1// SPDX-License-Identifier: GPL-2.0
2// Copyright (C) 2018 Joe Lawrence <joe.lawrence@redhat.com>
3
4#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
5
6#include <linux/module.h>
7#include <linux/kernel.h>
8#include <linux/sched.h>
9#include <linux/workqueue.h>
10#include <linux/delay.h>
11
12/* load/run-time control from sysfs writer  */
13static bool block_transition;
14module_param(block_transition, bool, 0644);
15MODULE_PARM_DESC(block_transition, "block_transition (default=false)");
16
17static void busymod_work_func(struct work_struct *work);
18static DECLARE_WORK(work, busymod_work_func);
19static DECLARE_COMPLETION(busymod_work_started);
20
21static void busymod_work_func(struct work_struct *work)
22{
23	pr_info("%s enter\n", __func__);
24	complete(&busymod_work_started);
25
26	while (READ_ONCE(block_transition)) {
27		/*
28		 * Busy-wait until the sysfs writer has acknowledged a
29		 * blocked transition and clears the flag.
30		 */
31		msleep(20);
32	}
33
34	pr_info("%s exit\n", __func__);
35}
36
37static int test_klp_callbacks_busy_init(void)
38{
39	pr_info("%s\n", __func__);
40	schedule_work(&work);
41
42	/*
43	 * To synchronize kernel messages, hold the init function from
44	 * exiting until the work function's entry message has printed.
45	 */
46	wait_for_completion(&busymod_work_started);
47
48	if (!block_transition) {
49		/*
50		 * Serialize output: print all messages from the work
51		 * function before returning from init().
52		 */
53		flush_work(&work);
54	}
55
56	return 0;
57}
58
59static void test_klp_callbacks_busy_exit(void)
60{
61	WRITE_ONCE(block_transition, false);
62	flush_work(&work);
63	pr_info("%s\n", __func__);
64}
65
66module_init(test_klp_callbacks_busy_init);
67module_exit(test_klp_callbacks_busy_exit);
68MODULE_LICENSE("GPL");
69MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");
70MODULE_DESCRIPTION("Livepatch test: busy target module");
71