1// SPDX-License-Identifier: GPL-2.0+
2/*
3 *	SoftDog:	A Software Watchdog Device
4 *
5 *	(c) Copyright 1996 Alan Cox <alan@lxorguk.ukuu.org.uk>,
6 *							All Rights Reserved.
7 *
8 *	Neither Alan Cox nor CymruNet Ltd. admit liability nor provide
9 *	warranty for any of this software. This material is provided
10 *	"AS-IS" and at no charge.
11 *
12 *	(c) Copyright 1995    Alan Cox <alan@lxorguk.ukuu.org.uk>
13 *
14 *	Software only watchdog driver. Unlike its big brother the WDT501P
15 *	driver this won't always recover a failed machine.
16 */
17
18#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
19
20#include <linux/hrtimer.h>
21#include <linux/init.h>
22#include <linux/kernel.h>
23#include <linux/kthread.h>
24#include <linux/module.h>
25#include <linux/moduleparam.h>
26#include <linux/reboot.h>
27#include <linux/types.h>
28#include <linux/watchdog.h>
29#include <linux/workqueue.h>
30
31#define TIMER_MARGIN	60		/* Default is 60 seconds */
32static unsigned int soft_margin = TIMER_MARGIN;	/* in seconds */
33module_param(soft_margin, uint, 0);
34MODULE_PARM_DESC(soft_margin,
35	"Watchdog soft_margin in seconds. (0 < soft_margin < 65536, default="
36					__MODULE_STRING(TIMER_MARGIN) ")");
37
38static bool nowayout = WATCHDOG_NOWAYOUT;
39module_param(nowayout, bool, 0);
40MODULE_PARM_DESC(nowayout,
41		"Watchdog cannot be stopped once started (default="
42				__MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
43
44static int soft_noboot;
45module_param(soft_noboot, int, 0);
46MODULE_PARM_DESC(soft_noboot,
47	"Softdog action, set to 1 to ignore reboots, 0 to reboot (default=0)");
48
49static int soft_panic;
50module_param(soft_panic, int, 0);
51MODULE_PARM_DESC(soft_panic,
52	"Softdog action, set to 1 to panic, 0 to reboot (default=0)");
53
54static char *soft_reboot_cmd;
55module_param(soft_reboot_cmd, charp, 0000);
56MODULE_PARM_DESC(soft_reboot_cmd,
57	"Set reboot command. Emergency reboot takes place if unset");
58
59static bool soft_active_on_boot;
60module_param(soft_active_on_boot, bool, 0000);
61MODULE_PARM_DESC(soft_active_on_boot,
62	"Set to true to active Softdog on boot (default=false)");
63
64static struct hrtimer softdog_ticktock;
65static struct hrtimer softdog_preticktock;
66
67static int reboot_kthread_fn(void *data)
68{
69	kernel_restart(soft_reboot_cmd);
70	return -EPERM; /* Should not reach here */
71}
72
73static void reboot_work_fn(struct work_struct *unused)
74{
75	kthread_run(reboot_kthread_fn, NULL, "softdog_reboot");
76}
77
78static enum hrtimer_restart softdog_fire(struct hrtimer *timer)
79{
80	static bool soft_reboot_fired;
81
82	module_put(THIS_MODULE);
83	if (soft_noboot) {
84		pr_crit("Triggered - Reboot ignored\n");
85	} else if (soft_panic) {
86		pr_crit("Initiating panic\n");
87		panic("Software Watchdog Timer expired");
88	} else {
89		pr_crit("Initiating system reboot\n");
90		if (!soft_reboot_fired && soft_reboot_cmd != NULL) {
91			static DECLARE_WORK(reboot_work, reboot_work_fn);
92			/*
93			 * The 'kernel_restart' is a 'might-sleep' operation.
94			 * Also, executing it in system-wide workqueues blocks
95			 * any driver from using the same workqueue in its
96			 * shutdown callback function. Thus, we should execute
97			 * the 'kernel_restart' in a standalone kernel thread.
98			 * But since starting a kernel thread is also a
99			 * 'might-sleep' operation, so the 'reboot_work' is
100			 * required as a launcher of the kernel thread.
