linux/kernel/softlockup.c
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   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
  20#include <asm/irq_regs.h>
  21
  22static DEFINE_SPINLOCK(print_lock);
  23
  24static DEFINE_PER_CPU(unsigned long, touch_timestamp);
  25static DEFINE_PER_CPU(unsigned long, print_timestamp);
  26static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
  27
  28static int __read_mostly did_panic;
  29int __read_mostly softlockup_thresh = 60;
  30
  31/*
  32 * Should we panic (and reboot, if panic_timeout= is set) when a
  33 * soft-lockup occurs:
  34 */
  35unsigned int __read_mostly softlockup_panic =
  36                                CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  37
  38static int __init softlockup_panic_setup(char *str)
  39{
  40        softlockup_panic = simple_strtoul(str, NULL, 0);
  41
  42        return 1;
  43}
  44__setup("softlockup_panic=", softlockup_panic_setup);
  45
  46static int
  47softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
  48{
  49        did_panic = 1;
  50
  51        return NOTIFY_DONE;
  52}
  53
  54static struct notifier_block panic_block = {
  55        .notifier_call = softlock_panic,
  56};
  57
  58/*
  59 * Returns seconds, approximately.  We don't need nanosecond
  60 * resolution, and we don't need to waste time with a big divide when
  61 * 2^30ns == 1.074s.
  62 */
  63static unsigned long get_timestamp(int this_cpu)
  64{
  65        return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
  66}
  67
  68static void __touch_softlockup_watchdog(void)
  69{
  70        int this_cpu = raw_smp_processor_id();
  71
  72        __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
  73}
  74
  75void touch_softlockup_watchdog(void)
  76{
  77        __raw_get_cpu_var(touch_timestamp) = 0;
  78}
  79EXPORT_SYMBOL(touch_softlockup_watchdog);
  80
  81void touch_all_softlockup_watchdogs(void)
  82{
  83        int cpu;
  84
  85        /* Cause each CPU to re-update its timestamp rather than complain */
  86        for_each_online_cpu(cpu)
  87                per_cpu(touch_timestamp, cpu) = 0;
  88}
  89EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
  90
  91/*
  92 * This callback runs from the timer interrupt, and checks
  93 * whether the watchdog thread has hung or not:
  94 */
  95void softlockup_tick(void)
  96{
  97        int this_cpu = smp_processor_id();
  98        unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
  99        unsigned long print_timestamp;
 100        struct pt_regs *regs = get_irq_regs();
 101        unsigned long now;
 102
 103        /* Is detection switched off? */
 104        if (!per_cpu(watchdog_task, this_cpu) || softlockup_thresh <= 0) {
 105                /* Be sure we don't false trigger if switched back on */
 106                if (touch_timestamp)
 107                        per_cpu(touch_timestamp, this_cpu) = 0;
 108                return;
 109        }
 110
 111        if (touch_timestamp == 0) {
 112                __touch_softlockup_watchdog();
 113                return;
 114        }
 115
 116        print_timestamp = per_cpu(print_timestamp, this_cpu);
 117
 118        /* report at most once a second */
 119        if (print_timestamp == touch_timestamp || did_panic)
 120                return;
 121
 122        /* do not print during early bootup: */
 123        if (unlikely(system_state != SYSTEM_RUNNING)) {
 124                __touch_softlockup_watchdog();
 125                return;
 126        }
 127
 128        now = get_timestamp(this_cpu);
 129
 130        /*
 131         * Wake up the high-prio watchdog task twice per
 132         * threshold timespan.
 133         */
 134        if (now > touch_timestamp + softlockup_thresh/2)
 135                wake_up_process(per_cpu(watchdog_task, this_cpu));
 136
 137        /* Warn about unreasonable delays: */
 138        if (now <= (touch_timestamp + softlockup_thresh))
 139                return;
 140
 141        per_cpu(print_timestamp, this_cpu) = touch_timestamp;
 142
 143        spin_lock(&print_lock);
 144        printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
 145                        this_cpu, now - touch_timestamp,
 146                        current->comm, task_pid_nr(current));
 147        print_modules();
 148        print_irqtrace_events(current);
 149        if (regs)
 150                show_regs(regs);
 151        else
 152                dump_stack();
 153        spin_unlock(&print_lock);
 154
 155        if (softlockup_panic)
 156                panic("softlockup: hung tasks");
 157}
 158
 159/*
 160 * Have a reasonable limit on the number of tasks checked:
 161 */
 162unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
 163
 164/*
 165 * Zero means infinite timeout - no checking done:
 166 */
 167unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
 168
 169unsigned long __read_mostly sysctl_hung_task_warnings = 10;
 170
 171/*
 172 * Only do the hung-tasks check on one CPU:
 173 */
 174static int check_cpu __read_mostly = -1;
 175
 176static void check_hung_task(struct task_struct *t, unsigned long now)
 177{
 178        unsigned long switch_count = t->nvcsw + t->nivcsw;
 179
 180        if (t->flags & PF_FROZEN)
 181                return;
 182
 183        if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
 184                t->last_switch_count = switch_count;
 185                t->last_switch_timestamp = now;
 186                return;
 187        }
 188        if ((long)(now - t->last_switch_timestamp) <
 189                                        sysctl_hung_task_timeout_secs)
 190                return;
 191        if (!sysctl_hung_task_warnings)
 192                return;
 193        sysctl_hung_task_warnings--;
 194
 195        /*
 196         * Ok, the task did not get scheduled for more than 2 minutes,
 197         * complain:
 198         */
 199        printk(KERN_ERR "INFO: task %s:%d blocked for more than "
 200                        "%ld seconds.\n", t->comm, t->pid,
 201                        sysctl_hung_task_timeout_secs);
 202        printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 203                        " disables this message.\n");
 204        sched_show_task(t);
 205        __debug_show_held_locks(t);
 206
 207        t->last_switch_timestamp = now;
 208        touch_nmi_watchdog();
 209
 210        if (softlockup_panic)
 211                panic("softlockup: blocked tasks");
 212}
 213
 214/*
 215 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 216 * a really long time (120 seconds). If that happens, print out
 217 * a warning.
