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
  47 /*
  48  * Zero (default value) means use sysctl_hung_task_timeout_secs:
  49  */
  50 static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
  51
  52 static 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 static 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(READ_ONCE(t->__state) & TASK_FROZEN))
  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                 if (sysctl_hung_task_warnings > 0)
 131                         sysctl_hung_task_warnings--;
 132                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 133                        t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
 134                 pr_err("      %s %s %.*s\n",
 135                         print_tainted(), init_utsname()->release,
 136                         (int)strcspn(init_utsname()->version, " "),
 137                         init_utsname()->version);
 138                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 139                         " disables this message.\n");
 140                 sched_show_task(t);
 141                 hung_task_show_lock = true;
 142
 143                 if (sysctl_hung_task_all_cpu_backtrace)
 144                         hung_task_show_all_bt = true;
 145                 if (!sysctl_hung_task_warnings)
 146                         pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
 147         }
 148
 149         touch_nmi_watchdog();
 150 }
 151
 152 /*
 153  * To avoid extending the RCU grace period for an unbounded amount of time,
 154  * periodically exit the critical section and enter a new one.
 155  *
 156  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 157  * to exit the grace period. For classic RCU, a reschedule is required.
 158  */
 159 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 160 {
 161         bool can_cont;
 162
 163         get_task_struct(g);
 164         get_task_struct(t);
 165         rcu_read_unlock();
 166         cond_resched();
 167         rcu_read_lock();
 168         can_cont = pid_alive(g) && pid_alive(t);
 169         put_task_struct(t);
 170         put_task_struct(g);
 171
 172         return can_cont;
 173 }
 174
 175 /*
 176  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 177  * a really long time (120 seconds). If that happens, print out
 178  * a warning.
 179  */
 180 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 181 {
 182         int max_count = sysctl_hung_task_check_count;
 183         unsigned long last_break = jiffies;
 184         struct task_struct *g, *t;
 185
 186         /*
 187          * If the system crashed already then all bets are off,
 188          * do not report extra hung tasks:
 189          */
 190         if (test_taint(TAINT_DIE) || did_panic)
 191                 return;
 192
 193         hung_task_show_lock = false;
 194         rcu_read_lock();
 195         for_each_process_thread(g, t) {
 196                 unsigned int state;
 197
 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                 /*
 206                  * skip the TASK_KILLABLE tasks -- these can be killed
 207                  * skip the TASK_IDLE tasks -- those are genuinely idle
 208                  */
 209                 state = READ_ONCE(t->__state);
 210                 if ((state & TASK_UNINTERRUPTIBLE) &&
 211                     !(state & TASK_WAKEKILL) &&
 212                     !(state & TASK_NOLOAD))
 213                         check_hung_task(t, timeout);
 214         }
 215  unlock:
 216         rcu_read_unlock();
 217         if (hung_task_show_lock)
 218                 debug_show_all_locks();
 219
 220         if (hung_task_show_all_bt) {
 221                 hung_task_show_all_bt = false;
 222                 trigger_all_cpu_backtrace();
 223         }
 224
 225         if (hung_task_call_panic)
 226                 panic("hung_task: blocked tasks");
 227 }
 228
 229 static long hung_timeout_jiffies(unsigned long last_checked,
 230                                  unsigned long timeout)
 231 {
 232         /* timeout of 0 will disable the watchdog */
 233         return timeout ? last_checked - jiffies + timeout * HZ :
 234                 MAX_SCHEDULE_TIMEOUT;
 235 }
 236
 237 #ifdef CONFIG_SYSCTL
 238 /*
 239  * Process updating of timeout sysctl
 240  */
 241 static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 242                                   void *buffer,
 243                                   size_t *lenp, loff_t *ppos)
 244 {
 245         int ret;
 246
 247         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 248
 249         if (ret || !write)
 250                 goto out;
 251
 252         wake_up_process(watchdog_task);
 253
 254  out:
 255         return ret;
 256 }
 257
 258 /*
 259  * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
 260  * and hung_task_check_interval_secs
 261  */
 262 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
 263 static struct ctl_table hung_task_sysctls[] = {
 264 #ifdef CONFIG_SMP
 265         {
 266                 .procname       = "hung_task_all_cpu_backtrace",
