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