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