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 int __read_mostly sysctl_hung_task_warnings = 10;
  44
  45 static int __read_mostly did_panic;
  46 static bool hung_task_show_lock;
  47 static bool hung_task_call_panic;
  48
  49 static struct task_struct *watchdog_task;
  50
  51 /*
  52  * Should we panic (and reboot, if panic_timeout= is set) when a
  53  * hung task is detected:
  54  */
  55 unsigned int __read_mostly sysctl_hung_task_panic =
  56                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  57
  58 static int __init hung_task_panic_setup(char *str)
  59 {
  60         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  61
  62         if (rc)
  63                 return rc;
  64         return 1;
  65 }
  66 __setup("hung_task_panic=", hung_task_panic_setup);
  67
  68 static int
  69 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  70 {
  71         did_panic = 1;
  72
  73         return NOTIFY_DONE;
  74 }
  75
  76 static struct notifier_block panic_block = {
  77         .notifier_call = hung_task_panic,
  78 };
  79
  80 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  81 {
  82         unsigned long switch_count = t->nvcsw + t->nivcsw;
  83
  84         /*
  85          * Ensure the task is not frozen.
  86          * Also, skip vfork and any other user process that freezer should skip.
  87          */
  88         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  89             return;
  90
  91         /*
  92          * When a freshly created task is scheduled once, changes its state to
  93          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
  94          * musn't be checked.
  95          */
  96         if (unlikely(!switch_count))
  97                 return;
  98
  99         if (switch_count != t->last_switch_count) {
 100                 t->last_switch_count = switch_count;
 101                 return;
 102         }
 103
 104         trace_sched_process_hang(t);
 105
 106         if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
 107                 return;
 108
 109         /*
 110          * Ok, the task did not get scheduled for more than 2 minutes,
 111          * complain:
 112          */
 113         if (sysctl_hung_task_warnings) {
 114                 if (sysctl_hung_task_warnings > 0)
 115                         sysctl_hung_task_warnings--;
 116                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 117                         t->comm, t->pid, timeout);
 118                 pr_err("      %s %s %.*s\n",
 119                         print_tainted(), init_utsname()->release,
 120                         (int)strcspn(init_utsname()->version, " "),
 121                         init_utsname()->version);
 122                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 123                         " disables this message.\n");
 124                 sched_show_task(t);
 125                 hung_task_show_lock = true;
 126         }
 127
 128         touch_nmi_watchdog();
 129
 130         if (sysctl_hung_task_panic) {
 131                 hung_task_show_lock = true;
 132                 hung_task_call_panic = true;
 133         }
 134 }
 135
 136 /*
 137  * To avoid extending the RCU grace period for an unbounded amount of time,
 138  * periodically exit the critical section and enter a new one.
 139  *
 140  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 141  * to exit the grace period. For classic RCU, a reschedule is required.
 142  */
 143 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 144 {
 145         bool can_cont;
 146
 147         get_task_struct(g);
 148         get_task_struct(t);
 149         rcu_read_unlock();
 150         cond_resched();
 151         rcu_read_lock();
 152         can_cont = pid_alive(g) && pid_alive(t);
 153         put_task_struct(t);
 154         put_task_struct(g);
 155
 156         return can_cont;
 157 }
 158
 159 /*
 160  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 161  * a really long time (120 seconds). If that happens, print out
 162  * a warning.
 163  */
 164 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 165 {
 166         int max_count = sysctl_hung_task_check_count;
 167         int batch_count = HUNG_TASK_BATCHING;
 168         struct task_struct *g, *t;
 169
 170         /*
 171          * If the system crashed already then all bets are off,
 172          * do not report extra hung tasks:
 173          */
 174         if (test_taint(TAINT_DIE) || did_panic)
 175                 return;
 176
 177         hung_task_show_lock = false;
 178         rcu_read_lock();
 179         for_each_process_thread(g, t) {
 180                 if (!max_count--)
 181                         goto unlock;
 182                 if (!--batch_count) {
 183                         batch_count = HUNG_TASK_BATCHING;
 184                         if (!rcu_lock_break(g, t))
 185                                 goto unlock;
 186                 }
 187                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 188                 if (t->state == TASK_UNINTERRUPTIBLE)
 189                         check_hung_task(t, timeout);
 190         }
 191  unlock:
 192         rcu_read_unlock();
 193         if (hung_task_show_lock)
 194                 debug_show_all_locks();
 195         if (hung_task_call_panic) {
 196                 trigger_all_cpu_backtrace();
 197                 panic("hung_task: blocked tasks");
 198         }
 199 }
 200
 201 static long hung_timeout_jiffies(unsigned long last_checked,
 202                                  unsigned long timeout)
 203 {
 204         /* timeout of 0 will disable the watchdog */
 205         return timeout ? last_checked - jiffies + timeout * HZ :
 206                 MAX_SCHEDULE_TIMEOUT;
 207 }
 208
 209 /*
 210  * Process updating of timeout sysctl
 211  */
 212 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 213                                   void __user *buffer,
 214                                   size_t *lenp, loff_t *ppos)
 215 {
 216         int ret;
 217
 218         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 219
 220         if (ret || !write)
 221                 goto out;
 222
 223         wake_up_process(watchdog_task);
 224
 225  out:
 226         return ret;
 227 }
 228
 229 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 230
 231 void reset_hung_task_detector(void)
 232 {
 233         atomic_set(&reset_hung_task, 1);
 234 }
 235 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 236
 237 /*
 238  * kthread which checks for tasks stuck in D state
 239  */
 240 static int watchdog(void *dummy)
 241 {
 242         unsigned long hung_last_checked = jiffies;
 243
 244         set_user_nice(current, 0);
 245
 246         for ( ; ; ) {
 247                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 248                 long t = hung_timeout_jiffies(hung_last_checked, timeout);
 249
 250                 if (t <= 0) {
 251                         if (!atomic_xchg(&reset_hung_task, 0))
 252                                 check_hung_uninterruptible_tasks(timeout);
 253                         hung_last_checked = jiffies;
 254                         continue;
 255                 }
 256                 schedule_timeout_interruptible(t);
 257         }
 258
 259         return 0;
 260 }
 261
 262 static int __init hung_task_init(void)
 263 {
 264         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 265         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 266
 267         return 0;
 268 }
 269 subsys_initcall(hung_task_init);