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 #include <linux/utsname.h>
  19 #include <trace/events/sched.h>
  20
  21 /*
  22  * The number of tasks checked:
  23  */
  24 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  25
  26 /*
  27  * Limit number of tasks checked in a batch.
  28  *
  29  * This value controls the preemptibility of khungtaskd since preemption
  30  * is disabled during the critical section. It also controls the size of
  31  * the RCU grace period. So it needs to be upper-bound.
  32  */
  33 #define HUNG_TASK_BATCHING 1024
  34
  35 /*
  36  * Zero means infinite timeout - no checking done:
  37  */
  38 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  39
  40 int __read_mostly sysctl_hung_task_warnings = 10;
  41
  42 static int __read_mostly did_panic;
  43
  44 static struct task_struct *watchdog_task;
  45
  46 /*
  47  * Should we panic (and reboot, if panic_timeout= is set) when a
  48  * hung task is detected:
  49  */
  50 unsigned int __read_mostly sysctl_hung_task_panic =
  51                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  52
  53 static int __init hung_task_panic_setup(char *str)
  54 {
  55         sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
  56
  57         return 1;
  58 }
  59 __setup("hung_task_panic=", hung_task_panic_setup);
  60
  61 static int
  62 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  63 {
  64         did_panic = 1;
  65
  66         return NOTIFY_DONE;
  67 }
  68
  69 static struct notifier_block panic_block = {
  70         .notifier_call = hung_task_panic,
  71 };
  72
  73 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  74 {
  75         unsigned long switch_count = t->nvcsw + t->nivcsw;
  76
  77         /*
  78          * Ensure the task is not frozen.
  79          * Also, skip vfork and any other user process that freezer should skip.
  80          */
  81         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  82             return;
  83
  84         /*
  85          * When a freshly created task is scheduled once, changes its state to
  86          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
  87          * musn't be checked.
  88          */
  89         if (unlikely(!switch_count))
  90                 return;
  91
  92         if (switch_count != t->last_switch_count) {
  93                 t->last_switch_count = switch_count;
  94                 return;
  95         }
  96
  97         trace_sched_process_hang(t);
  98
  99         if (!sysctl_hung_task_warnings)
 100                 return;
 101
 102         if (sysctl_hung_task_warnings > 0)
 103                 sysctl_hung_task_warnings--;
 104
 105         /*
 106          * Ok, the task did not get scheduled for more than 2 minutes,
 107          * complain:
 108          */
 109         pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 110                 t->comm, t->pid, timeout);
 111         pr_err("      %s %s %.*s\n",
 112                 print_tainted(), init_utsname()->release,
 113                 (int)strcspn(init_utsname()->version, " "),
 114                 init_utsname()->version);
 115         pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 116                 " disables this message.\n");
 117         sched_show_task(t);
 118         debug_show_held_locks(t);
 119
 120         touch_nmi_watchdog();
 121
 122         if (sysctl_hung_task_panic) {
 123                 trigger_all_cpu_backtrace();
 124                 panic("hung_task: blocked tasks");
 125         }
 126 }
 127
 128 /*
 129  * To avoid extending the RCU grace period for an unbounded amount of time,
 130  * periodically exit the critical section and enter a new one.
 131  *
 132  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 133  * to exit the grace period. For classic RCU, a reschedule is required.
 134  */
 135 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 136 {
 137         bool can_cont;
 138
 139         get_task_struct(g);
 140         get_task_struct(t);
 141         rcu_read_unlock();
 142         cond_resched();
 143         rcu_read_lock();
 144         can_cont = pid_alive(g) && pid_alive(t);
 145         put_task_struct(t);
 146         put_task_struct(g);
 147
 148         return can_cont;
 149 }
 150
 151 /*
 152  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 153  * a really long time (120 seconds). If that happens, print out
 154  * a warning.
 155  */
 156 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 157 {
 158         int max_count = sysctl_hung_task_check_count;
 159         int batch_count = HUNG_TASK_BATCHING;
 160         struct task_struct *g, *t;
 161
 162         /*
 163          * If the system crashed already then all bets are off,
 164          * do not report extra hung tasks:
 165          */
 166         if (test_taint(TAINT_DIE) || did_panic)
 167                 return;
 168
 169         rcu_read_lock();
 170         do_each_thread(g, t) {
 171                 if (!max_count--)
 172                         goto unlock;
 173                 if (!--batch_count) {
 174                         batch_count = HUNG_TASK_BATCHING;
 175                         if (!rcu_lock_break(g, t))
 176                                 goto unlock;
 177                 }
 178                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 179                 if (t->state == TASK_UNINTERRUPTIBLE)
 180                         check_hung_task(t, timeout);
 181         } while_each_thread(g, t);
 182  unlock:
 183         rcu_read_unlock();
 184 }
 185
 186 static unsigned long timeout_jiffies(unsigned long timeout)
 187 {
 188         /* timeout of 0 will disable the watchdog */
 189         return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
 190 }
 191
 192 /*
 193  * Process updating of timeout sysctl
 194  */
 195 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 196                                   void __user *buffer,
 197                                   size_t *lenp, loff_t *ppos)
 198 {
 199         int ret;
 200
 201         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 202
 203         if (ret || !write)
 204                 goto out;
 205
 206         wake_up_process(watchdog_task);
 207
 208  out:
 209         return ret;
 210 }
 211
 212 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 213
 214 void reset_hung_task_detector(void)
 215 {
 216         atomic_set(&reset_hung_task, 1);
 217 }
 218 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 219
 220 /*
 221  * kthread which checks for tasks stuck in D state
 222  */
 223 static int watchdog(void *dummy)
 224 {
 225         set_user_nice(current, 0);
 226
 227         for ( ; ; ) {
 228                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 229
 230                 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
 231                         timeout = sysctl_hung_task_timeout_secs;
 232
 233                 if (atomic_xchg(&reset_hung_task, 0))
 234                         continue;
 235
 236                 check_hung_uninterruptible_tasks(timeout);
 237         }
 238
 239         return 0;
 240 }
 241
 242 static int __init hung_task_init(void)
 243 {
 244         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 245         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 246
 247         return 0;
 248 }
 249
 250 module_init(hung_task_init);