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 static unsigned long __read_mostly hung_task_poll_jiffies;
  38
  39 unsigned long __read_mostly sysctl_hung_task_warnings = 10;
  40
  41 static int __read_mostly did_panic;
  42
  43 static 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  */
  49 unsigned int __read_mostly sysctl_hung_task_panic =
  50                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  51
  52 static 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
  60 static int
  61 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  62 {
  63         did_panic = 1;
  64
  65         return NOTIFY_DONE;
  66 }
  67
  68 static struct notifier_block panic_block = {
  69         .notifier_call = hung_task_panic,
  70 };
  71
  72 /*
  73  * Returns seconds, approximately.  We don't need nanosecond
  74  * resolution, and we don't need to waste time with a big divide when
  75  * 2^30ns == 1.074s.
  76  */
  77 static unsigned long get_timestamp(void)
  78 {
  79         int this_cpu = raw_smp_processor_id();
  80
  81         return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
  82 }
  83
  84 static void check_hung_task(struct task_struct *t, unsigned long now,
  85                             unsigned long timeout)
  86 {
  87         unsigned long switch_count = t->nvcsw + t->nivcsw;
  88
  89         if (t->flags & PF_FROZEN)
  90                 return;
  91
  92         if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
  93                 t->last_switch_count = switch_count;
  94                 t->last_switch_timestamp = now;
  95                 return;
  96         }
  97         if ((long)(now - t->last_switch_timestamp) < timeout)
  98                 return;
  99         if (!sysctl_hung_task_warnings)
 100                 return;
 101         sysctl_hung_task_warnings--;
 102
 103         /*
 104          * Ok, the task did not get scheduled for more than 2 minutes,
 105          * complain:
 106          */
 107         printk(KERN_ERR "INFO: task %s:%d blocked for more than "
 108                         "%ld seconds.\n", t->comm, t->pid, timeout);
 109         printk(KERN_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         t->last_switch_timestamp = now;
 115         touch_nmi_watchdog();
 116
 117         if (sysctl_hung_task_panic)
 118                 panic("hung_task: blocked tasks");
 119 }
 120
 121 /*
 122  * To avoid extending the RCU grace period for an unbounded amount of time,
 123  * periodically exit the critical section and enter a new one.
 124  *
 125  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 126  * exit the grace period. For classic RCU, a reschedule is required.
 127  */
 128 static void rcu_lock_break(struct task_struct *g, struct task_struct *t)
 129 {
 130         get_task_struct(g);
 131         get_task_struct(t);
 132         rcu_read_unlock();
 133         cond_resched();
 134         rcu_read_lock();
 135         put_task_struct(t);
 136         put_task_struct(g);
 137 }
 138
 139 /*
 140  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 141  * a really long time (120 seconds). If that happens, print out
 142  * a warning.
 143  */
 144 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 145 {
 146         int max_count = sysctl_hung_task_check_count;
 147         int batch_count = HUNG_TASK_BATCHING;
 148         unsigned long now = get_timestamp();
 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         read_lock(&tasklist_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                         rcu_lock_break(g, t);
 165                         /* Exit if t or g was unhashed during refresh. */
 166                         if (t->state == TASK_DEAD || g->state == TASK_DEAD)
 167                                 goto unlock;
 168                 }
 169                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 170                 if (t->state == TASK_UNINTERRUPTIBLE)
 171                         check_hung_task(t, now, timeout);
 172         } while_each_thread(g, t);
 173  unlock:
 174         read_unlock(&tasklist_lock);
 175 }
 176
 177 static void update_poll_jiffies(void)
 178 {
 179         /* timeout of 0 will disable the watchdog */
 180         if (sysctl_hung_task_timeout_secs == 0)
 181                 hung_task_poll_jiffies = MAX_SCHEDULE_TIMEOUT;
 182         else
 183                 hung_task_poll_jiffies = sysctl_hung_task_timeout_secs * HZ / 2;
 184 }
 185
 186 /*
 187  * Process updating of timeout sysctl
 188  */
 189 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 190                                   struct file *filp, void __user *buffer,
 191                                   size_t *lenp, loff_t *ppos)
 192 {
 193         int ret;
 194
 195         ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
 196
 197         if (ret || !write)
 198                 goto out;
 199
 200         update_poll_jiffies();
 201
 202         wake_up_process(watchdog_task);
 203
 204  out:
 205         return ret;
 206 }
 207
 208 /*
 209  * kthread which checks for tasks stuck in D state
 210  */
 211 static int watchdog(void *dummy)
 212 {
 213         set_user_nice(current, 0);
 214         update_poll_jiffies();
 215
 216         for ( ; ; ) {
 217                 unsigned long timeout;
 218
 219                 while (schedule_timeout_interruptible(hung_task_poll_jiffies));
 220
 221                 /*
 222                  * Need to cache timeout here to avoid timeout being set
 223                  * to 0 via sysctl while inside check_hung_*_tasks().
 224                  */
 225                 timeout = sysctl_hung_task_timeout_secs;
 226                 if (timeout)
 227                         check_hung_uninterruptible_tasks(timeout);
 228         }
 229
 230         return 0;
 231 }
 232
 233 static int __init hung_task_init(void)
 234 {
 235         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 236         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 237
 238         return 0;
 239 }
 240
 241 module_init(hung_task_init);