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/notifier.h>
  17 #include <linux/module.h>
  18
  19 #include <asm/irq_regs.h>
  20
  21 static DEFINE_SPINLOCK(print_lock);
  22
  23 static DEFINE_PER_CPU(unsigned long, touch_timestamp);
  24 static DEFINE_PER_CPU(unsigned long, print_timestamp);
  25 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
  26
  27 static int __read_mostly did_panic;
  28 int __read_mostly softlockup_thresh = 60;
  29
  30 /*
  31  * Should we panic (and reboot, if panic_timeout= is set) when a
  32  * soft-lockup occurs:
  33  */
  34 unsigned int __read_mostly softlockup_panic =
  35                                 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  36
  37 static int __init softlockup_panic_setup(char *str)
  38 {
  39         softlockup_panic = simple_strtoul(str, NULL, 0);
  40
  41         return 1;
  42 }
  43 __setup("softlockup_panic=", softlockup_panic_setup);
  44
  45 static int
  46 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
  47 {
  48         did_panic = 1;
  49
  50         return NOTIFY_DONE;
  51 }
  52
  53 static struct notifier_block panic_block = {
  54         .notifier_call = softlock_panic,
  55 };
  56
  57 /*
  58  * Returns seconds, approximately.  We don't need nanosecond
  59  * resolution, and we don't need to waste time with a big divide when
  60  * 2^30ns == 1.074s.
  61  */
  62 static unsigned long get_timestamp(int this_cpu)
  63 {
  64         return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
  65 }
  66
  67 static void __touch_softlockup_watchdog(void)
  68 {
  69         int this_cpu = raw_smp_processor_id();
  70
  71         __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
  72 }
  73
  74 void touch_softlockup_watchdog(void)
  75 {
  76         __raw_get_cpu_var(touch_timestamp) = 0;
  77 }
  78 EXPORT_SYMBOL(touch_softlockup_watchdog);
  79
  80 void touch_all_softlockup_watchdogs(void)
  81 {
  82         int cpu;
  83
  84         /* Cause each CPU to re-update its timestamp rather than complain */
  85         for_each_online_cpu(cpu)
  86                 per_cpu(touch_timestamp, cpu) = 0;
  87 }
  88 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
  89
  90 /*
  91  * This callback runs from the timer interrupt, and checks
  92  * whether the watchdog thread has hung or not:
  93  */
  94 void softlockup_tick(void)
  95 {
  96         int this_cpu = smp_processor_id();
  97         unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
  98         unsigned long print_timestamp;
  99         struct pt_regs *regs = get_irq_regs();
 100         unsigned long now;
 101
 102         /* Is detection switched off? */
 103         if (!per_cpu(watchdog_task, this_cpu) || softlockup_thresh <= 0) {
 104                 /* Be sure we don't false trigger if switched back on */
 105                 if (touch_timestamp)
 106                         per_cpu(touch_timestamp, this_cpu) = 0;
 107                 return;
 108         }
 109
 110         if (touch_timestamp == 0) {
 111                 __touch_softlockup_watchdog();
 112                 return;
 113         }
 114
 115         print_timestamp = per_cpu(print_timestamp, this_cpu);
 116
 117         /* report at most once a second */
 118         if ((print_timestamp >= touch_timestamp &&
 119                         print_timestamp < (touch_timestamp + 1)) ||
 120                         did_panic) {
 121                 return;
 122         }
 123
 124         /* do not print during early bootup: */
 125         if (unlikely(system_state != SYSTEM_RUNNING)) {
 126                 __touch_softlockup_watchdog();
 127                 return;
 128         }
 129
 130         now = get_timestamp(this_cpu);
 131
 132         /* Wake up the high-prio watchdog task every second: */
 133         if (now > (touch_timestamp + 1))
 134                 wake_up_process(per_cpu(watchdog_task, this_cpu));
 135
 136         /* Warn about unreasonable delays: */
 137         if (now <= (touch_timestamp + softlockup_thresh))
 138                 return;
 139
 140         per_cpu(print_timestamp, this_cpu) = touch_timestamp;
 141
 142         spin_lock(&print_lock);
 143         printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
 144                         this_cpu, now - touch_timestamp,
 145                         current->comm, task_pid_nr(current));
 146         if (regs)
 147                 show_regs(regs);
 148         else
 149                 dump_stack();
 150         spin_unlock(&print_lock);
 151
 152         if (softlockup_panic)
 153                 panic("softlockup: hung tasks");
 154 }
 155
 156 /*
 157  * Have a reasonable limit on the number of tasks checked:
 158  */
 159 unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
 160
 161 /*
 162  * Zero means infinite timeout - no checking done:
 163  */
 164 unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
 165
 166 unsigned long __read_mostly sysctl_hung_task_warnings = 10;
 167
 168 /*
 169  * Only do the hung-tasks check on one CPU:
 170  */
 171 static int check_cpu __read_mostly = -1;
 172
 173 static void check_hung_task(struct task_struct *t, unsigned long now)
 174 {
 175         unsigned long switch_count = t->nvcsw + t->nivcsw;
 176
 177         if (t->flags & PF_FROZEN)
 178                 return;
 179
 180         if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
 181                 t->last_switch_count = switch_count;
 182                 t->last_switch_timestamp = now;
 183                 return;
 184         }
 185         if ((long)(now - t->last_switch_timestamp) <
 186                                         sysctl_hung_task_timeout_secs)
 187                 return;
 188         if (sysctl_hung_task_warnings < 0)
 189                 return;
 190         sysctl_hung_task_warnings--;
 191
 192         /*
 193          * Ok, the task did not get scheduled for more than 2 minutes,
 194          * complain:
 195          */
 196         printk(KERN_ERR "INFO: task %s:%d blocked for more than "
 197                         "%ld seconds.\n", t->comm, t->pid,
 198                         sysctl_hung_task_timeout_secs);
 199         printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 200                         " disables this message.\n");
 201         sched_show_task(t);
 202         __debug_show_held_locks(t);
 203
 204         t->last_switch_timestamp = now;
 205         touch_nmi_watchdog();
 206
 207         if (softlockup_panic)
 208                 panic("softlockup: blocked tasks");
 209 }
 210
 211 /*
 212  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 213  * a really long time (120 seconds). If that happens, print out
 214  * a warning.