 267                 .data           = &sysctl_hung_task_all_cpu_backtrace,
 268                 .maxlen         = sizeof(int),
 269                 .mode           = 0644,
 270                 .proc_handler   = proc_dointvec_minmax,
 271                 .extra1         = SYSCTL_ZERO,
 272                 .extra2         = SYSCTL_ONE,
 273         },
 274 #endif /* CONFIG_SMP */
 275         {
 276                 .procname       = "hung_task_panic",
 277                 .data           = &sysctl_hung_task_panic,
 278                 .maxlen         = sizeof(int),
 279                 .mode           = 0644,
 280                 .proc_handler   = proc_dointvec_minmax,
 281                 .extra1         = SYSCTL_ZERO,
 282                 .extra2         = SYSCTL_ONE,
 283         },
 284         {
 285                 .procname       = "hung_task_check_count",
 286                 .data           = &sysctl_hung_task_check_count,
 287                 .maxlen         = sizeof(int),
 288                 .mode           = 0644,
 289                 .proc_handler   = proc_dointvec_minmax,
 290                 .extra1         = SYSCTL_ZERO,
 291         },
 292         {
 293                 .procname       = "hung_task_timeout_secs",
 294                 .data           = &sysctl_hung_task_timeout_secs,
 295                 .maxlen         = sizeof(unsigned long),
 296                 .mode           = 0644,
 297                 .proc_handler   = proc_dohung_task_timeout_secs,
 298                 .extra2         = (void *)&hung_task_timeout_max,
 299         },
 300         {
 301                 .procname       = "hung_task_check_interval_secs",
 302                 .data           = &sysctl_hung_task_check_interval_secs,
 303                 .maxlen         = sizeof(unsigned long),
 304                 .mode           = 0644,
 305                 .proc_handler   = proc_dohung_task_timeout_secs,
 306                 .extra2         = (void *)&hung_task_timeout_max,
 307         },
 308         {
 309                 .procname       = "hung_task_warnings",
 310                 .data           = &sysctl_hung_task_warnings,
 311                 .maxlen         = sizeof(int),
 312                 .mode           = 0644,
 313                 .proc_handler   = proc_dointvec_minmax,
 314                 .extra1         = SYSCTL_NEG_ONE,
 315         },
 316         {}
 317 };
 318
 319 static void __init hung_task_sysctl_init(void)
 320 {
 321         register_sysctl_init("kernel", hung_task_sysctls);
 322 }
 323 #else
 324 #define hung_task_sysctl_init() do { } while (0)
 325 #endif /* CONFIG_SYSCTL */
 326
 327
 328 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 329
 330 void reset_hung_task_detector(void)
 331 {
 332         atomic_set(&reset_hung_task, 1);
 333 }
 334 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 335
 336 static bool hung_detector_suspended;
 337
 338 static int hungtask_pm_notify(struct notifier_block *self,
 339                               unsigned long action, void *hcpu)
 340 {
 341         switch (action) {
 342         case PM_SUSPEND_PREPARE:
 343         case PM_HIBERNATION_PREPARE:
 344         case PM_RESTORE_PREPARE:
 345                 hung_detector_suspended = true;
 346                 break;
 347         case PM_POST_SUSPEND:
 348         case PM_POST_HIBERNATION:
 349         case PM_POST_RESTORE:
 350                 hung_detector_suspended = false;
 351                 break;
 352         default:
 353                 break;
 354         }
 355         return NOTIFY_OK;
 356 }
 357
 358 /*
 359  * kthread which checks for tasks stuck in D state
 360  */
 361 static int watchdog(void *dummy)
 362 {
 363         unsigned long hung_last_checked = jiffies;
 364
 365         set_user_nice(current, 0);
 366
 367         for ( ; ; ) {
 368                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 369                 unsigned long interval = sysctl_hung_task_check_interval_secs;
 370                 long t;
 371
 372                 if (interval == 0)
 373                         interval = timeout;
 374                 interval = min_t(unsigned long, interval, timeout);
 375                 t = hung_timeout_jiffies(hung_last_checked, interval);
 376                 if (t <= 0) {
 377                         if (!atomic_xchg(&reset_hung_task, 0) &&
 378                             !hung_detector_suspended)
 379                                 check_hung_uninterruptible_tasks(timeout);
 380                         hung_last_checked = jiffies;
 381                         continue;
 382                 }
 383                 schedule_timeout_interruptible(t);
 384         }
 385
 386         return 0;
 387 }
 388
 389 static int __init hung_task_init(void)
 390 {
 391         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 392
 393         /* Disable hung task detector on suspend */
 394         pm_notifier(hungtask_pm_notify, 0);
 395
 396         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 397         hung_task_sysctl_init();
 398
 399         return 0;
 400 }
 401 subsys_initcall(hung_task_init);