101			 *
102			 * After request the reboot, restart the timer to
103			 * schedule an 'emergency_restart' reboot after
104			 * 'TIMER_MARGIN' seconds. It's because if the softdog
105			 * hangs, it might be because of scheduling issues. And
106			 * if that is the case, both 'schedule_work' and
107			 * 'kernel_restart' may possibly be malfunctional at the
108			 * same time.
109			 */
110			soft_reboot_fired = true;
111			schedule_work(&reboot_work);
112			hrtimer_add_expires_ns(timer,
113					(u64)TIMER_MARGIN * NSEC_PER_SEC);
114
115			return HRTIMER_RESTART;
116		}
117		emergency_restart();
118		pr_crit("Reboot didn't ?????\n");
119	}
120
121	return HRTIMER_NORESTART;
122}
123
124static struct watchdog_device softdog_dev;
125
126static enum hrtimer_restart softdog_pretimeout(struct hrtimer *timer)
127{
128	watchdog_notify_pretimeout(&softdog_dev);
129
130	return HRTIMER_NORESTART;
131}
132
133static int softdog_ping(struct watchdog_device *w)
134{
135	if (!hrtimer_active(&softdog_ticktock))
136		__module_get(THIS_MODULE);
137	hrtimer_start(&softdog_ticktock, ktime_set(w->timeout, 0),
138		      HRTIMER_MODE_REL);
139
140	if (IS_ENABLED(CONFIG_SOFT_WATCHDOG_PRETIMEOUT)) {
141		if (w->pretimeout)
142			hrtimer_start(&softdog_preticktock,
143				      ktime_set(w->timeout - w->pretimeout, 0),
144				      HRTIMER_MODE_REL);
145		else
146			hrtimer_cancel(&softdog_preticktock);
147	}
148
149	return 0;
150}
151
152static int softdog_stop(struct watchdog_device *w)
153{
154	if (hrtimer_cancel(&softdog_ticktock))
155		module_put(THIS_MODULE);
156
157	if (IS_ENABLED(CONFIG_SOFT_WATCHDOG_PRETIMEOUT))
158		hrtimer_cancel(&softdog_preticktock);
159
160	return 0;
161}
162
163static struct watchdog_info softdog_info = {
164	.identity = "Software Watchdog",
165	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
166};
167
168static const struct watchdog_ops softdog_ops = {
169	.owner = THIS_MODULE,
170	.start = softdog_ping,
171	.stop = softdog_stop,
172};
173
174static struct watchdog_device softdog_dev = {
175	.info = &softdog_info,
176	.ops = &softdog_ops,
177	.min_timeout = 1,
178	.max_timeout = 65535,
179	.timeout = TIMER_MARGIN,
180};
181
182static int __init softdog_init(void)
183{
184	int ret;
185
186	watchdog_init_timeout(&softdog_dev, soft_margin, NULL);
187	watchdog_set_nowayout(&softdog_dev, nowayout);
188	watchdog_stop_on_reboot(&softdog_dev);
189
190	hrtimer_init(&softdog_ticktock, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
191	softdog_ticktock.function = softdog_fire;
192
193	if (IS_ENABLED(CONFIG_SOFT_WATCHDOG_PRETIMEOUT)) {
194		softdog_info.options |= WDIOF_PRETIMEOUT;
195		hrtimer_init(&softdog_preticktock, CLOCK_MONOTONIC,
196			     HRTIMER_MODE_REL);
197		softdog_preticktock.function = softdog_pretimeout;
198	}
199
200	if (soft_active_on_boot)
201		softdog_ping(&softdog_dev);
202
203	ret = watchdog_register_device(&softdog_dev);
204	if (ret)
205		return ret;
206
207	pr_info("initialized. soft_noboot=%d soft_margin=%d sec soft_panic=%d (nowayout=%d)\n",
208		soft_noboot, softdog_dev.timeout, soft_panic, nowayout);
209	pr_info("             soft_reboot_cmd=%s soft_active_on_boot=%d\n",
210		soft_reboot_cmd ?: "<not set>", soft_active_on_boot);
211
212	return 0;
213}
214module_init(softdog_init);
215
216static void __exit softdog_exit(void)
217{
218	watchdog_unregister_device(&softdog_dev);
219}
220module_exit(softdog_exit);
221
222MODULE_AUTHOR("Alan Cox");
223MODULE_DESCRIPTION("Software Watchdog Device Driver");
224MODULE_LICENSE("GPL");
225