drivers/watchdog/softdog.c

   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 */
  32 static unsigned int soft_margin = TIMER_MARGIN; /* in seconds */
  33 module_param(soft_margin, uint, 0);
  34 MODULE_PARM_DESC(soft_margin,
  35         "Watchdog soft_margin in seconds. (0 < soft_margin < 65536, default="
  36                                         __MODULE_STRING(TIMER_MARGIN) ")");
  37
  38 static bool nowayout = WATCHDOG_NOWAYOUT;
  39 module_param(nowayout, bool, 0);
  40 MODULE_PARM_DESC(nowayout,
  41                 "Watchdog cannot be stopped once started (default="
  42                                 __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
  43
  44 static int soft_noboot;
  45 module_param(soft_noboot, int, 0);
  46 MODULE_PARM_DESC(soft_noboot,
  47         "Softdog action, set to 1 to ignore reboots, 0 to reboot (default=0)");
  48
  49 static int soft_panic;
  50 module_param(soft_panic, int, 0);
  51 MODULE_PARM_DESC(soft_panic,
  52         "Softdog action, set to 1 to panic, 0 to reboot (default=0)");
  53
  54 static char *soft_reboot_cmd;
  55 module_param(soft_reboot_cmd, charp, 0000);
  56 MODULE_PARM_DESC(soft_reboot_cmd,
  57         "Set reboot command. Emergency reboot takes place if unset");
  58
  59 static bool soft_active_on_boot;
  60 module_param(soft_active_on_boot, bool, 0000);
  61 MODULE_PARM_DESC(soft_active_on_boot,
  62         "Set to true to active Softdog on boot (default=false)");
  63
  64 static struct hrtimer softdog_ticktock;
  65 static struct hrtimer softdog_preticktock;
  66
  67 static int reboot_kthread_fn(void *data)
  68 {
  69         kernel_restart(soft_reboot_cmd);
  70         return -EPERM; /* Should not reach here */
  71 }
  72
  73 static void reboot_work_fn(struct work_struct *unused)
  74 {
  75         kthread_run(reboot_kthread_fn, NULL, "softdog_reboot");
  76 }
  77
  78 static 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
 124 static struct watchdog_device softdog_dev;
 125
 126 static enum hrtimer_restart softdog_pretimeout(struct hrtimer *timer)
 127 {
 128         watchdog_notify_pretimeout(&softdog_dev);
 129
 130         return HRTIMER_NORESTART;
 131 }
 132
 133 static 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
 152 static 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
 163 static struct watchdog_info softdog_info = {
 164         .identity = "Software Watchdog",
 165         .options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
 166 };
 167
 168 static const struct watchdog_ops softdog_ops = {
 169         .owner = THIS_MODULE,
 170         .start = softdog_ping,
 171         .stop = softdog_stop,
 172 };
 173
 174 static 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
 182 static 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 }
 214 module_init(softdog_init);
 215
 216 static void __exit softdog_exit(void)
 217 {
 218         watchdog_unregister_device(&softdog_dev);
 219 }
 220 module_exit(softdog_exit);
 221
 222 MODULE_AUTHOR("Alan Cox");
 223 MODULE_DESCRIPTION("Software Watchdog Device Driver");
 224 MODULE_LICENSE("GPL");