kernel/softlockup.c

   1 /*
   2  * Detect Soft Lockups
   3  *
   4  * started by Ingo Molnar, Copyright (C) 2005, 2006 Red Hat, Inc.
   5  *
   6  * this code detects soft lockups: incidents in where on a CPU
   7  * the kernel does not reschedule for 10 seconds or more.
   8  */
   9 #include <linux/mm.h>
  10 #include <linux/cpu.h>
  11 #include <linux/nmi.h>
  12 #include <linux/init.h>
  13 #include <linux/delay.h>
  14 #include <linux/freezer.h>
  15 #include <linux/kthread.h>
  16 #include <linux/lockdep.h>
  17 #include <linux/notifier.h>
  18 #include <linux/module.h>
  19 #include <linux/sysctl.h>
  20
  21 #include <asm/irq_regs.h>
  22
  23 static DEFINE_SPINLOCK(print_lock);
  24
  25 static DEFINE_PER_CPU(unsigned long, softlockup_touch_ts); /* touch timestamp */
  26 static DEFINE_PER_CPU(unsigned long, softlockup_print_ts); /* print timestamp */
  27 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
  28 static DEFINE_PER_CPU(bool, softlock_touch_sync);
  29
  30 static int __read_mostly did_panic;
  31 int __read_mostly softlockup_thresh = 60;
  32
  33 /*
  34  * Should we panic (and reboot, if panic_timeout= is set) when a
  35  * soft-lockup occurs:
  36  */
  37 unsigned int __read_mostly softlockup_panic =
  38                                 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  39
  40 static int __init softlockup_panic_setup(char *str)
  41 {
  42         softlockup_panic = simple_strtoul(str, NULL, 0);
  43
  44         return 1;
  45 }
  46 __setup("softlockup_panic=", softlockup_panic_setup);
  47
  48 static int
  49 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
  50 {
  51         did_panic = 1;
  52
  53         return NOTIFY_DONE;
  54 }
  55
  56 static struct notifier_block panic_block = {
  57         .notifier_call = softlock_panic,
  58 };
  59
  60 /*
  61  * Returns seconds, approximately.  We don't need nanosecond
  62  * resolution, and we don't need to waste time with a big divide when
  63  * 2^30ns == 1.074s.
  64  */
  65 static unsigned long get_timestamp(int this_cpu)
  66 {
  67         return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
  68 }
  69
  70 static void __touch_softlockup_watchdog(void)
  71 {
  72         int this_cpu = raw_smp_processor_id();
  73
  74         __raw_get_cpu_var(softlockup_touch_ts) = get_timestamp(this_cpu);
  75 }
  76
  77 void touch_softlockup_watchdog(void)
  78 {
  79         __raw_get_cpu_var(softlockup_touch_ts) = 0;
  80 }
  81 EXPORT_SYMBOL(touch_softlockup_watchdog);
  82
  83 void touch_softlockup_watchdog_sync(void)
  84 {
  85         __raw_get_cpu_var(softlock_touch_sync) = true;
  86         __raw_get_cpu_var(softlockup_touch_ts) = 0;
  87 }
  88
  89 void touch_all_softlockup_watchdogs(void)
  90 {
  91         int cpu;
  92
  93         /* Cause each CPU to re-update its timestamp rather than complain */
  94         for_each_online_cpu(cpu)
  95                 per_cpu(softlockup_touch_ts, cpu) = 0;
  96 }
  97 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
  98
  99 int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
 100                              void __user *buffer,
 101                              size_t *lenp, loff_t *ppos)
 102 {
 103         touch_all_softlockup_watchdogs();
 104         return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 105 }
 106
 107 /*
 108  * This callback runs from the timer interrupt, and checks
 109  * whether the watchdog thread has hung or not:
 110  */
 111 void softlockup_tick(void)
 112 {
 113         int this_cpu = smp_processor_id();
 114         unsigned long touch_ts = per_cpu(softlockup_touch_ts, this_cpu);
 115         unsigned long print_ts;
 116         struct pt_regs *regs = get_irq_regs();
 117         unsigned long now;
 118
 119         /* Is detection switched off? */
 120         if (!per_cpu(softlockup_watchdog, this_cpu) || softlockup_thresh <= 0) {
 121                 /* Be sure we don't false trigger if switched back on */
 122                 if (touch_ts)
 123                         per_cpu(softlockup_touch_ts, this_cpu) = 0;
 124                 return;
 125         }
 126
 127         if (touch_ts == 0) {
 128                 if (unlikely(per_cpu(softlock_touch_sync, this_cpu))) {
 129                         /*
 130                          * If the time stamp was touched atomically
 131                          * make sure the scheduler tick is up to date.
 132                          */
 133                         per_cpu(softlock_touch_sync, this_cpu) = false;
 134                         sched_clock_tick();
 135                 }
 136                 __touch_softlockup_watchdog();
 137                 return;
 138         }
 139
 140         print_ts = per_cpu(softlockup_print_ts, this_cpu);
 141
 142         /* report at most once a second */
 143         if (print_ts == touch_ts || did_panic)
 144                 return;
 145
 146         /* do not print during early bootup: */
 147         if (unlikely(system_state != SYSTEM_RUNNING)) {
 148                 __touch_softlockup_watchdog();
 149                 return;
 150         }
 151
 152         now = get_timestamp(this_cpu);
 153
 154         /*
 155          * Wake up the high-prio watchdog task twice per
 156          * threshold timespan.
