linux/kernel/hung_task.c
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   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/utsname.h>
  19
  20/*
  21 * The number of tasks checked:
  22 */
  23unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  24
  25/*
  26 * Limit number of tasks checked in a batch.
  27 *
  28 * This value controls the preemptibility of khungtaskd since preemption
  29 * is disabled during the critical section. It also controls the size of
  30 * the RCU grace period. So it needs to be upper-bound.
  31 */
  32#define HUNG_TASK_BATCHING 1024
  33
  34/*
  35 * Zero means infinite timeout - no checking done:
  36 */
  37unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  38
  39unsigned long __read_mostly sysctl_hung_task_warnings = 10;
  40
  41static int __read_mostly did_panic;
  42
  43static struct task_struct *watchdog_task;
  44
  45/*
  46 * Should we panic (and reboot, if panic_timeout= is set) when a
  47 * hung task is detected:
  48 */
  49unsigned int __read_mostly sysctl_hung_task_panic =
  50                                CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  51
  52static int __init hung_task_panic_setup(char *str)
  53{
  54        sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
  55
  56        return 1;
  57}
  58__setup("hung_task_panic=", hung_task_panic_setup);
  59
  60static int
  61hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  62{
  63        did_panic = 1;
  64
  65        return NOTIFY_DONE;
  66}
  67
  68static struct notifier_block panic_block = {
  69        .notifier_call = hung_task_panic,
  70};
  71
  72static void check_hung_task(struct task_struct *t, unsigned long timeout)
  73{
  74        unsigned long switch_count = t->nvcsw + t->nivcsw;
  75
  76        /*
  77         * Ensure the task is not frozen.
  78         * Also, skip vfork and any other user process that freezer should skip.
  79         */
  80        if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  81            return;
  82
  83        /*
  84         * When a freshly created task is scheduled once, changes its state to
  85         * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
  86         * musn't be checked.
  87         */
  88        if (unlikely(!switch_count))
  89                return;
  90
  91        if (switch_count != t->last_switch_count) {
  92                t->last_switch_count = switch_count;
  93                return;
  94        }
  95        if (!sysctl_hung_task_warnings)
  96                return;
  97        sysctl_hung_task_warnings--;
  98
  99        /*
 100         * Ok, the task did not get scheduled for more than 2 minutes,
 101         * complain:
 102         */
 103        pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 104                t->comm, t->pid, timeout);
 105        pr_err("      %s %s %.*s\n",
 106                print_tainted(), init_utsname()->release,
 107                (int)strcspn(init_utsname()->version, " "),
 108                init_utsname()->version);
 109        pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 110                " disables this message.\n");
 111        sched_show_task(t);
 112        debug_show_held_locks(t);
 113
 114        touch_nmi_watchdog();
 115
 116        if (sysctl_hung_task_panic) {
 117                trigger_all_cpu_backtrace();
 118                panic("hung_task: blocked tasks");
 119        }
 120}
 121
 122/*
 123 * To avoid extending the RCU grace period for an unbounded amount of time,
 124 * periodically exit the critical section and enter a new one.
 125 *
 126 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 127 * to exit the grace period. For classic RCU, a reschedule is required.
 128 */
 129static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 130{
 131        bool can_cont;
 132
 133        get_task_struct(g);
 134        get_task_struct(t);
 135        rcu_read_unlock();
 136        cond_resched();
 137        rcu_read_lock();
 138        can_cont = pid_alive(g) && pid_alive(t);
 139        put_task_struct(t);
 140        put_task_struct(g);
 141
 142        return can_cont;
 143}
 144
 145/*
 146 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 147 * a really long time (120 seconds). If that happens, print out
 148 * a warning.
 149 */
 150static void check_hung_uninterruptible_tasks(unsigned long timeout)
 151{
 152        int max_count = sysctl_hung_task_check_count;
 153        int batch_count = HUNG_TASK_BATCHING;
 154        struct task_struct *g, *t;
 155
 156        /*
 157         * If the system crashed already then all bets are off,
 158         * do not report extra hung tasks:
 159         */
 160        if (test_taint(TAINT_DIE) || did_panic)
 161                return;
 162
 163        rcu_read_lock();
 164        do_each_thread(g, t) {
 165                if (!max_count--)
 166                        goto unlock;
 167                if (!--batch_count) {
 168                        batch_count = HUNG_TASK_BATCHING;
 169                        if (!rcu_lock_break(g, t))
 170                                goto unlock;
 171                }
 172                /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 173                if (t->state == TASK_UNINTERRUPTIBLE)
 174                        check_hung_task(t, timeout);
 175        } while_each_thread(g, t);
 176 unlock:
 177        rcu_read_unlock();
 178}
 179
 180static unsigned long timeout_jiffies(unsigned long timeout)
 181{
 182        /* timeout of 0 will disable the watchdog */
 183        return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
 184}
 185
 186/*
 187 * Process updating of timeout sysctl
 188 */
 189int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 190                                  void __user *buffer,
 191                                  size_t *lenp, loff_t *ppos)
 192{
 193        int ret;
 194
 195        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 196
 197        if (ret || !write)
 198                goto out;
 199
 200        wake_up_process(watchdog_task);
 201
 202 out:
 203        return ret;
 204}
 205
 206/*
 207 * kthread which checks for tasks stuck in D state
 208 */
 209static int watchdog(void *dummy)
 210{
 211        set_user_nice(current, 0);
 212
 213        for ( ; ; ) {
 214                unsigned long timeout = sysctl_hung_task_timeout_secs;
 215
 216                while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
 217                        timeout = sysctl_hung_task_timeout_secs;
 218
 219                check_hung_uninterruptible_tasks(timeout);
 220        }
 221
 222        return 0;
 223}
 224
 225static int __init hung_task_init(void)
 226{
 227        atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 228        watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 229
 230        return 0;
 231}
 232
 233module_init(hung_task_init);
 234
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