FreeBSD/Linux Kernel Cross Reference
sys/kernel/hung_task.c

     /*
      * Detect Hung Task
      *
      * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
      *
      */
     
     #include <linux/mm.h>
     #include <linux/cpu.h>
    #include <linux/nmi.h>
    #include <linux/init.h>
    #include <linux/delay.h>
    #include <linux/freezer.h>
    #include <linux/kthread.h>
    #include <linux/lockdep.h>
    #include <linux/export.h>
    #include <linux/sysctl.h>
    
    /*
     * The number of tasks checked:
     */
    unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
    
    /*
     * Limit number of tasks checked in a batch.
     *
     * This value controls the preemptibility of khungtaskd since preemption
     * is disabled during the critical section. It also controls the size of
     * the RCU grace period. So it needs to be upper-bound.
     */
    #define HUNG_TASK_BATCHING 1024
    
    /*
     * Zero means infinite timeout - no checking done:
     */
    unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
    
    unsigned long __read_mostly sysctl_hung_task_warnings = 10;
    
    static int __read_mostly did_panic;
    
    static struct task_struct *watchdog_task;
    
    /*
     * Should we panic (and reboot, if panic_timeout= is set) when a
     * hung task is detected:
     */
    unsigned int __read_mostly sysctl_hung_task_panic =
                                    CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
    
    static int __init hung_task_panic_setup(char *str)
    {
            sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
    
            return 1;
    }
    __setup("hung_task_panic=", hung_task_panic_setup);
    
    static int
    hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
    {
            did_panic = 1;
    
            return NOTIFY_DONE;
    }
    
    static struct notifier_block panic_block = {
            .notifier_call = hung_task_panic,
    };
    
    static void check_hung_task(struct task_struct *t, unsigned long timeout)
    {
            unsigned long switch_count = t->nvcsw + t->nivcsw;
    
            /*
             * Ensure the task is not frozen.
             * Also, skip vfork and any other user process that freezer should skip.
             */
            if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
                return;
    
            /*
             * When a freshly created task is scheduled once, changes its state to
             * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
             * musn't be checked.
             */
            if (unlikely(!switch_count))
                    return;
    
            if (switch_count != t->last_switch_count) {
                    t->last_switch_count = switch_count;
                    return;
            }
            if (!sysctl_hung_task_warnings)
                    return;
            sysctl_hung_task_warnings--;
    
            /*
             * Ok, the task did not get scheduled for more than 2 minutes,
            * complain:
            */
           printk(KERN_ERR "INFO: task %s:%d blocked for more than "
                           "%ld seconds.\n", t->comm, t->pid, timeout);
           printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
                           " disables this message.\n");
           sched_show_task(t);
           debug_show_held_locks(t);
   
           touch_nmi_watchdog();
   
           if (sysctl_hung_task_panic) {
                   trigger_all_cpu_backtrace();
                   panic("hung_task: blocked tasks");
           }
   }
   
   /*
    * To avoid extending the RCU grace period for an unbounded amount of time,
    * periodically exit the critical section and enter a new one.
    *
    * For preemptible RCU it is sufficient to call rcu_read_unlock in order
    * to exit the grace period. For classic RCU, a reschedule is required.
    */
   static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
   {
           bool can_cont;
   
           get_task_struct(g);
           get_task_struct(t);
           rcu_read_unlock();
           cond_resched();
           rcu_read_lock();
           can_cont = pid_alive(g) && pid_alive(t);
           put_task_struct(t);
           put_task_struct(g);
   
           return can_cont;
   }
   
   /*
    * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
    * a really long time (120 seconds). If that happens, print out
    * a warning.
    */
   static void check_hung_uninterruptible_tasks(unsigned long timeout)
   {
           int max_count = sysctl_hung_task_check_count;
           int batch_count = HUNG_TASK_BATCHING;
           struct task_struct *g, *t;
   
           /*
            * If the system crashed already then all bets are off,
            * do not report extra hung tasks:
            */
           if (test_taint(TAINT_DIE) || did_panic)
                   return;
   
           rcu_read_lock();
           do_each_thread(g, t) {
                   if (!max_count--)
                           goto unlock;
                   if (!--batch_count) {
                           batch_count = HUNG_TASK_BATCHING;
                           if (!rcu_lock_break(g, t))
                                   goto unlock;
                   }
                   /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
                   if (t->state == TASK_UNINTERRUPTIBLE)
                           check_hung_task(t, timeout);
           } while_each_thread(g, t);
    unlock:
           rcu_read_unlock();
   }
   
   static unsigned long timeout_jiffies(unsigned long timeout)
   {
           /* timeout of 0 will disable the watchdog */
           return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
   }
   
   /*
    * Process updating of timeout sysctl
    */
   int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
                                     void __user *buffer,
                                     size_t *lenp, loff_t *ppos)
   {
           int ret;
   
           ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
   
           if (ret || !write)
                   goto out;
   
           wake_up_process(watchdog_task);
   
    out:
           return ret;
   }
   
   /*
    * kthread which checks for tasks stuck in D state
    */
   static int watchdog(void *dummy)
   {
           set_user_nice(current, 0);
   
           for ( ; ; ) {
                   unsigned long timeout = sysctl_hung_task_timeout_secs;
   
                   while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
                           timeout = sysctl_hung_task_timeout_secs;
   
                   check_hung_uninterruptible_tasks(timeout);
           }
   
           return 0;
   }
   
   static int __init hung_task_init(void)
   {
           atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
           watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
   
           return 0;
   }
   
   module_init(hung_task_init);

Cache object: b025d20ca3765ec506f85b4a1b6077a0