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