kernel/hung_task.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Detect Hung Task
   4  *
   5  * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
   6  *
   7  */
   8
   9 #include <linux/mm.h>
  10 #include <linux/cpu.h>
  11 #include <linux/nmi.h>
  12 #include <linux/init.h>
  13 #include <linux/delay.h>
  14 #include <linux/freezer.h>
  15 #include <linux/kthread.h>
  16 #include <linux/lockdep.h>
  17 #include <linux/export.h>
  18 #include <linux/panic_notifier.h>
  19 #include <linux/sysctl.h>
  20 #include <linux/suspend.h>
  21 #include <linux/utsname.h>
  22 #include <linux/sched/signal.h>
  23 #include <linux/sched/debug.h>
  24 #include <linux/sched/sysctl.h>
  25
  26 #include <trace/events/sched.h>
  27
  28 /*
  29  * The number of tasks checked:
  30  */
  31 static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  32
  33 /*
  34  * Limit number of tasks checked in a batch.
  35  *
  36  * This value controls the preemptibility of khungtaskd since preemption
  37  * is disabled during the critical section. It also controls the size of
  38  * the RCU grace period. So it needs to be upper-bound.
  39  */
  40 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
  41
  42 /*
  43  * Zero means infinite timeout - no checking done:
  44  */
  45 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  46 EXPORT_SYMBOL_GPL(sysctl_hung_task_timeout_secs);
  47
  48 /*
  49  * Zero (default value) means use sysctl_hung_task_timeout_secs:
  50  */
  51 static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
  52
  53 static int __read_mostly sysctl_hung_task_warnings = 10;
  54
  55 static int __read_mostly did_panic;
  56 static bool hung_task_show_lock;
  57 static bool hung_task_call_panic;
  58 static bool hung_task_show_all_bt;
  59
  60 static struct task_struct *watchdog_task;
  61
  62 #ifdef CONFIG_SMP
  63 /*
  64  * Should we dump all CPUs backtraces in a hung task event?
  65  * Defaults to 0, can be changed via sysctl.
  66  */
  67 static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
  68 #else
  69 #define sysctl_hung_task_all_cpu_backtrace 0
  70 #endif /* CONFIG_SMP */
  71
  72 /*
  73  * Should we panic (and reboot, if panic_timeout= is set) when a
  74  * hung task is detected:
  75  */
  76 static unsigned int __read_mostly sysctl_hung_task_panic =
  77         IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
  78
  79 static int
  80 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  81 {
  82         did_panic = 1;
  83
  84         return NOTIFY_DONE;
  85 }
  86
  87 static struct notifier_block panic_block = {
  88         .notifier_call = hung_task_panic,
  89 };
  90
  91 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  92 {
  93         unsigned long switch_count = t->nvcsw + t->nivcsw;
  94
  95         /*
  96          * Ensure the task is not frozen.
  97          * Also, skip vfork and any other user process that freezer should skip.
  98          */
  99         if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN))
 100                 return;
 101
 102         /*
 103          * When a freshly created task is scheduled once, changes its state to
 104          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
 105          * musn't be checked.
 106          */
 107         if (unlikely(!switch_count))
 108                 return;
 109
 110         if (switch_count != t->last_switch_count) {
 111                 t->last_switch_count = switch_count;
 112                 t->last_switch_time = jiffies;
 113                 return;
 114         }
 115         if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
 116                 return;
 117
 118         trace_sched_process_hang(t);
 119
 120         if (sysctl_hung_task_panic) {
 121                 console_verbose();
 122                 hung_task_show_lock = true;
 123                 hung_task_call_panic = true;
 124         }
 125
 126         /*
 127          * Ok, the task did not get scheduled for more than 2 minutes,
 128          * complain:
 129          */
 130         if (sysctl_hung_task_warnings) {
 131                 if (sysctl_hung_task_warnings > 0)
 132                         sysctl_hung_task_warnings--;
 133                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 134                        t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
 135                 pr_err("      %s %s %.*s\n",
 136                         print_tainted(), init_utsname()->release,
 137                         (int)strcspn(init_utsname()->version, " "),
 138                         init_utsname()->version);
 139                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 140                         " disables this message.\n");
 141                 sched_show_task(t);
 142                 hung_task_show_lock = true;
 143
 144                 if (sysctl_hung_task_all_cpu_backtrace)
 145                         hung_task_show_all_bt = true;
 146                 if (!sysctl_hung_task_warnings)
 147                         pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
 148         }
 149
 150         touch_nmi_watchdog();
 151 }
 152
 153 /*
 154  * To avoid extending the RCU grace period for an unbounded amount of time,
 155  * periodically exit the critical section and enter a new one.
