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/utsname.h>
  19 #include <linux/sched/signal.h>
  20 #include <linux/sched/debug.h>
  21
  22 #include <trace/events/sched.h>
  23
  24 /*
  25  * The number of tasks checked:
  26  */
  27 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  28
  29 /*
  30  * Limit number of tasks checked in a batch.
  31  *
  32  * This value controls the preemptibility of khungtaskd since preemption
  33  * is disabled during the critical section. It also controls the size of
  34  * the RCU grace period. So it needs to be upper-bound.
  35  */
  36 #define HUNG_TASK_BATCHING 1024
  37
  38 /*
  39  * Zero means infinite timeout - no checking done:
  40  */
  41 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  42
  43 /*
  44  * Zero (default value) means use sysctl_hung_task_timeout_secs:
  45  */
  46 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
  47
  48 int __read_mostly sysctl_hung_task_warnings = 10;
  49
  50 static int __read_mostly did_panic;
  51 static bool hung_task_show_lock;
  52 static bool hung_task_call_panic;
  53
  54 static struct task_struct *watchdog_task;
  55
  56 /*
  57  * Should we panic (and reboot, if panic_timeout= is set) when a
  58  * hung task is detected:
  59  */
  60 unsigned int __read_mostly sysctl_hung_task_panic =
  61                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  62
  63 static int __init hung_task_panic_setup(char *str)
  64 {
  65         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  66
  67         if (rc)
  68                 return rc;
  69         return 1;
  70 }
  71 __setup("hung_task_panic=", hung_task_panic_setup);
  72
  73 static int
  74 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  75 {
  76         did_panic = 1;
  77
  78         return NOTIFY_DONE;
  79 }
  80
  81 static struct notifier_block panic_block = {
  82         .notifier_call = hung_task_panic,
  83 };
  84
  85 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  86 {
  87         unsigned long switch_count = t->nvcsw + t->nivcsw;
  88
  89         /*
  90          * Ensure the task is not frozen.
  91          * Also, skip vfork and any other user process that freezer should skip.
  92          */
  93         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  94             return;
  95
  96         /*
  97          * When a freshly created task is scheduled once, changes its state to
  98          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
  99          * musn't be checked.
 100          */
 101         if (unlikely(!switch_count))
 102                 return;
 103
 104         if (switch_count != t->last_switch_count) {
 105                 t->last_switch_count = switch_count;
 106                 t->last_switch_time = jiffies;
 107                 return;
 108         }
 109         if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
 110                 return;
 111
 112         trace_sched_process_hang(t);
 113
 114         if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
 115                 return;
 116
 117         /*
 118          * Ok, the task did not get scheduled for more than 2 minutes,
 119          * complain:
 120          */
 121         if (sysctl_hung_task_warnings) {
 122                 if (sysctl_hung_task_warnings > 0)
 123                         sysctl_hung_task_warnings--;
 124                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 125                         t->comm, t->pid, timeout);
 126                 pr_err("      %s %s %.*s\n",
 127                         print_tainted(), init_utsname()->release,
 128                         (int)strcspn(init_utsname()->version, " "),
 129                         init_utsname()->version);
 130                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 131                         " disables this message.\n");
 132                 sched_show_task(t);
 133                 hung_task_show_lock = true;
 134         }
 135
 136         touch_nmi_watchdog();
 137
 138         if (sysctl_hung_task_panic) {
 139                 hung_task_show_lock = true;
 140                 hung_task_call_panic = true;
 141         }
 142 }
 143
 144 /*
 145  * To avoid extending the RCU grace period for an unbounded amount of time,
 146  * periodically exit the critical section and enter a new one.
 147  *
 148  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 149  * to exit the grace period. For classic RCU, a reschedule is required.
 150  */
 151 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 152 {
 153         bool can_cont;
 154
 155         get_task_struct(g);
 156         get_task_struct(t);
 157         rcu_read_unlock();
 158         cond_resched();
 159         rcu_read_lock();
 160         can_cont = pid_alive(g) && pid_alive(t);
 161         put_task_struct(t);
 162         put_task_struct(g);
 163
 164         return can_cont;
 165 }
 166
 167 /*
 168  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 169  * a really long time (120 seconds). If that happens, print out
 170  * a warning.
 171  */
 172 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 173 {
 174         int max_count = sysctl_hung_task_check_count;
 175         int batch_count = HUNG_TASK_BATCHING;
 176         struct task_struct *g, *t;
 177
 178         /*
 179          * If the system crashed already then all bets are off,
 180          * do not report extra hung tasks:
 181          */
 182         if (test_taint(TAINT_DIE) || did_panic)
 183                 return;
 184
 185         hung_task_show_lock = false;
 186         rcu_read_lock();
 187         for_each_process_thread(g, t) {
 188                 if (!max_count--)
 189                         goto unlock;
 190                 if (!--batch_count) {
 191                         batch_count = HUNG_TASK_BATCHING;
 192                         if (!rcu_lock_break(g, t))
 193                                 goto unlock;
 194                 }
 195                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 196                 if (t->state == TASK_UNINTERRUPTIBLE)
 197                         check_hung_task(t, timeout);
 198         }
 199  unlock:
 200         rcu_read_unlock();
 201         if (hung_task_show_lock)
 202                 debug_show_all_locks();
 203         if (hung_task_call_panic) {
 204                 trigger_all_cpu_backtrace();
 205                 panic("hung_task: blocked tasks");
 206         }
 207 }
 208
 209 static long hung_timeout_jiffies(unsigned long last_checked,
 210                                  unsigned long timeout)
 211 {
 212         /* timeout of 0 will disable the watchdog */
 213         return timeout ? last_checked - jiffies + timeout * HZ :
 214                 MAX_SCHEDULE_TIMEOUT;
 215 }
 216
 217 /*
 218  * Process updating of timeout sysctl
 219  */
 220 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 221                                   void __user *buffer,
 222                                   size_t *lenp, loff_t *ppos)
 223 {
 224         int ret;
 225
 226         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 227
 228         if (ret || !write)
 229                 goto out;
 230
 231         wake_up_process(watchdog_task);
 232
 233  out:
 234         return ret;
 235 }
 236
 237 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 238
 239 void reset_hung_task_detector(void)
 240 {
 241         atomic_set(&reset_hung_task, 1);
 242 }
 243 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 244
 245 /*
 246  * kthread which checks for tasks stuck in D state
 247  */
 248 static int watchdog(void *dummy)
 249 {
 250         unsigned long hung_last_checked = jiffies;
 251
 252         set_user_nice(current, 0);
 253
 254         for ( ; ; ) {
 255                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 256                 unsigned long interval = sysctl_hung_task_check_interval_secs;
 257                 long t;
 258
 259                 if (interval == 0)
 260                         interval = timeout;
 261                 interval = min_t(unsigned long, interval, timeout);
 262                 t = hung_timeout_jiffies(hung_last_checked, interval);
 263                 if (t <= 0) {
 264                         if (!atomic_xchg(&reset_hung_task, 0))
 265                                 check_hung_uninterruptible_tasks(timeout);
 266                         hung_last_checked = jiffies;
 267                         continue;
 268                 }
 269                 schedule_timeout_interruptible(t);
 270         }
 271
 272         return 0;
 273 }
 274
 275 static int __init hung_task_init(void)
 276 {
 277         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 278         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 279
 280         return 0;
 281 }
 282 subsys_initcall(hung_task_init);