kernel/hung_task.c

   1 /*
   2  * Detect Hung Task
   3  *
   4  * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
   5  *
   6  */
   7
   8 #include <linux/mm.h>
   9 #include <linux/cpu.h>
  10 #include <linux/nmi.h>
  11 #include <linux/init.h>
  12 #include <linux/delay.h>
  13 #include <linux/freezer.h>
  14 #include <linux/kthread.h>
  15 #include <linux/lockdep.h>
  16 #include <linux/export.h>
  17 #include <linux/sysctl.h>
  18 #include <linux/suspend.h>
  19 #include <linux/utsname.h>
  20 #include <linux/sched/signal.h>
  21 #include <linux/sched/debug.h>
  22
  23 #include <trace/events/sched.h>
  24
  25 /*
  26  * The number of tasks checked:
  27  */
  28 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  29
  30 /*
  31  * Limit number of tasks checked in a batch.
  32  *
  33  * This value controls the preemptibility of khungtaskd since preemption
  34  * is disabled during the critical section. It also controls the size of
  35  * the RCU grace period. So it needs to be upper-bound.
  36  */
  37 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
  38
  39 /*
  40  * Zero means infinite timeout - no checking done:
  41  */
  42 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  43
  44 /*
  45  * Zero (default value) means use sysctl_hung_task_timeout_secs:
  46  */
  47 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
  48
  49 int __read_mostly sysctl_hung_task_warnings = 10;
  50
  51 static int __read_mostly did_panic;
  52 static bool hung_task_show_lock;
  53 static bool hung_task_call_panic;
  54
  55 static struct task_struct *watchdog_task;
  56
  57 /*
  58  * Should we panic (and reboot, if panic_timeout= is set) when a
  59  * hung task is detected:
  60  */
  61 unsigned int __read_mostly sysctl_hung_task_panic =
  62                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  63
  64 static int __init hung_task_panic_setup(char *str)
  65 {
  66         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  67
  68         if (rc)
  69                 return rc;
  70         return 1;
  71 }
  72 __setup("hung_task_panic=", hung_task_panic_setup);
  73
  74 static int
  75 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  76 {
  77         did_panic = 1;
  78
  79         return NOTIFY_DONE;
  80 }
  81
  82 static struct notifier_block panic_block = {
  83         .notifier_call = hung_task_panic,
  84 };
  85
  86 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  87 {
  88         unsigned long switch_count = t->nvcsw + t->nivcsw;
  89
  90         /*
  91          * Ensure the task is not frozen.
  92          * Also, skip vfork and any other user process that freezer should skip.
  93          */
  94         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  95             return;
  96
  97         /*
  98          * When a freshly created task is scheduled once, changes its state to
  99          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
 100          * musn't be checked.
 101          */
 102         if (unlikely(!switch_count))
 103                 return;
 104
 105         if (switch_count != t->last_switch_count) {
 106                 t->last_switch_count = switch_count;
 107                 t->last_switch_time = jiffies;
 108                 return;
 109         }
 110         if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
 111                 return;
 112
 113         trace_sched_process_hang(t);
 114
 115         if (sysctl_hung_task_panic) {
 116                 console_verbose();
 117                 hung_task_show_lock = true;
 118                 hung_task_call_panic = true;
 119         }
 120
 121         /*
 122          * Ok, the task did not get scheduled for more than 2 minutes,
 123          * complain:
 124          */
 125         if (sysctl_hung_task_warnings) {
 126                 if (sysctl_hung_task_warnings > 0)
 127                         sysctl_hung_task_warnings--;
 128                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 129                         t->comm, t->pid, timeout);
 130                 pr_err("      %s %s %.*s\n",
 131                         print_tainted(), init_utsname()->release,
 132                         (int)strcspn(init_utsname()->version, " "),
 133                         init_utsname()->version);
 134                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 135                         " disables this message.\n");
 136                 sched_show_task(t);
 137                 hung_task_show_lock = true;
 138         }
 139
 140         touch_nmi_watchdog();
 141 }
 142
 143 /*
 144  * To avoid extending the RCU grace period for an unbounded amount of time,
 145  * periodically exit the critical section and enter a new one.
 146  *
 147  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 148  * to exit the grace period. For classic RCU, a reschedule is required.
