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  */
13 static bool block_transition;
14 module_param(block_transition, bool, 0644);
15 MODULE_PARM_DESC(block_transition, "block_transition (default=false)");
16 
17 static void busymod_work_func(struct work_struct *work);
18 static DECLARE_WORK(work, busymod_work_func);
19 static DECLARE_COMPLETION(busymod_work_started);
20 
busymod_work_func(struct work_struct * work)21 static 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 
test_klp_callbacks_busy_init(void)37 static 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 
test_klp_callbacks_busy_exit(void)59 static 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 
66 module_init(test_klp_callbacks_busy_init);
67 module_exit(test_klp_callbacks_busy_exit);
68 MODULE_LICENSE("GPL");
69 MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");
70 MODULE_DESCRIPTION("Livepatch test: busy target module");
71