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         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  56
  57         if (rc)
  58                 return rc;
  59         return 1;
  60 }
  61 __setup("hung_task_panic=", hung_task_panic_setup);
  62
  63 static int
  64 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  65 {
  66         did_panic = 1;
  67
  68         return NOTIFY_DONE;
  69 }
  70
  71 static struct notifier_block panic_block = {
  72         .notifier_call = hung_task_panic,
  73 };
  74
  75 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  76 {
  77         unsigned long switch_count = t->nvcsw + t->nivcsw;
  78
  79         /*
  80          * Ensure the task is not frozen.
  81          * Also, skip vfork and any other user process that freezer should skip.
  82          */
  83         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  84             return;
  85
  86         /*
  87          * When a freshly created task is scheduled once, changes its state to
  88          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
  89          * musn't be checked.
  90          */
  91         if (unlikely(!switch_count))
  92                 return;
  93
  94         if (switch_count != t->last_switch_count) {
  95                 t->last_switch_count = switch_count;
  96                 return;
  97         }
  98
  99         trace_sched_process_hang(t);
 100
 101         if (!sysctl_hung_task_warnings)
 102                 return;
 103
 104         if (sysctl_hung_task_warnings > 0)
 105                 sysctl_hung_task_warnings--;
 106
 107         /*
 108          * Ok, the task did not get scheduled for more than 2 minutes,
 109          * complain:
 110          */
 111         pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 112                 t->comm, t->pid, timeout);
 113         pr_err("      %s %s %.*s\n",
 114                 print_tainted(), init_utsname()->release,
 115                 (int)strcspn(init_utsname()->version, " "),
 116                 init_utsname()->version);
 117         pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 118                 " disables this message.\n");
 119         sched_show_task(t);
 120         debug_show_held_locks(t);
 121
 122         touch_nmi_watchdog();
 123
 124         if (sysctl_hung_task_panic) {
 125                 trigger_all_cpu_backtrace();
 126                 panic("hung_task: blocked tasks");
 127         }
 128 }
 129
 130 /*
 131  * To avoid extending the RCU grace period for an unbounded amount of time,
 132  * periodically exit the critical section and enter a new one.
 133  *
 134  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 135  * to exit the grace period. For classic RCU, a reschedule is required.
 136  */
 137 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 138 {
 139         bool can_cont;
 140
 141         get_task_struct(g);
 142         get_task_struct(t);
 143         rcu_read_unlock();
 144         cond_resched();
 145         rcu_read_lock();
 146         can_cont = pid_alive(g) && pid_alive(t);
 147         put_task_struct(t);
 148         put_task_struct(g);
 149
 150         return can_cont;
 151 }
 152
 153 /*
 154  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 155  * a really long time (120 seconds). If that happens, print out
 156  * a warning.
 157  */
 158 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 159 {
 160         int max_count = sysctl_hung_task_check_count;
 161         int batch_count = HUNG_TASK_BATCHING;
 162         struct task_struct *g, *t;
 163
 164         /*
 165          * If the system crashed already then all bets are off,
 166          * do not report extra hung tasks:
 167          */
 168         if (test_taint(TAINT_DIE) || did_panic)
 169                 return;
 170
 171         rcu_read_lock();
 172         for_each_process_thread(g, t) {
 173                 if (!max_count--)
 174                         goto unlock;
 175                 if (!--batch_count) {
 176                         batch_count = HUNG_TASK_BATCHING;
 177                         if (!rcu_lock_break(g, t))
 178                                 goto unlock;
 179                 }
 180                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 181                 if (t->state == TASK_UNINTERRUPTIBLE)
 182                         check_hung_task(t, timeout);
 183         }
 184  unlock:
 185         rcu_read_unlock();
 186 }
 187
 188 static long hung_timeout_jiffies(unsigned long last_checked,
 189                                  unsigned long timeout)
 190 {
 191         /* timeout of 0 will disable the watchdog */
 192         return timeout ? last_checked - jiffies + timeout * HZ :
 193                 MAX_SCHEDULE_TIMEOUT;
 194 }
 195
 196 /*
 197  * Process updating of timeout sysctl
 198  */
 199 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 200                                   void __user *buffer,
 201                                   size_t *lenp, loff_t *ppos)
 202 {
 203         int ret;
 204
 205         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 206
 207         if (ret || !write)
 208                 goto out;
 209
 210         wake_up_process(watchdog_task);
 211
 212  out:
 213         return ret;
 214 }
 215
 216 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 217
 218 void reset_hung_task_detector(void)
 219 {
 220         atomic_set(&reset_hung_task, 1);
 221 }
 222 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 223
 224 /*
 225  * kthread which checks for tasks stuck in D state
 226  */
 227 static int watchdog(void *dummy)
 228 {
 229         unsigned long hung_last_checked = jiffies;
 230
 231         set_user_nice(current, 0);
 232
 233         for ( ; ; ) {
 234                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 235                 long t = hung_timeout_jiffies(hung_last_checked, timeout);
 236
 237                 if (t <= 0) {
 238                         if (!atomic_xchg(&reset_hung_task, 0))
 239                                 check_hung_uninterruptible_tasks(timeout);
 240                         hung_last_checked = jiffies;
 241                         continue;
 242                 }
 243                 schedule_timeout_interruptible(t);
 244         }
 245
 246         return 0;
 247 }
 248
 249 static int __init hung_task_init(void)
 250 {
 251         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 252         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 253
 254         return 0;
 255 }
 256 subsys_initcall(hung_task_init);