 149  */
 150 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 151 {
 152         bool can_cont;
 153
 154         get_task_struct(g);
 155         get_task_struct(t);
 156         rcu_read_unlock();
 157         cond_resched();
 158         rcu_read_lock();
 159         can_cont = pid_alive(g) && pid_alive(t);
 160         put_task_struct(t);
 161         put_task_struct(g);
 162
 163         return can_cont;
 164 }
 165
 166 /*
 167  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 168  * a really long time (120 seconds). If that happens, print out
 169  * a warning.
 170  */
 171 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 172 {
 173         int max_count = sysctl_hung_task_check_count;
 174         unsigned long last_break = jiffies;
 175         struct task_struct *g, *t;
 176
 177         /*
 178          * If the system crashed already then all bets are off,
 179          * do not report extra hung tasks:
 180          */
 181         if (test_taint(TAINT_DIE) || did_panic)
 182                 return;
 183
 184         hung_task_show_lock = false;
 185         rcu_read_lock();
 186         for_each_process_thread(g, t) {
 187                 if (!max_count--)
 188                         goto unlock;
 189                 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
 190                         if (!rcu_lock_break(g, t))
 191                                 goto unlock;
 192                         last_break = jiffies;
 193                 }
 194                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 195                 if (t->state == TASK_UNINTERRUPTIBLE)
 196                         check_hung_task(t, timeout);
 197         }
 198  unlock:
 199         rcu_read_unlock();
 200         if (hung_task_show_lock)
 201                 debug_show_all_locks();
 202         if (hung_task_call_panic) {
 203                 trigger_all_cpu_backtrace();
 204                 panic("hung_task: blocked tasks");
 205         }
 206 }
 207
 208 static long hung_timeout_jiffies(unsigned long last_checked,
 209                                  unsigned long timeout)
 210 {
 211         /* timeout of 0 will disable the watchdog */
 212         return timeout ? last_checked - jiffies + timeout * HZ :
 213                 MAX_SCHEDULE_TIMEOUT;
 214 }
 215
 216 /*
 217  * Process updating of timeout sysctl
 218  */
 219 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 220                                   void __user *buffer,
 221                                   size_t *lenp, loff_t *ppos)
 222 {
 223         int ret;
 224
 225         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 226
 227         if (ret || !write)
 228                 goto out;
 229
 230         wake_up_process(watchdog_task);
 231
 232  out:
 233         return ret;
 234 }
 235
 236 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 237
 238 void reset_hung_task_detector(void)
 239 {
 240         atomic_set(&reset_hung_task, 1);
 241 }
 242 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 243
 244 static bool hung_detector_suspended;
 245
 246 static int hungtask_pm_notify(struct notifier_block *self,
 247                               unsigned long action, void *hcpu)
 248 {
 249         switch (action) {
 250         case PM_SUSPEND_PREPARE:
 251         case PM_HIBERNATION_PREPARE:
 252         case PM_RESTORE_PREPARE:
 253                 hung_detector_suspended = true;
 254                 break;
 255         case PM_POST_SUSPEND:
 256         case PM_POST_HIBERNATION:
 257         case PM_POST_RESTORE:
 258                 hung_detector_suspended = false;
 259                 break;
 260         default:
 261                 break;
 262         }
 263         return NOTIFY_OK;
 264 }
 265
 266 /*
 267  * kthread which checks for tasks stuck in D state
 268  */
 269 static int watchdog(void *dummy)
 270 {
 271         unsigned long hung_last_checked = jiffies;
 272
 273         set_user_nice(current, 0);
 274
 275         for ( ; ; ) {
 276                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 277                 unsigned long interval = sysctl_hung_task_check_interval_secs;
 278                 long t;
 279
 280                 if (interval == 0)
 281                         interval = timeout;
 282                 interval = min_t(unsigned long, interval, timeout);
 283                 t = hung_timeout_jiffies(hung_last_checked, interval);
 284                 if (t <= 0) {
 285                         if (!atomic_xchg(&reset_hung_task, 0) &&
 286                             !hung_detector_suspended)
 287                                 check_hung_uninterruptible_tasks(timeout);
 288                         hung_last_checked = jiffies;
 289                         continue;
 290                 }
 291                 schedule_timeout_interruptible(t);
 292         }
 293
 294         return 0;
 295 }
 296
 297 static int __init hung_task_init(void)
 298 {
 299         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 300
 301         /* Disable hung task detector on suspend */
 302         pm_notifier(hungtask_pm_notify, 0);
 303
 304         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 305
 306         return 0;
 307 }
 308 subsys_initcall(hung_task_init);