %d\n",
                       ret);
                goto out;
        }

        dev_info(dev, "reset\n");
        ret = count;

out:
        mutex_unlock(&test_dev->config_mutex);
        mutex_unlock(&test_dev->trigger_mutex);

        return ret;
}
static DEVICE_ATTR_WO(reset);

static int test_dev_config_update_uint_sync(struct kmod_test_device *test_dev,
                                            const char *buf, size_t size,
                                            unsigned int *config,
                                            int (*test_sync)(struct kmod_test_device *test_dev))
{
        int ret;
        unsigned long new;
        unsigned int old_val;

        ret = kstrtoul(buf, 10, &new);
        if (ret)
                return ret;

        if (new > UINT_MAX)
                return -EINVAL;

        mutex_lock(&test_dev->config_mutex);

        old_val = *config;
        *(unsigned int *)config = new;

        ret = test_sync(test_dev);
        if (ret) {
                *(unsigned int *)config = old_val;

                ret = test_sync(test_dev);
                WARN_ON(ret);

                mutex_unlock(&test_dev->config_mutex);
                return -EINVAL;
        }

        mutex_unlock(&test_dev->config_mutex);
        /* Always return full write size even if we didn't consume all */
        return size;
}

static int test_dev_config_update_uint_range(struct kmod_test_device *test_dev,
                                             const char *buf, size_t size,
                                             unsigned int *config,
                                             unsigned int min,
                                             unsigned int max)
{
        int ret;
        unsigned long new;

        ret = kstrtoul(buf, 10, &new);
        if (ret)
                return ret;

        if (new < min || new > max)
                return -EINVAL;

        mutex_lock(&test_dev->config_mutex);
        *config = new;
        mutex_unlock(&test_dev->config_mutex);

        /* Always return full write size even if we didn't consume all */
        return size;
}

static int test_dev_config_update_int(struct kmod_test_device *test_dev,
                                      const char *buf, size_t size,
                                      int *config)
{
        int ret;
        long new;

        ret = kstrtol(buf, 10, &new);
        if (ret)
                return ret;

        if (new < INT_MIN || new > INT_MAX)
                return -EINVAL;

        mutex_lock(&test_dev->config_mutex);
        *config = new;
        mutex_unlock(&test_dev->config_mutex);
        /* Always return full write size even if we didn't consume all */
        return size;
}

static ssize_t test_dev_config_show_int(struct kmod_test_device *test_dev,
                                        char *buf,
                                        int config)
{
        int val;

        mutex_lock(&test_dev->config_mutex);
        val = config;
        mutex_unlock(&test_dev->config_mutex);

        return snprintf(buf, PAGE_SIZE, "%d\n", val);
}

static ssize_t test_dev_config_show_uint(struct kmod_test_device *test_dev,
                                         char *buf,
                                         unsigned int config)
{
        unsigned int val;

        mutex_lock(&test_dev->config_mutex);
        val = config;
        mutex_unlock(&test_dev->config_mutex);

        return snprintf(buf, PAGE_SIZE, "%u\n", val);
}

static ssize_t test_result_store(struct device *dev,
                                 struct device_attribute *attr,
                                 const char *buf, size_t count)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;

        return test_dev_config_update_int(test_dev, buf, count,
                                          &config->test_result);
}

static ssize_t config_num_threads_store(struct device *dev,
                                        struct device_attribute *attr,
                                        const char *buf, size_t count)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;

        return test_dev_config_update_uint_sync(test_dev, buf, count,
                                                &config->num_threads,
                                                kmod_config_sync_info);
}

static ssize_t config_num_threads_show(struct device *dev,
                                       struct device_attribute *attr,
                                       char *buf)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;

        return test_dev_config_show_int(test_dev, buf, config->num_threads);
}
static DEVICE_ATTR(config_num_threads, 0644, config_num_threads_show,
                   config_num_threads_store);

static ssize_t config_test_case_store(struct device *dev,
                                      struct device_attribute *attr,
                                      const char *buf, size_t count)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;

        return test_dev_config_update_uint_range(test_dev, buf, count,
                                                 &config->test_case,
                                                 __TEST_KMOD_INVALID + 1,
                                                 __TEST_KMOD_MAX - 1);
}

static ssize_t config_test_case_show(struct device *dev,
                                     struct device_attribute *attr,
                                     char *buf)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;

        return test_dev_config_show_uint(test_dev, buf, config->test_case);
}
static DEVICE_ATTR(config_test_case, 0644, config_test_case_show,
                   config_test_case_store);

static ssize_t test_result_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        struct kmod_test_device *test_dev = dev_to_test_dev(dev);
        struct test_config *config = &test_dev->config;

        return test_dev_config_show_int(test_dev, buf, config->test_result);
}
static DEVICE_ATTR(test_result, 0644, test_result_show, test_result_store);

#define TEST_KMOD_DEV_ATTR(name)                &dev_attr_##name.attr

static struct attribute *test_dev_attrs[] = {
        TEST_KMOD_DEV_ATTR(trigger_config),
        TEST_KMOD_DEV_ATTR(config),
        TEST_KMOD_DEV_ATTR(reset),

