// SPDX-License-Identifier: GPL-2.0-or-later/* * hung_task_mutex.c - Sample code which causes hung task by mutex * * Usage: load this module and read `<debugfs>/hung_task/mutex` *        by 2 or more processes. * * This is for testing kernel hung_task error message. * Note that this will make your system freeze and maybe * cause panic. So do not use this except for the test. */ #include <linux/debugfs.h>#include <linux/delay.h>#include <linux/fs.h>#include <linux/module.h>#include <linux/mutex.h> #define HUNG_TASK_DIR   "hung_task"#define HUNG_TASK_FILE  "mutex"#define SLEEP_SECOND 256 static const char dummy_string[] = "This is a dummy string.";static DEFINE_MUTEX(dummy_mutex);static struct dentry *hung_task_dir; static ssize_t read_dummy(struct file *file, char __user *user_buf,			  size_t count, loff_t *ppos){	/* If the second task waits on the lock, it is uninterruptible sleep. */	guard(mutex)(&dummy_mutex); 	/* When the first task sleep here, it is interruptible. */	msleep_interruptible(SLEEP_SECOND * 1000); 	return simple_read_from_buffer(user_buf, count, ppos,				dummy_string, sizeof(dummy_string));} static const struct file_operations hung_task_fops = {	.read = read_dummy,}; static int __init hung_task_sample_init(void){	hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);	if (IS_ERR(hung_task_dir))		return PTR_ERR(hung_task_dir); 	debugfs_create_file(HUNG_TASK_FILE, 0400, hung_task_dir,			    NULL, &hung_task_fops); 	return 0;} static void __exit hung_task_sample_exit(void){	debugfs_remove_recursive(hung_task_dir);} module_init(hung_task_sample_init);module_exit(hung_task_sample_exit); MODULE_LICENSE("GPL");MODULE_AUTHOR("Masami Hiramatsu");MODULE_DESCRIPTION("Simple sleep under mutex file for testing hung task");