tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
fork
Configure Feed
Select the types of activity you want to include in your feed.
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`, etc., with 2 or more processes.
8 *
9 * This is for testing kernel hung_task error messages with various locking
10 * mechanisms (e.g., mutex, semaphore, etc.). Note that this may freeze
11 * your system or cause a panic. Use only for testing purposes.
12 */
13
14#include <linux/debugfs.h>
15#include <linux/delay.h>
16#include <linux/fs.h>
17#include <linux/module.h>
18#include <linux/mutex.h>
19#include <linux/semaphore.h>
20
21#define HUNG_TASK_DIR "hung_task"
22#define HUNG_TASK_MUTEX_FILE "mutex"
23#define HUNG_TASK_SEM_FILE "semaphore"
24#define SLEEP_SECOND 256
25
26static const char dummy_string[] = "This is a dummy string.";
27static DEFINE_MUTEX(dummy_mutex);
28static DEFINE_SEMAPHORE(dummy_sem, 1);
29static struct dentry *hung_task_dir;
30
31/* Mutex-based read function */
32static ssize_t read_dummy_mutex(struct file *file, char __user *user_buf,
33 size_t count, loff_t *ppos)
34{
35 /* Second task waits on mutex, entering uninterruptible sleep */
36 guard(mutex)(&dummy_mutex);
37
38 /* First task sleeps here, interruptible */
39 msleep_interruptible(SLEEP_SECOND * 1000);
40
41 return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
42 sizeof(dummy_string));
43}
44
45/* Semaphore-based read function */
46static ssize_t read_dummy_semaphore(struct file *file, char __user *user_buf,
47 size_t count, loff_t *ppos)
48{
49 /* Second task waits on semaphore, entering uninterruptible sleep */
50 down(&dummy_sem);
51
52 /* First task sleeps here, interruptible */
53 msleep_interruptible(SLEEP_SECOND * 1000);
54
55 up(&dummy_sem);
56
57 return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
58 sizeof(dummy_string));
59}
60
61/* File operations for mutex */
62static const struct file_operations hung_task_mutex_fops = {
63 .read = read_dummy_mutex,
64};
65
66/* File operations for semaphore */
67static const struct file_operations hung_task_sem_fops = {
68 .read = read_dummy_semaphore,
69};
70
71static int __init hung_task_tests_init(void)
72{
73 hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
74 if (IS_ERR(hung_task_dir))
75 return PTR_ERR(hung_task_dir);
76
77 /* Create debugfs files for mutex and semaphore tests */
78 debugfs_create_file(HUNG_TASK_MUTEX_FILE, 0400, hung_task_dir, NULL,
79 &hung_task_mutex_fops);
80 debugfs_create_file(HUNG_TASK_SEM_FILE, 0400, hung_task_dir, NULL,
81 &hung_task_sem_fops);
82
83 return 0;
84}
85
86static void __exit hung_task_tests_exit(void)
87{
88 debugfs_remove_recursive(hung_task_dir);
89}
90
91module_init(hung_task_tests_init);
92module_exit(hung_task_tests_exit);
93
94MODULE_LICENSE("GPL");
95MODULE_AUTHOR("Masami Hiramatsu <mhiramat@kernel.org>");
96MODULE_AUTHOR("Zi Li <amaindex@outlook.com>");
97MODULE_DESCRIPTION("Simple sleep under lock files for testing hung task");