hung_task_tests.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * hung_task_tests.c - Sample code for testing hung tasks with mutex,
  4 * semaphore, etc.
  5 *
  6 * Usage: Load this module and read `<debugfs>/hung_task/mutex`,
  7 *        `<debugfs>/hung_task/semaphore`, `<debugfs>/hung_task/rw_semaphore_read`,
  8 *        `<debugfs>/hung_task/rw_semaphore_write`, etc., with 2 or more processes.
  9 *
 10 * This is for testing kernel hung_task error messages with various locking
 11 * mechanisms (e.g., mutex, semaphore, rw_semaphore_read, rw_semaphore_write, etc.).
 12 * Note that this may freeze your system or cause a panic. Use only for testing purposes.
 13 */
 14
 15#include <linux/debugfs.h>
 16#include <linux/delay.h>
 17#include <linux/fs.h>
 18#include <linux/module.h>
 19#include <linux/mutex.h>
 20#include <linux/semaphore.h>
 21#include <linux/rwsem.h>
 22
 23#define HUNG_TASK_DIR			"hung_task"
 24#define HUNG_TASK_MUTEX_FILE		"mutex"
 25#define HUNG_TASK_SEM_FILE		"semaphore"
 26#define HUNG_TASK_RWSEM_READ_FILE	"rw_semaphore_read"
 27#define HUNG_TASK_RWSEM_WRITE_FILE	"rw_semaphore_write"
 28#define SLEEP_SECOND			256
 29
 30static const char dummy_string[] = "This is a dummy string.";
 31static DEFINE_MUTEX(dummy_mutex);
 32static DEFINE_SEMAPHORE(dummy_sem, 1);
 33static DECLARE_RWSEM(dummy_rwsem);
 34static struct dentry *hung_task_dir;
 35
 36/* Mutex-based read function */
 37static ssize_t read_dummy_mutex(struct file *file, char __user *user_buf,
 38				size_t count, loff_t *ppos)
 39{
 40	/* Check if data is already read */
 41	if (*ppos >= sizeof(dummy_string))
 42		return 0;
 43
 44	/* Second task waits on mutex, entering uninterruptible sleep */
 45	guard(mutex)(&dummy_mutex);
 46
 47	/* First task sleeps here, interruptible */
 48	msleep_interruptible(SLEEP_SECOND * 1000);
 49
 50	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
 51				       sizeof(dummy_string));
 52}
 53
 54/* Semaphore-based read function */
 55static ssize_t read_dummy_semaphore(struct file *file, char __user *user_buf,
 56				    size_t count, loff_t *ppos)
 57{
 58	/* Check if data is already read */
 59	if (*ppos >= sizeof(dummy_string))
 60		return 0;
 61
 62	/* Second task waits on semaphore, entering uninterruptible sleep */
 63	down(&dummy_sem);
 64
 65	/* First task sleeps here, interruptible */
 66	msleep_interruptible(SLEEP_SECOND * 1000);
 67
 68	up(&dummy_sem);
 69
 70	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
 71				       sizeof(dummy_string));
 72}
 73
 74/* Read-write semaphore read function */
 75static ssize_t read_dummy_rwsem_read(struct file *file, char __user *user_buf,
 76				     size_t count, loff_t *ppos)
 77{
 78	/* Check if data is already read */
 79	if (*ppos >= sizeof(dummy_string))
 80		return 0;
 81
 82	/* Acquires read lock, allowing concurrent readers but blocks if write lock is held */
 83	down_read(&dummy_rwsem);
 84
 85	/* Sleeps here, potentially triggering hung task detection if lock is held too long */
 86	msleep_interruptible(SLEEP_SECOND * 1000);
 87
 88	up_read(&dummy_rwsem);
 89
 90	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
 91				       sizeof(dummy_string));
 92}
 93
 94/* Read-write semaphore write function */
 95static ssize_t read_dummy_rwsem_write(struct file *file, char __user *user_buf,
 96				      size_t count, loff_t *ppos)
 97{
 98	/* Check if data is already read */
 99	if (*ppos >= sizeof(dummy_string))
100		return 0;
101
102	/* Acquires exclusive write lock, blocking all other readers and writers */
103	down_write(&dummy_rwsem);
104
105	/* Sleeps here, potentially triggering hung task detection if lock is held too long */
106	msleep_interruptible(SLEEP_SECOND * 1000);
107
108	up_write(&dummy_rwsem);
109
110	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
111				       sizeof(dummy_string));
112}
113
114/* File operations for mutex */
115static const struct file_operations hung_task_mutex_fops = {
116	.read = read_dummy_mutex,
117};
118
119/* File operations for semaphore */
120static const struct file_operations hung_task_sem_fops = {
121	.read = read_dummy_semaphore,
122};
123
124/* File operations for rw_semaphore read */
125static const struct file_operations hung_task_rwsem_read_fops = {
126	.read = read_dummy_rwsem_read,
127};
128
129/* File operations for rw_semaphore write */
130static const struct file_operations hung_task_rwsem_write_fops = {
131	.read = read_dummy_rwsem_write,
132};
133
134static int __init hung_task_tests_init(void)
135{
136	hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
137	if (IS_ERR(hung_task_dir))
138		return PTR_ERR(hung_task_dir);
139
140	/* Create debugfs files for mutex and semaphore tests */
141	debugfs_create_file(HUNG_TASK_MUTEX_FILE, 0400, hung_task_dir, NULL,
142			    &hung_task_mutex_fops);
143	debugfs_create_file(HUNG_TASK_SEM_FILE, 0400, hung_task_dir, NULL,
144			    &hung_task_sem_fops);
145	debugfs_create_file(HUNG_TASK_RWSEM_READ_FILE, 0400, hung_task_dir, NULL,
146			    &hung_task_rwsem_read_fops);
147	debugfs_create_file(HUNG_TASK_RWSEM_WRITE_FILE, 0400, hung_task_dir, NULL,
148			    &hung_task_rwsem_write_fops);
149
150	return 0;
151}
152
153static void __exit hung_task_tests_exit(void)
154{
155	debugfs_remove_recursive(hung_task_dir);
156}
157
158module_init(hung_task_tests_init);
159module_exit(hung_task_tests_exit);
160
161MODULE_LICENSE("GPL");
162MODULE_AUTHOR("Masami Hiramatsu <mhiramat@kernel.org>");
163MODULE_AUTHOR("Zi Li <amaindex@outlook.com>");
164MODULE_DESCRIPTION("Simple sleep under lock files for testing hung task");