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 unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
  67 #endif /* CONFIG_SMP */
  68
  69 /*
  70  * Should we panic (and reboot, if panic_timeout= is set) when a
  71  * hung task is detected:
  72  */
  73 unsigned int __read_mostly sysctl_hung_task_panic =
  74                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  75
  76 static int
  77 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  78 {
  79         did_panic = 1;
  80
  81         return NOTIFY_DONE;
  82 }
  83
  84 static struct notifier_block panic_block = {
  85         .notifier_call = hung_task_panic,
  86 };
  87
  88 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  89 {
  90         unsigned long switch_count = t->nvcsw + t->nivcsw;
  91
  92         /*
  93          * Ensure the task is not frozen.
  94          * Also, skip vfork and any other user process that freezer should skip.
  95          */
  96         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  97             return;
  98
  99         /*
 100          * When a freshly created task is scheduled once, changes its state to
 101          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
 102          * musn't be checked.
 103          */
 104         if (unlikely(!switch_count))
 105                 return;
 106
 107         if (switch_count != t->last_switch_count) {
 108                 t->last_switch_count = switch_count;
 109                 t->last_switch_time = jiffies;
 110                 return;
 111         }
 112         if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
 113                 return;
 114
 115         trace_sched_process_hang(t);
 116
 117         if (sysctl_hung_task_panic) {
 118                 console_verbose();
 119                 hung_task_show_lock = true;
 120                 hung_task_call_panic = true;
 121         }
 122
 123         /*
 124          * Ok, the task did not get scheduled for more than 2 minutes,
 125          * complain:
 126          */
 127         if (sysctl_hung_task_warnings) {
 128                 if (sysctl_hung_task_warnings > 0)
 129                         sysctl_hung_task_warnings--;
 130                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 131                        t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
 132                 pr_err("      %s %s %.*s\n",
 133                         print_tainted(), init_utsname()->release,
 134                         (int)strcspn(init_utsname()->version, " "),
 135                         init_utsname()->version);
 136                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 137                         " disables this message.\n");
 138                 sched_show_task(t);
 139                 hung_task_show_lock = true;
 140
 141                 if (sysctl_hung_task_all_cpu_backtrace)
 142                         hung_task_show_all_bt = true;
 143         }
 144
 145         touch_nmi_watchdog();
 146 }
 147
 148 /*
 149  * To avoid extending the RCU grace period for an unbounded amount of time,
 150  * periodically exit the critical section and enter a new one.
 151  *
 152  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 153  * to exit the grace period. For classic RCU, a reschedule is required.
 154  */
 155 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 156 {
 157         bool can_cont;
 158
 159         get_task_struct(g);
 160         get_task_struct(t);
 161         rcu_read_unlock();
 162         cond_resched();
 163         rcu_read_lock();
 164         can_cont = pid_alive(g) && pid_alive(t);
 165         put_task_struct(t);
 166         put_task_struct(g);
 167
 168         return can_cont;
 169 }
 170
 171 /*
 172  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 173  * a really long time (120 seconds). If that happens, print out
 174  * a warning.
 175  */
 176 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 177 {
 178         int max_count = sysctl_hung_task_check_count;
 179         unsigned long last_break = jiffies;
 180         struct task_struct *g, *t;
 181
 182         /*
 183          * If the system crashed already then all bets are off,
 184          * do not report extra hung tasks:
 185          */
 186         if (test_taint(TAINT_DIE) || did_panic)
 187                 return;
 188
 189         hung_task_show_lock = false;
 190         rcu_read_lock();
 191         for_each_process_thread(g, t) {
 192                 if (!max_count--)
 193                         goto unlock;
 194                 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
 195                         if (!rcu_lock_break(g, t))
 196                                 goto unlock;
 197                         last_break = jiffies;
 198                 }
 199                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 200                 if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE)
 201                         check_hung_task(t, timeout);
 202         }
 203  unlock:
 204         rcu_read_unlock();
 205         if (hung_task_show_lock)
 206                 debug_show_all_locks();
 207
 208         if (hung_task_show_all_bt) {
 209                 hung_task_show_all_bt = false;
 210                 trigger_all_cpu_backtrace();
 211         }
 212
 213         if (hung_task_call_panic)
 214                 panic("hung_task: blocked tasks");
 215 }
 216
 217 static long hung_timeout_jiffies(unsigned long last_checked,
 218                                  unsigned long timeout)
 219 {
 220         /* timeout of 0 will disable the watchdog */
 221         return timeout ? last_checked - jiffies + timeout * HZ :
 222                 MAX_SCHEDULE_TIMEOUT;
 223 }
 224
 225 /*
 226  * Process updating of timeout sysctl
 227  */
 228 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 229                                   void *buffer, size_t *lenp, loff_t *ppos)
 230 {
 231         int ret;
 232
 233         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 234
 235         if (ret || !write)
 236                 goto out;
 237
 238         wake_up_process(watchdog_task);
 239
 240  out:
 241         return ret;
 242 }
 243
 244 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 245
 246 void reset_hung_task_detector(void)
 247 {
 248         atomic_set(&reset_hung_task, 1);
 249 }
 250 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 251
 252 static bool hung_detector_suspended;
 253
 254 static int hungtask_pm_notify(struct notifier_block *self,
 255                               unsigned long action, void *hcpu)
 256 {
 257         switch (action) {
 258         case PM_SUSPEND_PREPARE:
 259         case PM_HIBERNATION_PREPARE:
 260         case PM_RESTORE_PREPARE:
 261                 hung_detector_suspended = true;
 262                 break;
 263         case PM_POST_SUSPEND:
 264         case PM_POST_HIBERNATION:
 265         case PM_POST_RESTORE:
 266                 hung_detector_suspended = false;
 267                 break;
 268         default:
 269                 break;
 270         }
 271         return NOTIFY_OK;
 272 }
 273
 274 /*
 275  * kthread which checks for tasks stuck in D state
 276  */
 277 static int watchdog(void *dummy)
 278 {
 279         unsigned long hung_last_checked = jiffies;
 280
 281         set_user_nice(current, 0);
 282
 283         for ( ; ; ) {
 284                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 285                 unsigned long interval = sysctl_hung_task_check_interval_secs;
 286                 long t;
 287
 288                 if (interval == 0)
 289                         interval = timeout;
 290                 interval = min_t(unsigned long, interval, timeout);
 291                 t = hung_timeout_jiffies(hung_last_checked, interval);
 292                 if (t <= 0) {
 293                         if (!atomic_xchg(&reset_hung_task, 0) &&
 294                             !hung_detector_suspended)
 295                                 check_hung_uninterruptible_tasks(timeout);
 296                         hung_last_checked = jiffies;
 297                         continue;
 298                 }
 299                 schedule_timeout_interruptible(t);
 300         }
 301
 302         return 0;
 303 }
 304
 305 static int __init hung_task_init(void)
 306 {
 307         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 308
 309         /* Disable hung task detector on suspend */
 310         pm_notifier(hungtask_pm_notify, 0);
 311
 312         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 313
 314         return 0;
 315 }
 316 subsys_initcall(hung_task_init);