 157          */
 158         if (now > touch_ts + softlockup_thresh/2)
 159                 wake_up_process(per_cpu(softlockup_watchdog, this_cpu));
 160
 161         /* Warn about unreasonable delays: */
 162         if (now <= (touch_ts + softlockup_thresh))
 163                 return;
 164
 165         per_cpu(softlockup_print_ts, this_cpu) = touch_ts;
 166
 167         spin_lock(&print_lock);
 168         printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
 169                         this_cpu, now - touch_ts,
 170                         current->comm, task_pid_nr(current));
 171         print_modules();
 172         print_irqtrace_events(current);
 173         if (regs)
 174                 show_regs(regs);
 175         else
 176                 dump_stack();
 177         spin_unlock(&print_lock);
 178
 179         if (softlockup_panic)
 180                 panic("softlockup: hung tasks");
 181 }
 182
 183 /*
 184  * The watchdog thread - runs every second and touches the timestamp.
 185  */
 186 static int watchdog(void *__bind_cpu)
 187 {
 188         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 189
 190         sched_setscheduler(current, SCHED_FIFO, &param);
 191
 192         /* initialize timestamp */
 193         __touch_softlockup_watchdog();
 194
 195         set_current_state(TASK_INTERRUPTIBLE);
 196         /*
 197          * Run briefly once per second to reset the softlockup timestamp.
 198          * If this gets delayed for more than 60 seconds then the
 199          * debug-printout triggers in softlockup_tick().
 200          */
 201         while (!kthread_should_stop()) {
 202                 __touch_softlockup_watchdog();
 203                 schedule();
 204
 205                 if (kthread_should_stop())
 206                         break;
 207
 208                 set_current_state(TASK_INTERRUPTIBLE);
 209         }
 210         __set_current_state(TASK_RUNNING);
 211
 212         return 0;
 213 }
 214
 215 /*
 216  * Create/destroy watchdog threads as CPUs come and go:
 217  */
 218 static int __cpuinit
 219 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 220 {
 221         int hotcpu = (unsigned long)hcpu;
 222         struct task_struct *p;
 223
 224         switch (action) {
 225         case CPU_UP_PREPARE:
 226         case CPU_UP_PREPARE_FROZEN:
 227                 BUG_ON(per_cpu(softlockup_watchdog, hotcpu));
 228                 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
 229                 if (IS_ERR(p)) {
 230                         printk(KERN_ERR "watchdog for %i failed\n", hotcpu);
 231                         return NOTIFY_BAD;
 232                 }
 233                 per_cpu(softlockup_touch_ts, hotcpu) = 0;
 234                 per_cpu(softlockup_watchdog, hotcpu) = p;
 235                 kthread_bind(p, hotcpu);
 236                 break;
 237         case CPU_ONLINE:
 238         case CPU_ONLINE_FROZEN:
 239                 wake_up_process(per_cpu(softlockup_watchdog, hotcpu));
 240                 break;
 241 #ifdef CONFIG_HOTPLUG_CPU
 242         case CPU_UP_CANCELED:
 243         case CPU_UP_CANCELED_FROZEN:
 244                 if (!per_cpu(softlockup_watchdog, hotcpu))
 245                         break;
 246                 /* Unbind so it can run.  Fall thru. */
 247                 kthread_bind(per_cpu(softlockup_watchdog, hotcpu),
 248                              cpumask_any(cpu_online_mask));
 249         case CPU_DEAD:
 250         case CPU_DEAD_FROZEN:
 251                 p = per_cpu(softlockup_watchdog, hotcpu);
 252                 per_cpu(softlockup_watchdog, hotcpu) = NULL;
 253                 kthread_stop(p);
 254                 break;
 255 #endif /* CONFIG_HOTPLUG_CPU */
 256         }
 257         return NOTIFY_OK;
 258 }
 259
 260 static struct notifier_block __cpuinitdata cpu_nfb = {
 261         .notifier_call = cpu_callback
 262 };
 263
 264 static int __initdata nosoftlockup;
 265
 266 static int __init nosoftlockup_setup(char *str)
 267 {
 268         nosoftlockup = 1;
 269         return 1;
 270 }
 271 __setup("nosoftlockup", nosoftlockup_setup);
 272
 273 static int __init spawn_softlockup_task(void)
 274 {
 275         void *cpu = (void *)(long)smp_processor_id();
 276         int err;
 277
 278         if (nosoftlockup)
 279                 return 0;
 280
 281         err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 282         if (err == NOTIFY_BAD) {
 283                 BUG();
 284                 return 1;
 285         }
 286         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 287         register_cpu_notifier(&cpu_nfb);
 288
 289         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 290
 291         return 0;
 292 }
 293 early_initcall(spawn_softlockup_task);