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