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// 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");
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