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/suspend.h>
  19 #include <linux/utsname.h>
  20 #include <linux/sched/signal.h>
  21 #include <linux/sched/debug.h>
  22
  23 #include <trace/events/sched.h>
  24
  25 /*
  26  * The number of tasks checked:
  27  */
  28 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  29
  30 /*
  31  * Limit number of tasks checked in a batch.
  32  *
  33  * This value controls the preemptibility of khungtaskd since preemption
  34  * is disabled during the critical section. It also controls the size of
  35  * the RCU grace period. So it needs to be upper-bound.
  36  */
  37 #define HUNG_TASK_BATCHING 1024
  38
  39 /*
  40  * Zero means infinite timeout - no checking done:
  41  */
  42 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  43
  44 /*
  45  * Zero (default value) means use sysctl_hung_task_timeout_secs:
  46  */
  47 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
  48
  49 int __read_mostly sysctl_hung_task_warnings = 10;
  50
  51 static int __read_mostly did_panic;
  52 static bool hung_task_show_lock;
  53 static bool hung_task_call_panic;
  54
  55 static struct task_struct *watchdog_task;
  56
  57 /*
  58  * Should we panic (and reboot, if panic_timeout= is set) when a
  59  * hung task is detected:
  60  */
  61 unsigned int __read_mostly sysctl_hung_task_panic =
  62                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  63
  64 static int __init hung_task_panic_setup(char *str)
  65 {
  66         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  67
  68         if (rc)
  69                 return rc;
  70         return 1;
  71 }
  72 __setup("hung_task_panic=", hung_task_panic_setup);
  73
  74 static int
  75 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  76 {
  77         did_panic = 1;
  78
  79         return NOTIFY_DONE;
  80 }
  81
  82 static struct notifier_block panic_block = {
  83         .notifier_call = hung_task_panic,
  84 };
  85
  86 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  87 {
  88         unsigned long switch_count = t->nvcsw + t->nivcsw;
  89
  90         /*
  91          * Ensure the task is not frozen.
  92          * Also, skip vfork and any other user process that freezer should skip.
  93          */
  94         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  95             return;
  96
  97         /*
  98          * When a freshly created task is scheduled once, changes its state to
  99          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
 100          * musn't be checked.
 101          */
 102         if (unlikely(!switch_count))
 103                 return;
 104
 105         if (switch_count != t->last_switch_count) {
 106                 t->last_switch_count = switch_count;
 107                 t->last_switch_time = jiffies;
 108                 return;
 109         }
 110         if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
 111                 return;
 112
 113         trace_sched_process_hang(t);
 114
 115         if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
 116                 return;
 117
 118         /*
 119          * Ok, the task did not get scheduled for more than 2 minutes,
 120          * complain:
 121          */
 122         if (sysctl_hung_task_warnings) {
 123                 if (sysctl_hung_task_warnings > 0)
 124                         sysctl_hung_task_warnings--;
 125                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 126                         t->comm, t->pid, timeout);
 127                 pr_err("      %s %s %.*s\n",
 128                         print_tainted(), init_utsname()->release,
 129                         (int)strcspn(init_utsname()->version, " "),
 130                         init_utsname()->version);
 131                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 132                         " disables this message.\n");
 133                 sched_show_task(t);
 134                 hung_task_show_lock = true;
 135         }
 136
 137         touch_nmi_watchdog();
 138
 139         if (sysctl_hung_task_panic) {
 140                 hung_task_show_lock = true;
 141                 hung_task_call_panic = true;
 142         }
 143 }
 144
 145 /*
 146  * To avoid extending the RCU grace period for an unbounded amount of time,
 147  * periodically exit the critical section and enter a new one.
 148  *
 149  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 150  * to exit the grace period. For classic RCU, a reschedule is required.
 151  */
 152 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 153 {
 154         bool can_cont;
 155
 156         get_task_struct(g);
 157         get_task_struct(t);
 158         rcu_read_unlock();
 159         cond_resched();
 160         rcu_read_lock();
 161         can_cont = pid_alive(g) && pid_alive(t);
 162         put_task_struct(t);
 163         put_task_struct(g);
 164
 165         return can_cont;
 166 }
 167
 168 /*
 169  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 170  * a really long time (120 seconds). If that happens, print out
 171  * a warning.