 156  *
 157  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 158  * to exit the grace period. For classic RCU, a reschedule is required.
 159  */
 160 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 161 {
 162         bool can_cont;
 163
 164         get_task_struct(g);
 165         get_task_struct(t);
 166         rcu_read_unlock();
 167         cond_resched();
 168         rcu_read_lock();
 169         can_cont = pid_alive(g) && pid_alive(t);
 170         put_task_struct(t);
 171         put_task_struct(g);
 172
 173         return can_cont;
 174 }
 175
 176 /*
 177  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 178  * a really long time (120 seconds). If that happens, print out
 179  * a warning.
 180  */
 181 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 182 {
 183         int max_count = sysctl_hung_task_check_count;
 184         unsigned long last_break = jiffies;
 185         struct task_struct *g, *t;
 186
 187         /*
 188          * If the system crashed already then all bets are off,
 189          * do not report extra hung tasks:
 190          */
 191         if (test_taint(TAINT_DIE) || did_panic)
 192                 return;
 193
 194         hung_task_show_lock = false;
 195         rcu_read_lock();
 196         for_each_process_thread(g, t) {
 197                 unsigned int state;
 198
 199                 if (!max_count--)
 200                         goto unlock;
 201                 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
 202                         if (!rcu_lock_break(g, t))
 203                                 goto unlock;
 204                         last_break = jiffies;
 205                 }
 206                 /*
 207                  * skip the TASK_KILLABLE tasks -- these can be killed
 208                  * skip the TASK_IDLE tasks -- those are genuinely idle
 209                  */
 210                 state = READ_ONCE(t->__state);
 211                 if ((state & TASK_UNINTERRUPTIBLE) &&
 212                     !(state & TASK_WAKEKILL) &&
 213                     !(state & TASK_NOLOAD))
 214                         check_hung_task(t, timeout);
 215         }
 216  unlock:
 217         rcu_read_unlock();
 218         if (hung_task_show_lock)
 219                 debug_show_all_locks();
 220
 221         if (hung_task_show_all_bt) {
 222                 hung_task_show_all_bt = false;
 223                 trigger_all_cpu_backtrace();
 224         }
 225
 226         if (hung_task_call_panic)
 227                 panic("hung_task: blocked tasks");
 228 }
 229
 230 static long hung_timeout_jiffies(unsigned long last_checked,
 231                                  unsigned long timeout)
 232 {
 233         /* timeout of 0 will disable the watchdog */
 234         return timeout ? last_checked - jiffies + timeout * HZ :
 235                 MAX_SCHEDULE_TIMEOUT;
 236 }
 237
 238 #ifdef CONFIG_SYSCTL
 239 /*
 240  * Process updating of timeout sysctl
 241  */
 242 static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 243                                   void *buffer,
 244                                   size_t *lenp, loff_t *ppos)
 245 {
 246         int ret;
 247
 248         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 249
 250         if (ret || !write)
 251                 goto out;
 252
 253         wake_up_process(watchdog_task);
 254
 255  out:
 256         return ret;
 257 }
 258
 259 /*
 260  * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
 261  * and hung_task_check_interval_secs
 262  */
 263 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
 264 static struct ctl_table hung_task_sysctls[] = {
 265 #ifdef CONFIG_SMP
 266         {
 267                 .procname       = "hung_task_all_cpu_backtrace",
 268                 .data           = &sysctl_hung_task_all_cpu_backtrace,
 269                 .maxlen         = sizeof(int),
 270                 .mode           = 0644,
 271                 .proc_handler   = proc_dointvec_minmax,
 272                 .extra1         = SYSCTL_ZERO,
 273                 .extra2         = SYSCTL_ONE,
 274         },
 275 #endif /* CONFIG_SMP */
 276         {
 277                 .procname       = "hung_task_panic",
 278                 .data           = &sysctl_hung_task_panic,
 279                 .maxlen         = sizeof(int),
 280                 .mode           = 0644,
 281                 .proc_handler   = proc_dointvec_minmax,