        TEST_KMOD_DEV_ATTR(config_test_driver),
        TEST_KMOD_DEV_ATTR(config_test_fs),
        TEST_KMOD_DEV_ATTR(config_num_threads),
        TEST_KMOD_DEV_ATTR(config_test_case),
        TEST_KMOD_DEV_ATTR(test_result),

        NULL,
};

ATTRIBUTE_GROUPS(test_dev);

static int kmod_config_init(struct kmod_test_device *test_dev)
{
        int ret;

        mutex_lock(&test_dev->config_mutex);
        ret = __kmod_config_init(test_dev);
        mutex_unlock(&test_dev->config_mutex);

        return ret;
}

static struct kmod_test_device *alloc_test_dev_kmod(int idx)
{
        int ret;
        struct kmod_test_device *test_dev;
        struct miscdevice *misc_dev;

        test_dev = vzalloc(sizeof(struct kmod_test_device));
        if (!test_dev)
                goto err_out;

        mutex_init(&test_dev->config_mutex);
        mutex_init(&test_dev->trigger_mutex);
        mutex_init(&test_dev->thread_mutex);

        init_completion(&test_dev->kthreads_done);

        ret = kmod_config_init(test_dev);
        if (ret < 0) {
                pr_err("Cannot alloc kmod_config_init()\n");
                goto err_out_free;
        }

        test_dev->dev_idx = idx;
        misc_dev = &test_dev->misc_dev;

        misc_dev->minor = MISC_DYNAMIC_MINOR;
        misc_dev->name = kasprintf(GFP_KERNEL, "test_kmod%d", idx);
        if (!misc_dev->name) {
                pr_err("Cannot alloc misc_dev->name\n");
                goto err_out_free_config;
        }
        misc_dev->groups = test_dev_groups;

        return test_dev;

err_out_free_config:
        free_test_dev_info(test_dev);
        kmod_config_free(test_dev);
err_out_free:
        vfree(test_dev);
        test_dev = NULL;
err_out:
        return NULL;
}

static void free_test_dev_kmod(struct kmod_test_device *test_dev)
{
        if (test_dev) {
                kfree_const(test_dev->misc_dev.name);
                test_dev->misc_dev.name = NULL;
                free_test_dev_info(test_dev);
                kmod_config_free(test_dev);
                vfree(test_dev);
                test_dev = NULL;
        }
}

static struct kmod_test_device *register_test_dev_kmod(void)
{
        struct kmod_test_device *test_dev = NULL;
        int ret;

        mutex_lock(&reg_dev_mutex);

        /* int should suffice for number of devices, test for wrap */
        if (unlikely(num_test_devs + 1) < 0) {
                pr_err("reached limit of number of test devices\n");
                goto out;
        }

        test_dev = alloc_test_dev_kmod(num_test_devs);
        if (!test_dev)
                goto out;

        ret = misc_register(&test_dev->misc_dev);
        if (ret) {
                pr_err("could not register misc device: %d\n", ret);
                free_test_dev_kmod(test_dev);
                goto out;
        }

        test_dev->dev = test_dev->misc_dev.this_device;
        list_add_tail(&test_dev->list, &reg_test_devs);
        dev_info(test_dev->dev, "interface ready\n");

        num_test_devs++;

out:
        mutex_unlock(&reg_dev_mutex);

        return test_dev;

}

static int __init test_kmod_init(void)
{
        struct kmod_test_device *test_dev;
        int ret;

        test_dev = register_test_dev_kmod();
        if (!test_dev) {
                pr_err("Cannot add first test kmod device\n");
                return -ENODEV;
        }

        /*
         * With some work we might be able to gracefully enable
         * testing with this driver built-in, for now this seems
         * rather risky. For those willing to try have at it,
         * and enable the below. Good luck! If that works, try
         * lowering the init level for more fun.
         */
        if (force_init_test) {
                ret = trigger_config_run_type(test_dev,
                                              TEST_KMOD_DRIVER, "tun");
                if (WARN_ON(ret))
                        return ret;
                ret = trigger_config_run_type(test_dev,
                                              TEST_KMOD_FS_TYPE, "btrfs");
                if (WARN_ON(ret))
                        return ret;
        }

        return 0;
}
late_initcall(test_kmod_init);

static
void unregister_test_dev_kmod(struct kmod_test_device *test_dev)
{
        mutex_lock(&test_dev->trigger_mutex);
        mutex_lock(&test_dev->config_mutex);

        test_dev_kmod_stop_tests(test_dev);

        dev_info(test_dev->dev, "removing interface\n");
        misc_deregister(&test_dev->misc_dev);
        kfree(&test_dev->misc_dev.name);

        mutex_unlock(&test_dev->config_mutex);
        mutex_unlock(&test_dev->trigger_mutex);

        free_test_dev_kmod(test_dev);
}

static void __exit test_kmod_exit(void)
{
        struct kmod_test_device *test_dev, *tmp;

        mutex_lock(&reg_dev_mutex);
        list_for_each_entry_safe(test_dev, tmp, &reg_test_devs, list) {
                list_del(&test_dev->list);
                unregister_test_dev_kmod(test_dev);
        }
        mutex_unlock(&reg_dev_mutex);
}
module_exit(test_kmod_exit);

MODULE_AUTHOR("Luis R. Rodriguez <mcgrof@kernel.org>");
MODULE_LICENSE("GPL");