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/sysctl.h>
  19 #include <linux/suspend.h>
  20 #include <linux/utsname.h>
  21 #include <linux/sched/signal.h>
  22 #include <linux/sched/debug.h>
  23 #include <linux/sched/sysctl.h>
  24
  25 #include <trace/events/sched.h>
  26
  27 /*
  28  * The number of tasks checked:
  29  */
  30 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  31
  32 /*
  33  * Limit number of tasks checked in a batch.
  34  *
  35  * This value controls the preemptibility of khungtaskd since preemption
  36  * is disabled during the critical section. It also controls the size of
  37  * the RCU grace period. So it needs to be upper-bound.
  38  */
  39 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
  40
  41 /*
  42  * Zero means infinite timeout - no checking done:
  43  */
  44 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  45
  46 /*
  47  * Zero (default value) means use sysctl_hung_task_timeout_secs:
  48  */
  49 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
  50
  51 int __read_mostly sysctl_hung_task_warnings = 10;
  52
  53 static int __read_mostly did_panic;
  54 static bool hung_task_show_lock;
  55 static bool hung_task_call_panic;
  56 static bool hung_task_show_all_bt;
  57
  58 static struct task_struct *watchdog_task;
  59
  60 #ifdef CONFIG_SMP
  61 /*
  62  * Should we dump all CPUs backtraces in a hung task event?
  63  * Defaults to 0, can be changed via sysctl.
  64  */
  65 unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
  66 #endif /* CONFIG_SMP */
  67
  68 /*
  69  * Should we panic (and reboot, if panic_timeout= is set) when a
  70  * hung task is detected:
  71  */
  72 unsigned int __read_mostly sysctl_hung_task_panic =
  73                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  74
  75 static int
  76 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  77 {
  78         did_panic = 1;
  79
  80         return NOTIFY_DONE;
  81 }
  82
  83 static struct notifier_block panic_block = {
  84         .notifier_call = hung_task_panic,
  85 };
  86
  87 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  88 {
  89         unsigned long switch_count = t->nvcsw + t->nivcsw;
  90
  91         /*
  92          * Ensure the task is not frozen.
  93          * Also, skip vfork and any other user process that freezer should skip.
  94          */
  95         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  96             return;
  97
  98         /*
  99          * When a freshly created task is scheduled once, changes its state to
 100          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
 101          * musn't be checked.
 102          */
 103         if (unlikely(!switch_count))
 104                 return;
 105
 106         if (switch_count != t->last_switch_count) {
 107                 t->last_switch_count = switch_count;
 108                 t->last_switch_time = jiffies;
 109                 return;
 110         }
 111         if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
 112                 return;
 113
 114         trace_sched_process_hang(t);
 115
 116         if (sysctl_hung_task_panic) {
 117                 console_verbose();
 118                 hung_task_show_lock = true;
 119                 hung_task_call_panic = true;
 120         }
 121
 122         /*
 123          * Ok, the task did not get scheduled for more than 2 minutes,
 124          * complain:
 125          */
 126         if (sysctl_hung_task_warnings) {
 127                 if (sysctl_hung_task_warnings > 0)
 128                         sysctl_hung_task_warnings--;
 129                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 130                        t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
 131                 pr_err("      %s %s %.*s\n",
 132                         print_tainted(), init_utsname()->release,
 133                         (int)strcspn(init_utsname()->version, " "),
 134                         init_utsname()->version);
 135                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 136                         " disables this message.\n");
 137                 sched_show_task(t);
 138                 hung_task_show_lock = true;
 139
 140                 if (sysctl_hung_task_all_cpu_backtrace)
 141                         hung_task_show_all_bt = true;
 142         }
 143
 144         touch_nmi_watchdog();
 145 }
 146
 147 /*
 148  * To avoid extending the RCU grace period for an unbounded amount of time,
 149  * periodically exit the critical section and enter a new one.
 150  *
 151  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 152  * to exit the grace period. For classic RCU, a reschedule is required.
 153  */
 154 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 155 {
 156         bool can_cont;
 157
 158         get_task_struct(g);
 159         get_task_struct(t);
 160         rcu_read_unlock();
 161         cond_resched();
 162         rcu_read_lock();
 163         can_cont = pid_alive(g) && pid_alive(t);
 164         put_task_struct(t);
 165         put_task_struct(g);
 166
 167         return can_cont;
 168 }
 169
 170 /*
 171  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 172  * a really long time (120 seconds). If that happens, print out
 173  * a warning.