 218 */
 219static void check_hung_uninterruptible_tasks(int this_cpu)
 220{
 221        int max_count = sysctl_hung_task_check_count;
 222        unsigned long now = get_timestamp(this_cpu);
 223        struct task_struct *g, *t;
 224
 225        /*
 226         * If the system crashed already then all bets are off,
 227         * do not report extra hung tasks:
 228         */
 229        if (test_taint(TAINT_DIE) || did_panic)
 230                return;
 231
 232        read_lock(&tasklist_lock);
 233        do_each_thread(g, t) {
 234                if (!--max_count)
 235                        goto unlock;
 236                /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 237                if (t->state == TASK_UNINTERRUPTIBLE)
 238                        check_hung_task(t, now);
 239        } while_each_thread(g, t);
 240 unlock:
 241        read_unlock(&tasklist_lock);
 242}
 243
 244/*
 245 * The watchdog thread - runs every second and touches the timestamp.
 246 */
 247static int watchdog(void *__bind_cpu)
 248{
 249        struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 250        int this_cpu = (long)__bind_cpu;
 251
 252        sched_setscheduler(current, SCHED_FIFO, &param);
 253
 254        /* initialize timestamp */
 255        __touch_softlockup_watchdog();
 256
 257        set_current_state(TASK_INTERRUPTIBLE);
 258        /*
 259         * Run briefly once per second to reset the softlockup timestamp.
 260         * If this gets delayed for more than 60 seconds then the
 261         * debug-printout triggers in softlockup_tick().
 262         */
 263        while (!kthread_should_stop()) {
 264                __touch_softlockup_watchdog();
 265                schedule();
 266
 267                if (kthread_should_stop())
 268                        break;
 269
 270                if (this_cpu == check_cpu) {
 271                        if (sysctl_hung_task_timeout_secs)
 272                                check_hung_uninterruptible_tasks(this_cpu);
 273                }
 274
 275                set_current_state(TASK_INTERRUPTIBLE);
 276        }
 277        __set_current_state(TASK_RUNNING);
 278
 279        return 0;
 280}
 281
 282/*
 283 * Create/destroy watchdog threads as CPUs come and go:
 284 */
 285static int __cpuinit
 286cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 287{
 288        int hotcpu = (unsigned long)hcpu;
 289        struct task_struct *p;
 290
 291        switch (action) {
 292        case CPU_UP_PREPARE:
 293        case CPU_UP_PREPARE_FROZEN:
 294                BUG_ON(per_cpu(watchdog_task, hotcpu));
 295                p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
 296                if (IS_ERR(p)) {
 297                        printk(KERN_ERR "watchdog for %i failed\n", hotcpu);
 298                        return NOTIFY_BAD;
 299                }
 300                per_cpu(touch_timestamp, hotcpu) = 0;
 301                per_cpu(watchdog_task, hotcpu) = p;
 302                kthread_bind(p, hotcpu);
 303                break;
 304        case CPU_ONLINE:
 305        case CPU_ONLINE_FROZEN:
 306                check_cpu = any_online_cpu(cpu_online_map);
 307                wake_up_process(per_cpu(watchdog_task, hotcpu));
 308                break;
 309#ifdef CONFIG_HOTPLUG_CPU
 310        case CPU_DOWN_PREPARE:
 311        case CPU_DOWN_PREPARE_FROZEN:
 312                if (hotcpu == check_cpu) {
 313                        cpumask_t temp_cpu_online_map = cpu_online_map;
 314
 315                        cpu_clear(hotcpu, temp_cpu_online_map);
 316                        check_cpu = any_online_cpu(temp_cpu_online_map);
 317                }
 318                break;
 319
 320        case CPU_UP_CANCELED:
 321        case CPU_UP_CANCELED_FROZEN:
 322                if (!per_cpu(watchdog_task, hotcpu))
 323                        break;
 324                /* Unbind so it can run.  Fall thru. */
 325                kthread_bind(per_cpu(watchdog_task, hotcpu),
 326                             any_online_cpu(cpu_online_map));
 327        case CPU_DEAD:
 328        case CPU_DEAD_FROZEN:
 329                p = per_cpu(watchdog_task, hotcpu);
 330                per_cpu(watchdog_task, hotcpu) = NULL;
 331                kthread_stop(p);
 332                break;
 333#endif /* CONFIG_HOTPLUG_CPU */
 334        }
 335        return NOTIFY_OK;
 336}
 337
 338static struct notifier_block __cpuinitdata cpu_nfb = {
 339        .notifier_call = cpu_callback
 340};
 341
 342static int __initdata nosoftlockup;
 343
 344static int __init nosoftlockup_setup(char *str)
 345{
 346        nosoftlockup = 1;
 347        return 1;
 348}
 349__setup("nosoftlockup", nosoftlockup_setup);
 350
 351static int __init spawn_softlockup_task(void)
 352{
 353        void *cpu = (void *)(long)smp_processor_id();
 354        int err;
 355
 356        if (nosoftlockup)
 357                return 0;
 358
 359        err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 360        if (err == NOTIFY_BAD) {
 361                BUG();
 362                return 1;
 363        }
 364        cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 365        register_cpu_notifier(&cpu_nfb);
 366
 367        atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 368
 369        return 0;
 370}
 371early_initcall(spawn_softlockup_task);
 372