linux/kernel/hung_task.c
<<
>>
Prefs
   1/*
   2 * Detect Hung Task
   3 *
   4 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
   5 *
   6 */
   7
   8#include <linux/mm.h>
   9#include <linux/cpu.h>
  10#include <linux/nmi.h>
  11#include <linux/init.h>
  12#include <linux/delay.h>
  13#include <linux/freezer.h>
  14#include <linux/kthread.h>
  15#include <linux/lockdep.h>
  16#include <linux/export.h>
  17#include <linux/sysctl.h>
  18#include <linux/suspend.h>
  19#include <linux/utsname.h>
  20#include <linux/sched/signal.h>
  21#include <linux/sched/debug.h>
  22
  23#include <trace/events/sched.h>
  24
  25/*
  26 * The number of tasks checked:
  27 */
  28int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  29
  30/*
  31 * Limit number of tasks checked in a batch.
  32 *
  33 * This value controls the preemptibility of khungtaskd since preemption
  34 * is disabled during the critical section. It also controls the size of
  35 * the RCU grace period. So it needs to be upper-bound.
  36 */
  37#define HUNG_TASK_BATCHING 1024
  38
  39/*
  40 * Zero means infinite timeout - no checking done:
  41 */
  42unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  43
  44/*
  45 * Zero (default value) means use sysctl_hung_task_timeout_secs:
  46 */
  47unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
  48
  49int __read_mostly sysctl_hung_task_warnings = 10;
  50
  51static int __read_mostly did_panic;
  52static bool hung_task_show_lock;
  53static bool hung_task_call_panic;
  54
  55static struct task_struct *watchdog_task;
  56
  57/*
  58 * Should we panic (and reboot, if panic_timeout= is set) when a
  59 * hung task is detected:
  60 */
  61unsigned int __read_mostly sysctl_hung_task_panic =
  62                                CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  63
  64static int __init hung_task_panic_setup(char *str)
  65{
  66        int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  67
  68        if (rc)
  69                return rc;
  70        return 1;
  71}
  72__setup("hung_task_panic=", hung_task_panic_setup);
  73
  74static int
  75hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  76{
  77        did_panic = 1;
  78
  79        return NOTIFY_DONE;
  80}
  81
  82static struct notifier_block panic_block = {
  83        .notifier_call = hung_task_panic,
  84};
  85
  86static void check_hung_task(struct task_struct *t, unsigned long timeout)
  87{
  88        unsigned long switch_count = t->nvcsw + t->nivcsw;
  89
  90        /*
  91         * Ensure the task is not frozen.
  92         * Also, skip vfork and any other user process that freezer should skip.
  93         */
  94        if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  95            return;
  96
  97        /*
  98         * When a freshly created task is scheduled once, changes its state to
  99         * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
 100         * musn't be checked.
 101         */
 102        if (unlikely(!switch_count))
 103                return;
 104
 105        if (switch_count != t->last_switch_count) {
 106                t->last_switch_count = switch_count;
 107                t->last_switch_time = jiffies;
 108                return;
 109        }
 110        if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
 111                return;
 112
 113        trace_sched_process_hang(t);
 114
 115        if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
 116                return;
 117
 118        /*
 119         * Ok, the task did not get scheduled for more than 2 minutes,
 120         * complain:
 121         */
 122        if (sysctl_hung_task_warnings) {
 123                if (sysctl_hung_task_warnings > 0)
 124                        sysctl_hung_task_warnings--;
 125                pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 126                        t->comm, t->pid, timeout);
 127                pr_err("      %s %s %.*s\n",
 128                        print_tainted(), init_utsname()->release,
 129                        (int)strcspn(init_utsname()->version, " "),
 130                        init_utsname()->version);
 131                pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 132                        " disables this message.\n");
 133                sched_show_task(t);
 134                hung_task_show_lock = true;
 135        }
 136
 137        touch_nmi_watchdog();
 138
 139        if (sysctl_hung_task_panic) {
 140                hung_task_show_lock = true;
 141                hung_task_call_panic = true;
 142        }
 143}
 144
 145/*
 146 * To avoid extending the RCU grace period for an unbounded amount of time,
 147 * periodically exit the critical section and enter a new one.
 148 *
 149 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 150 * to exit the grace period. For classic RCU, a reschedule is required.