 174  */
 175 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 176 {
 177         int max_count = sysctl_hung_task_check_count;
 178         unsigned long last_break = jiffies;
 179         struct task_struct *g, *t;
 180
 181         /*
 182          * If the system crashed already then all bets are off,
 183          * do not report extra hung tasks:
 184          */
 185         if (test_taint(TAINT_DIE) || did_panic)
 186                 return;
 187
 188         hung_task_show_lock = false;
 189         rcu_read_lock();
 190         for_each_process_thread(g, t) {
 191                 if (!max_count--)
 192                         goto unlock;
 193                 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
 194                         if (!rcu_lock_break(g, t))
 195                                 goto unlock;
 196                         last_break = jiffies;
 197                 }
 198                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 199                 if (t->state == TASK_UNINTERRUPTIBLE)
 200                         check_hung_task(t, timeout);
 201         }
 202  unlock:
 203         rcu_read_unlock();
 204         if (hung_task_show_lock)
 205                 debug_show_all_locks();
 206
 207         if (hung_task_show_all_bt) {
 208                 hung_task_show_all_bt = false;
 209                 trigger_all_cpu_backtrace();
 210         }
 211
 212         if (hung_task_call_panic)
 213                 panic("hung_task: blocked tasks");
 214 }
 215
 216 static long hung_timeout_jiffies(unsigned long last_checked,
 217                                  unsigned long timeout)
 218 {
 219         /* timeout of 0 will disable the watchdog */
 220         return timeout ? last_checked - jiffies + timeout * HZ :
 221                 MAX_SCHEDULE_TIMEOUT;
 222 }
 223
 224 /*
 225  * Process updating of timeout sysctl
 226  */
 227 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 228                                   void *buffer, size_t *lenp, loff_t *ppos)
 229 {
 230         int ret;
 231
 232         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 233
 234         if (ret || !write)
 235                 goto out;
 236
 237         wake_up_process(watchdog_task);
 238
 239  out:
 240         return ret;
 241 }
 242
 243 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 244
 245 void reset_hung_task_detector(void)
 246 {
 247         atomic_set(&reset_hung_task, 1);
 248 }
 249 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 250
 251 static bool hung_detector_suspended;
 252
 253 static int hungtask_pm_notify(struct notifier_block *self,
 254                               unsigned long action, void *hcpu)
 255 {
 256         switch (action) {
 257         case PM_SUSPEND_PREPARE:
 258         case PM_HIBERNATION_PREPARE:
 259         case PM_RESTORE_PREPARE:
 260                 hung_detector_suspended = true;
 261                 break;
 262         case PM_POST_SUSPEND:
 263         case PM_POST_HIBERNATION:
 264         case PM_POST_RESTORE:
 265                 hung_detector_suspended = false;
 266                 break;
 267         default:
 268                 break;
 269         }
 270         return NOTIFY_OK;
 271 }
 272
 273 /*
 274  * kthread which checks for tasks stuck in D state
 275  */
 276 static int watchdog(void *dummy)
 277 {
 278         unsigned long hung_last_checked = jiffies;
 279
 280         set_user_nice(current, 0);
 281
 282         for ( ; ; ) {
 283                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 284                 unsigned long interval = sysctl_hung_task_check_interval_secs;
 285                 long t;
 286
 287                 if (interval == 0)
 288                         interval = timeout;
 289                 interval = min_t(unsigned long, interval, timeout);
 290                 t = hung_timeout_jiffies(hung_last_checked, interval);
 291                 if (t <= 0) {
 292                         if (!atomic_xchg(&reset_hung_task, 0) &&
 293                             !hung_detector_suspended)
 294                                 check_hung_uninterruptible_tasks(timeout);
 295                         hung_last_checked = jiffies;
 296                         continue;
 297                 }
 298                 schedule_timeout_interruptible(t);
 299         }
 300
 301         return 0;
 302 }
 303
 304 static int __init hung_task_init(void)
 305 {
 306         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 307
 308         /* Disable hung task detector on suspend */
 309         pm_notifier(hungtask_pm_notify, 0);
 310
 311         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 312
 313         return 0;
 314 }
 315 subsys_initcall(hung_task_init);