kernel/hung_task.c

   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/module.h>
  17 #include <linux/sysctl.h>
  18
  19 /*
  20  * The number of tasks checked:
  21  */
  22 unsigned 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  */
  36 unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
  37
  38 unsigned long __read_mostly sysctl_hung_task_warnings = 10;
  39
  40 static int __read_mostly did_panic;
  41
  42 static 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  */
  48 unsigned int __read_mostly sysctl_hung_task_panic =
  49                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  50
  51 static 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
  59 static int
  60 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  61 {
  62         did_panic = 1;
  63
  64         return NOTIFY_DONE;
  65 }
  66
  67 static struct notifier_block panic_block = {
  68         .notifier_call = hung_task_panic,
  69 };
  70
  71 static 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, when a freshly created task is scheduled once, changes
  78          * its state to TASK_UNINTERRUPTIBLE without having ever been
  79          * switched out once, it musn't be checked.
  80          */
  81         if (unlikely(t->flags & PF_FROZEN || !switch_count))
  82                 return;
  83
  84         if (switch_count != t->last_switch_count) {
  85                 t->last_switch_count = switch_count;
  86                 return;
  87         }
  88         if (!sysctl_hung_task_warnings)
  89                 return;
  90         sysctl_hung_task_warnings--;
  91
  92         /*
  93          * Ok, the task did not get scheduled for more than 2 minutes,
  94          * complain:
  95          */
  96         printk(KERN_ERR "INFO: task %s:%d blocked for more than "
  97                         "%ld seconds.\n", t->comm, t->pid, timeout);
  98         printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
  99                         " disables this message.\n");
 100         sched_show_task(t);
 101         debug_show_held_locks(t);
 102
 103         touch_nmi_watchdog();
 104
 105         if (sysctl_hung_task_panic)
 106                 panic("hung_task: blocked tasks");
 107 }
 108
 109 /*
 110  * To avoid extending the RCU grace period for an unbounded amount of time,
 111  * periodically exit the critical section and enter a new one.
 112  *
 113  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 114  * to exit the grace period. For classic RCU, a reschedule is required.
 115  */
 116 static void rcu_lock_break(struct task_struct *g, struct task_struct *t)
 117 {
 118         get_task_struct(g);
 119         get_task_struct(t);
 120         rcu_read_unlock();
 121         cond_resched();
 122         rcu_read_lock();
 123         put_task_struct(t);
 124         put_task_struct(g);
 125 }
 126
 127 /*
 128  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 129  * a really long time (120 seconds). If that happens, print out
 130  * a warning.
 131  */
 132 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 133 {
 134         int max_count = sysctl_hung_task_check_count;
 135         int batch_count = HUNG_TASK_BATCHING;
 136         struct task_struct *g, *t;
 137
 138         /*
 139          * If the system crashed already then all bets are off,
 140          * do not report extra hung tasks:
 141          */
 142         if (test_taint(TAINT_DIE) || did_panic)
 143                 return;
 144
 145         rcu_read_lock();
 146         do_each_thread(g, t) {
 147                 if (!max_count--)
 148                         goto unlock;
 149                 if (!--batch_count) {
 150                         batch_count = HUNG_TASK_BATCHING;
 151                         rcu_lock_break(g, t);
 152                         /* Exit if t or g was unhashed during refresh. */
 153                         if (t->state == TASK_DEAD || g->state == TASK_DEAD)
 154                                 goto unlock;
 155                 }
 156                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 157                 if (t->state == TASK_UNINTERRUPTIBLE)
 158                         check_hung_task(t, timeout);
 159         } while_each_thread(g, t);
 160  unlock:
 161         rcu_read_unlock();
 162 }
 163
 164 static unsigned long timeout_jiffies(unsigned long timeout)
 165 {
 166         /* timeout of 0 will disable the watchdog */
 167         return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
 168 }
 169
 170 /*
 171  * Process updating of timeout sysctl
 172  */
 173 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 174                                   void __user *buffer,
 175                                   size_t *lenp, loff_t *ppos)
 176 {
 177         int ret;
 178
 179         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 180
 181         if (ret || !write)
 182                 goto out;
 183
 184         wake_up_process(watchdog_task);
 185
 186  out:
 187         return ret;
 188 }
 189
 190 /*
 191  * kthread which checks for tasks stuck in D state
 192  */
 193 static int watchdog(void *dummy)
 194 {
 195         set_user_nice(current, 0);
 196
 197         for ( ; ; ) {
 198                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 199
 200                 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
 201                         timeout = sysctl_hung_task_timeout_secs;
 202
 203                 check_hung_uninterruptible_tasks(timeout);
 204         }
 205
 206         return 0;
 207 }
 208
 209 static int __init hung_task_init(void)
 210 {
 211         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 212         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 213
 214         return 0;
 215 }
 216
 217 module_init(hung_task_init);