 215  */
 216 static void check_hung_uninterruptible_tasks(int this_cpu)
 217 {
 218         int max_count = sysctl_hung_task_check_count;
 219         unsigned long now = get_timestamp(this_cpu);
 220         struct task_struct *g, *t;
 221
 222         /*
 223          * If the system crashed already then all bets are off,
 224          * do not report extra hung tasks:
 225          */
 226         if ((tainted & TAINT_DIE) || did_panic)
 227                 return;
 228
 229         read_lock(&tasklist_lock);
 230         do_each_thread(g, t) {
 231                 if (!--max_count)
 232                         goto unlock;
 233                 if (t->state & TASK_UNINTERRUPTIBLE)
 234                         check_hung_task(t, now);
 235         } while_each_thread(g, t);
 236  unlock:
 237         read_unlock(&tasklist_lock);
 238 }
 239
 240 /*
 241  * The watchdog thread - runs every second and touches the timestamp.
 242  */
 243 static int watchdog(void *__bind_cpu)
 244 {
 245         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 246         int this_cpu = (long)__bind_cpu;
 247
 248         sched_setscheduler(current, SCHED_FIFO, &param);
 249
 250         /* initialize timestamp */
 251         __touch_softlockup_watchdog();
 252
 253         set_current_state(TASK_INTERRUPTIBLE);
 254         /*
 255          * Run briefly once per second to reset the softlockup timestamp.
 256          * If this gets delayed for more than 60 seconds then the
 257          * debug-printout triggers in softlockup_tick().
 258          */
 259         while (!kthread_should_stop()) {
 260                 __touch_softlockup_watchdog();
 261                 schedule();
 262
 263                 if (kthread_should_stop())
 264                         break;
 265
 266                 if (this_cpu == check_cpu) {
 267                         if (sysctl_hung_task_timeout_secs)
 268                                 check_hung_uninterruptible_tasks(this_cpu);
 269                 }
 270
 271                 set_current_state(TASK_INTERRUPTIBLE);
 272         }
 273         __set_current_state(TASK_RUNNING);
 274
 275         return 0;
 276 }
 277
 278 /*
 279  * Create/destroy watchdog threads as CPUs come and go:
 280  */
 281 static int __cpuinit
 282 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 283 {
 284         int hotcpu = (unsigned long)hcpu;
 285         struct task_struct *p;
 286
 287         switch (action) {
 288         case CPU_UP_PREPARE:
 289         case CPU_UP_PREPARE_FROZEN:
 290                 BUG_ON(per_cpu(watchdog_task, hotcpu));
 291                 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
 292                 if (IS_ERR(p)) {
 293                         printk(KERN_ERR "watchdog for %i failed\n", hotcpu);
 294                         return NOTIFY_BAD;
 295                 }
 296                 per_cpu(touch_timestamp, hotcpu) = 0;
 297                 per_cpu(watchdog_task, hotcpu) = p;
 298                 kthread_bind(p, hotcpu);
 299                 break;
 300         case CPU_ONLINE:
 301         case CPU_ONLINE_FROZEN:
 302                 check_cpu = any_online_cpu(cpu_online_map);
 303                 wake_up_process(per_cpu(watchdog_task, hotcpu));
 304                 break;
 305 #ifdef CONFIG_HOTPLUG_CPU
 306         case CPU_DOWN_PREPARE:
 307         case CPU_DOWN_PREPARE_FROZEN:
 308                 if (hotcpu == check_cpu) {
 309                         cpumask_t temp_cpu_online_map = cpu_online_map;
 310
 311                         cpu_clear(hotcpu, temp_cpu_online_map);
 312                         check_cpu = any_online_cpu(temp_cpu_online_map);
 313                 }
 314                 break;
 315
 316         case CPU_UP_CANCELED:
 317         case CPU_UP_CANCELED_FROZEN:
 318                 if (!per_cpu(watchdog_task, hotcpu))
 319                         break;
 320                 /* Unbind so it can run.  Fall thru. */
 321                 kthread_bind(per_cpu(watchdog_task, hotcpu),
 322                              any_online_cpu(cpu_online_map));
 323         case CPU_DEAD:
 324         case CPU_DEAD_FROZEN:
 325                 p = per_cpu(watchdog_task, hotcpu);
 326                 per_cpu(watchdog_task, hotcpu) = NULL;
 327                 kthread_stop(p);
 328                 break;
 329 #endif /* CONFIG_HOTPLUG_CPU */
 330         }
 331         return NOTIFY_OK;
 332 }
 333
 334 static struct notifier_block __cpuinitdata cpu_nfb = {
 335         .notifier_call = cpu_callback
 336 };
 337
 338 __init void spawn_softlockup_task(void)
 339 {
 340         void *cpu = (void *)(long)smp_processor_id();
 341         int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 342
 343         BUG_ON(err == NOTIFY_BAD);
 344         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 345         register_cpu_notifier(&cpu_nfb);
 346
 347         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 348 }