 172  */
 173 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 174 {
 175         int max_count = sysctl_hung_task_check_count;
 176         int batch_count = HUNG_TASK_BATCHING;
 177         struct task_struct *g, *t;
 178
 179         /*
 180          * If the system crashed already then all bets are off,
 181          * do not report extra hung tasks:
 182          */
 183         if (test_taint(TAINT_DIE) || did_panic)
 184                 return;
 185
 186         hung_task_show_lock = false;
 187         rcu_read_lock();
 188         for_each_process_thread(g, t) {
 189                 if (!max_count--)
 190                         goto unlock;
 191                 if (!--batch_count) {
 192                         batch_count = HUNG_TASK_BATCHING;
 193                         if (!rcu_lock_break(g, t))
 194                                 goto unlock;
 195                 }
 196                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 197                 if (t->state == TASK_UNINTERRUPTIBLE)
 198                         check_hung_task(t, timeout);
 199         }
 200  unlock:
 201         rcu_read_unlock();
 202         if (hung_task_show_lock)
 203                 debug_show_all_locks();
 204         if (hung_task_call_panic) {
 205                 trigger_all_cpu_backtrace();
 206                 panic("hung_task: blocked tasks");
 207         }
 208 }
 209
 210 static long hung_timeout_jiffies(unsigned long last_checked,
 211                                  unsigned long timeout)
 212 {
 213         /* timeout of 0 will disable the watchdog */
 214         return timeout ? last_checked - jiffies + timeout * HZ :
 215                 MAX_SCHEDULE_TIMEOUT;
 216 }
 217
 218 /*
 219  * Process updating of timeout sysctl
 220  */
 221 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 222                                   void __user *buffer,
 223                                   size_t *lenp, loff_t *ppos)
 224 {
 225         int ret;
 226
 227         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 228
 229         if (ret || !write)
 230                 goto out;
 231
 232         wake_up_process(watchdog_task);
 233
 234  out:
 235         return ret;
 236 }
 237
 238 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 239
 240 void reset_hung_task_detector(void)
 241 {
 242         atomic_set(&reset_hung_task, 1);
 243 }
 244 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 245
 246 static bool hung_detector_suspended;
 247
 248 static int hungtask_pm_notify(struct notifier_block *self,
 249                               unsigned long action, void *hcpu)
 250 {
 251         switch (action) {
 252         case PM_SUSPEND_PREPARE:
 253         case PM_HIBERNATION_PREPARE:
 254         case PM_RESTORE_PREPARE:
 255                 hung_detector_suspended = true;
 256                 break;
 257         case PM_POST_SUSPEND:
 258         case PM_POST_HIBERNATION:
 259         case PM_POST_RESTORE:
 260                 hung_detector_suspended = false;
 261                 break;
 262         default:
 263                 break;
 264         }
 265         return NOTIFY_OK;
 266 }
 267
 268 /*
 269  * kthread which checks for tasks stuck in D state
 270  */
 271 static int watchdog(void *dummy)
 272 {
 273         unsigned long hung_last_checked = jiffies;
 274
 275         set_user_nice(current, 0);
 276
 277         for ( ; ; ) {
 278                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 279                 unsigned long interval = sysctl_hung_task_check_interval_secs;
 280                 long t;
 281
 282                 if (interval == 0)
 283                         interval = timeout;
 284                 interval = min_t(unsigned long, interval, timeout);
 285                 t = hung_timeout_jiffies(hung_last_checked, interval);
 286                 if (t <= 0) {
 287                         if (!atomic_xchg(&reset_hung_task, 0) &&
 288                             !hung_detector_suspended)
 289                                 check_hung_uninterruptible_tasks(timeout);
 290                         hung_last_checked = jiffies;
 291                         continue;
 292                 }
 293                 schedule_timeout_interruptible(t);
 294         }
 295
 296         return 0;
 297 }
 298
 299 static int __init hung_task_init(void)
 300 {
 301         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 302
 303         /* Disable hung task detector on suspend */
 304         pm_notifier(hungtask_pm_notify, 0);
 305
 306         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 307
 308         return 0;
 309 }
 310 subsys_initcall(hung_task_init);