 151 */
 152static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 153{
 154        bool can_cont;
 155
 156        get_task_struct(g);
 157        get_task_struct(t);
 158        rcu_read_unlock();
 159        cond_resched();
 160        rcu_read_lock();
 161        can_cont = pid_alive(g) && pid_alive(t);
 162        put_task_struct(t);
 163        put_task_struct(g);
 164
 165        return can_cont;
 166}
 167
 168/*
 169 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 170 * a really long time (120 seconds). If that happens, print out
 171 * a warning.
 172 */
 173static void check_hung_uninterruptible_tasks(unsigned long timeout)
 174{
 175        int max_count = sysctl_hung_task_check_count;
 176        int batch_count = HUNG_TASK_BATCHING;
 177        struct task_struct *g, *t;
 178
 179        /*
 180         * If the system crashed already then all bets are off,
 181         * do not report extra hung tasks:
 182         */
 183        if (test_taint(TAINT_DIE) || did_panic)
 184                return;
 185
 186        hung_task_show_lock = false;
 187        rcu_read_lock();
 188        for_each_process_thread(g, t) {
 189                if (!max_count--)
 190                        goto unlock;
 191                if (!--batch_count) {
 192                        batch_count = HUNG_TASK_BATCHING;
 193                        if (!rcu_lock_break(g, t))
 194                                goto unlock;
 195                }
 196                /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 197                if (t->state == TASK_UNINTERRUPTIBLE)
 198                        check_hung_task(t, timeout);
 199        }
 200 unlock:
 201        rcu_read_unlock();
 202        if (hung_task_show_lock)
 203                debug_show_all_locks();
 204        if (hung_task_call_panic) {
 205                trigger_all_cpu_backtrace();
 206                panic("hung_task: blocked tasks");
 207        }
 208}
 209
 210static long hung_timeout_jiffies(unsigned long last_checked,
 211                                 unsigned long timeout)
 212{
 213        /* timeout of 0 will disable the watchdog */
 214        return timeout ? last_checked - jiffies + timeout * HZ :
 215                MAX_SCHEDULE_TIMEOUT;
 216}
 217
 218/*
 219 * Process updating of timeout sysctl
 220 */
 221int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 222                                  void __user *buffer,
 223                                  size_t *lenp, loff_t *ppos)
 224{
 225        int ret;
 226
 227        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 228
 229        if (ret || !write)
 230                goto out;
 231
 232        wake_up_process(watchdog_task);
 233
 234 out:
 235        return ret;
 236}
 237
 238static atomic_t reset_hung_task = ATOMIC_INIT(0);
 239
 240void reset_hung_task_detector(void)
 241{
 242        atomic_set(&reset_hung_task, 1);
 243}
 244EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 245
 246static bool hung_detector_suspended;
 247
 248static int hungtask_pm_notify(struct notifier_block *self,
 249                              unsigned long action, void *hcpu)
 250{
 251        switch (action) {
 252        case PM_SUSPEND_PREPARE:
 253        case PM_HIBERNATION_PREPARE:
 254        case PM_RESTORE_PREPARE:
 255                hung_detector_suspended = true;
 256                break;
 257        case PM_POST_SUSPEND:
 258        case PM_POST_HIBERNATION:
 259        case PM_POST_RESTORE:
 260                hung_detector_suspended = false;
 261                break;
 262        default:
 263                break;
 264        }
 265        return NOTIFY_OK;
 266}
 267
 268/*
 269 * kthread which checks for tasks stuck in D state
 270 */
 271static int watchdog(void *dummy)
 272{
 273        unsigned long hung_last_checked = jiffies;
 274
 275        set_user_nice(current, 0);
 276
 277        for ( ; ; ) {
 278                unsigned long timeout = sysctl_hung_task_timeout_secs;
 279                unsigned long interval = sysctl_hung_task_check_interval_secs;
 280                long t;
 281
 282                if (interval == 0)
 283                        interval = timeout;
 284                interval = min_t(unsigned long, interval, timeout);
 285                t = hung_timeout_jiffies(hung_last_checked, interval);
 286                if (t <= 0) {
 287                        if (!atomic_xchg(&reset_hung_task, 0) &&
 288                            !hung_detector_suspended)
 289                                check_hung_uninterruptible_tasks(timeout);
 290                        hung_last_checked = jiffies;
 291                        continue;
 292                }
 293                schedule_timeout_interruptible(t);
 294        }
 295
 296        return 0;
 297}
 298
 299static int __init hung_task_init(void)
 300{
 301        atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 302
 303        /* Disable hung task detector on suspend */
 304        pm_notifier(hungtask_pm_notify, 0);
 305
 306        watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 307
 308        return 0;
 309}
 310subsys_initcall(hung_task_init);
 311