root/kernel/hung_task.c

DEFINITIONS

1. hung_task_panic_setup
2. hung_task_panic
3. check_hung_task
4. rcu_lock_break
5. check_hung_uninterruptible_tasks
6. hung_timeout_jiffies
7. proc_dohung_task_timeout_secs
8. reset_hung_task_detector
9. hungtask_pm_notify
10. watchdog
11. hung_task_init

   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 
  57 static struct task_struct *watchdog_task;
  58 
  59 /*
  60  * Should we panic (and reboot, if panic_timeout= is set) when a
  61  * hung task is detected:
  62  */
  63 unsigned int __read_mostly sysctl_hung_task_panic =
  64                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  65 
  66 static int __init hung_task_panic_setup(char *str)
  67 {
  68         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  69 
  70         if (rc)
  71                 return rc;
  72         return 1;
  73 }
  74 __setup("hung_task_panic=", hung_task_panic_setup);
  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 
 142         touch_nmi_watchdog();
 143 }
 144 
 145 /*
 146  * To avoid extending the RCU grace period for an unbounded amount of time,
 147  * periodically exit the critical section and enter a new one.
 148  *
 149  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 150  * to exit the grace period. For classic RCU, a reschedule is required.
 151  */
 152 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 153 {
 154         bool can_cont;
 155 
 156         get_task_struct(g);
 157         get_task_struct(t);
 158         rcu_read_unlock();
 159         cond_resched();
 160         rcu_read_lock();
 161         can_cont = pid_alive(g) && pid_alive(t);
 162         put_task_struct(t);
 163         put_task_struct(g);
 164 
 165         return can_cont;
 166 }
 167 
 168 /*
 169  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 170  * a really long time (120 seconds). If that happens, print out
 171  * a warning.
 172  */
 173 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 174 {
 175         int max_count = sysctl_hung_task_check_count;
 176         unsigned long last_break = jiffies;
 177         struct task_struct *g, *t;
 178 
 179         /*
 180          * If the system crashed already then all bets are off,
 181          * do not report extra hung tasks:
 182          */
 183         if (test_taint(TAINT_DIE) || did_panic)
 184                 return;
 185 
 186         hung_task_show_lock = false;
 187         rcu_read_lock();
 188         for_each_process_thread(g, t) {
 189                 if (!max_count--)
 190                         goto unlock;
 191                 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
 192                         if (!rcu_lock_break(g, t))
 193                                 goto unlock;
 194                         last_break = jiffies;
 195                 }
 196                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 197                 if (t->state == TASK_UNINTERRUPTIBLE)
 198                         check_hung_task(t, timeout);
 199         }
 200  unlock:
 201         rcu_read_unlock();
 202         if (hung_task_show_lock)
 203                 debug_show_all_locks();
 204         if (hung_task_call_panic) {
 205                 trigger_all_cpu_backtrace();
 206                 panic("hung_task: blocked tasks");
 207         }
 208 }
 209 
 210 static long hung_timeout_jiffies(unsigned long last_checked,
 211                                  unsigned long timeout)
 212 {
 213         /* timeout of 0 will disable the watchdog */
 214         return timeout ? last_checked - jiffies + timeout * HZ :
 215                 MAX_SCHEDULE_TIMEOUT;
 216 }
 217 
 218 /*
 219  * Process updating of timeout sysctl
 220  */
 221 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 222                                   void __user *buffer,
 223                                   size_t *lenp, loff_t *ppos)
 224 {
 225         int ret;
 226 
 227         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 228 
 229         if (ret || !write)
 230                 goto out;
 231 
 232         wake_up_process(watchdog_task);
 233 
 234  out:
 235         return ret;
 236 }
 237 
 238 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 239 
 240 void reset_hung_task_detector(void)
 241 {
 242         atomic_set(&reset_hung_task, 1);
 243 }
 244 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 245 
 246 static bool hung_detector_suspended;
 247 
 248 static int hungtask_pm_notify(struct notifier_block *self,
 249                               unsigned long action, void *hcpu)
 250 {
 251         switch (action) {
 252         case PM_SUSPEND_PREPARE:
 253         case PM_HIBERNATION_PREPARE:
 254         case PM_RESTORE_PREPARE:
 255                 hung_detector_suspended = true;
 256                 break;
 257         case PM_POST_SUSPEND:
 258         case PM_POST_HIBERNATION:
 259         case PM_POST_RESTORE:
 260                 hung_detector_suspended = false;
 261                 break;
 262         default:
 263                 break;
 264         }
 265         return NOTIFY_OK;
 266 }
 267 
 268 /*
 269  * kthread which checks for tasks stuck in D state
 270  */
 271 static int watchdog(void *dummy)
 272 {
 273         unsigned long hung_last_checked = jiffies;
 274 
 275         set_user_nice(current, 0);
 276 
 277         for ( ; ; ) {
 278                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 279                 unsigned long interval = sysctl_hung_task_check_interval_secs;
 280                 long t;
 281 
 282                 if (interval == 0)
 283                         interval = timeout;
 284                 interval = min_t(unsigned long, interval, timeout);
 285                 t = hung_timeout_jiffies(hung_last_checked, interval);
 286                 if (t <= 0) {
 287                         if (!atomic_xchg(&reset_hung_task, 0) &&
 288                             !hung_detector_suspended)
 289                                 check_hung_uninterruptible_tasks(timeout);
 290                         hung_last_checked = jiffies;
 291                         continue;
 292                 }
 293                 schedule_timeout_interruptible(t);
 294         }
 295 
 296         return 0;
 297 }
 298 
 299 static int __init hung_task_init(void)
 300 {
 301         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 302 
 303         /* Disable hung task detector on suspend */
 304         pm_notifier(hungtask_pm_notify, 0);
 305 
 306         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 307 
 308         return 0;
 309 }
 310 subsys_initcall(hung_task_init);