 282                 .extra1         = SYSCTL_ZERO,
 283                 .extra2         = SYSCTL_ONE,
 284         },
 285         {
 286                 .procname       = "hung_task_check_count",
 287                 .data           = &sysctl_hung_task_check_count,
 288                 .maxlen         = sizeof(int),
 289                 .mode           = 0644,
 290                 .proc_handler   = proc_dointvec_minmax,
 291                 .extra1         = SYSCTL_ZERO,
 292         },
 293         {
 294                 .procname       = "hung_task_timeout_secs",
 295                 .data           = &sysctl_hung_task_timeout_secs,
 296                 .maxlen         = sizeof(unsigned long),
 297                 .mode           = 0644,
 298                 .proc_handler   = proc_dohung_task_timeout_secs,
 299                 .extra2         = (void *)&hung_task_timeout_max,
 300         },
 301         {
 302                 .procname       = "hung_task_check_interval_secs",
 303                 .data           = &sysctl_hung_task_check_interval_secs,
 304                 .maxlen         = sizeof(unsigned long),
 305                 .mode           = 0644,
 306                 .proc_handler   = proc_dohung_task_timeout_secs,
 307                 .extra2         = (void *)&hung_task_timeout_max,
 308         },
 309         {
 310                 .procname       = "hung_task_warnings",
 311                 .data           = &sysctl_hung_task_warnings,
 312                 .maxlen         = sizeof(int),
 313                 .mode           = 0644,
 314                 .proc_handler   = proc_dointvec_minmax,
 315                 .extra1         = SYSCTL_NEG_ONE,
 316         },
 317         {}
 318 };
 319
 320 static void __init hung_task_sysctl_init(void)
 321 {
 322         register_sysctl_init("kernel", hung_task_sysctls);
 323 }
 324 #else
 325 #define hung_task_sysctl_init() do { } while (0)
 326 #endif /* CONFIG_SYSCTL */
 327
 328
 329 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 330
 331 void reset_hung_task_detector(void)
 332 {
 333         atomic_set(&reset_hung_task, 1);
 334 }
 335 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 336
 337 static bool hung_detector_suspended;
 338
 339 static int hungtask_pm_notify(struct notifier_block *self,
 340                               unsigned long action, void *hcpu)
 341 {
 342         switch (action) {
 343         case PM_SUSPEND_PREPARE:
 344         case PM_HIBERNATION_PREPARE:
 345         case PM_RESTORE_PREPARE:
 346                 hung_detector_suspended = true;
 347                 break;
 348         case PM_POST_SUSPEND:
 349         case PM_POST_HIBERNATION:
 350         case PM_POST_RESTORE:
 351                 hung_detector_suspended = false;
 352                 break;
 353         default:
 354                 break;
 355         }
 356         return NOTIFY_OK;
 357 }
 358
 359 /*
 360  * kthread which checks for tasks stuck in D state
 361  */
 362 static int watchdog(void *dummy)
 363 {
 364         unsigned long hung_last_checked = jiffies;
 365
 366         set_user_nice(current, 0);
 367
 368         for ( ; ; ) {
 369                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 370                 unsigned long interval = sysctl_hung_task_check_interval_secs;
 371                 long t;
 372
 373                 if (interval == 0)
 374                         interval = timeout;
 375                 interval = min_t(unsigned long, interval, timeout);
 376                 t = hung_timeout_jiffies(hung_last_checked, interval);
 377                 if (t <= 0) {
 378                         if (!atomic_xchg(&reset_hung_task, 0) &&
 379                             !hung_detector_suspended)
 380                                 check_hung_uninterruptible_tasks(timeout);
 381                         hung_last_checked = jiffies;
 382                         continue;
 383                 }
 384                 schedule_timeout_interruptible(t);
 385         }
 386
 387         return 0;
 388 }
 389
 390 static int __init hung_task_init(void)
 391 {
 392         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 393
 394         /* Disable hung task detector on suspend */
 395         pm_notifier(hungtask_pm_notify, 0);
 396
 397         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 398         hung_task_sysctl_init();
 399
 400         return 0;
 401 }
 402 subsys_initcall(hung_task_init);