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/export.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 = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  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, 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                 panic("hung_task: blocked tasks");
 113 }
 114
 115 /*
 116  * To avoid extending the RCU grace period for an unbounded amount of time,
 117  * periodically exit the critical section and enter a new one.
 118  *
 119  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 120  * to exit the grace period. For classic RCU, a reschedule is required.
 121  */
 122 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 123 {
 124         bool can_cont;
 125
 126         get_task_struct(g);
 127         get_task_struct(t);
 128         rcu_read_unlock();
 129         cond_resched();
 130         rcu_read_lock();
 131         can_cont = pid_alive(g) && pid_alive(t);
 132         put_task_struct(t);
 133         put_task_struct(g);
 134
 135         return can_cont;
 136 }
 137
 138 /*
 139  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 140  * a really long time (120 seconds). If that happens, print out
 141  * a warning.
 142  */
 143 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 144 {
 145         int max_count = sysctl_hung_task_check_count;
 146         int batch_count = HUNG_TASK_BATCHING;
 147         struct task_struct *g, *t;
 148
 149         /*
 150          * If the system crashed already then all bets are off,
 151          * do not report extra hung tasks:
 152          */
 153         if (test_taint(TAINT_DIE) || did_panic)
 154                 return;
 155
 156         rcu_read_lock();
 157         do_each_thread(g, t) {
 158                 if (!max_count--)
 159                         goto unlock;
 160                 if (!--batch_count) {
 161                         batch_count = HUNG_TASK_BATCHING;
 162                         if (!rcu_lock_break(g, t))
 163                                 goto unlock;
 164                 }
 165                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 166                 if (t->state == TASK_UNINTERRUPTIBLE)
 167                         check_hung_task(t, timeout);
 168         } while_each_thread(g, t);
 169  unlock:
 170         rcu_read_unlock();
 171 }
 172
 173 static unsigned long timeout_jiffies(unsigned long timeout)
 174 {
 175         /* timeout of 0 will disable the watchdog */
 176         return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
 177 }
 178
 179 /*
 180  * Process updating of timeout sysctl
 181  */
 182 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 183                                   void __user *buffer,
 184                                   size_t *lenp, loff_t *ppos)
 185 {
 186         int ret;
 187
 188         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 189
 190         if (ret || !write)
 191                 goto out;
 192
 193         wake_up_process(watchdog_task);
 194
 195  out:
 196         return ret;
 197 }
 198
 199 /*
 200  * kthread which checks for tasks stuck in D state
 201  */
 202 static int watchdog(void *dummy)
 203 {
 204         set_user_nice(current, 0);
 205
 206         for ( ; ; ) {
 207                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 208
 209                 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
 210                         timeout = sysctl_hung_task_timeout_secs;
 211
 212                 check_hung_uninterruptible_tasks(timeout);
 213         }
 214
 215         return 0;
 216 }
 217
 218 static int __init hung_task_init(void)
 219 {
 220         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 221         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 222
 223         return 0;
 224 }
 225
 226 module_init(hung_task_init);