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
  47 static struct task_struct *watchdog_task;
  48
  49 /*
  50  * Should we panic (and reboot, if panic_timeout= is set) when a
  51  * hung task is detected:
  52  */
  53 unsigned int __read_mostly sysctl_hung_task_panic =
  54                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  55
  56 static int __init hung_task_panic_setup(char *str)
  57 {
  58         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  59
  60         if (rc)
  61                 return rc;
  62         return 1;
  63 }
  64 __setup("hung_task_panic=", hung_task_panic_setup);
  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                 return;
 100         }
 101
 102         trace_sched_process_hang(t);
 103
 104         if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
 105                 return;
 106
 107         /*
 108          * Ok, the task did not get scheduled for more than 2 minutes,
 109          * complain:
 110          */
 111         if (sysctl_hung_task_warnings) {
 112                 if (sysctl_hung_task_warnings > 0)
 113                         sysctl_hung_task_warnings--;
 114                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 115                         t->comm, t->pid, timeout);
 116                 pr_err("      %s %s %.*s\n",
 117                         print_tainted(), init_utsname()->release,
 118                         (int)strcspn(init_utsname()->version, " "),
 119                         init_utsname()->version);
 120                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 121                         " disables this message.\n");
 122                 sched_show_task(t);
 123                 debug_show_all_locks();
 124         }
 125
 126         touch_nmi_watchdog();
 127
 128         if (sysctl_hung_task_panic) {
 129                 trigger_all_cpu_backtrace();
 130                 panic("hung_task: blocked tasks");
 131         }
 132 }
 133
 134 /*
 135  * To avoid extending the RCU grace period for an unbounded amount of time,
 136  * periodically exit the critical section and enter a new one.
 137  *
 138  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 139  * to exit the grace period. For classic RCU, a reschedule is required.
 140  */
 141 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 142 {
 143         bool can_cont;
 144
 145         get_task_struct(g);
 146         get_task_struct(t);
 147         rcu_read_unlock();
 148         cond_resched();
 149         rcu_read_lock();
 150         can_cont = pid_alive(g) && pid_alive(t);
 151         put_task_struct(t);
 152         put_task_struct(g);
 153
 154         return can_cont;
 155 }
 156
 157 /*
 158  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 159  * a really long time (120 seconds). If that happens, print out
 160  * a warning.
 161  */
 162 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 163 {
 164         int max_count = sysctl_hung_task_check_count;
 165         int batch_count = HUNG_TASK_BATCHING;
 166         struct task_struct *g, *t;
 167
 168         /*
 169          * If the system crashed already then all bets are off,
 170          * do not report extra hung tasks:
 171          */
 172         if (test_taint(TAINT_DIE) || did_panic)
 173                 return;
 174
 175         rcu_read_lock();
 176         for_each_process_thread(g, t) {
 177                 if (!max_count--)
 178                         goto unlock;
 179                 if (!--batch_count) {
 180                         batch_count = HUNG_TASK_BATCHING;
 181                         if (!rcu_lock_break(g, t))
 182                                 goto unlock;
 183                 }
 184                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 185                 if (t->state == TASK_UNINTERRUPTIBLE)
 186                         check_hung_task(t, timeout);
 187         }
 188  unlock:
 189         rcu_read_unlock();
 190 }
 191
 192 static long hung_timeout_jiffies(unsigned long last_checked,
 193                                  unsigned long timeout)
 194 {
 195         /* timeout of 0 will disable the watchdog */
 196         return timeout ? last_checked - jiffies + timeout * HZ :
 197                 MAX_SCHEDULE_TIMEOUT;
 198 }
 199
 200 /*
 201  * Process updating of timeout sysctl
 202  */
 203 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 204                                   void __user *buffer,
 205                                   size_t *lenp, loff_t *ppos)
 206 {
 207         int ret;
 208
 209         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 210
 211         if (ret || !write)
 212                 goto out;
 213
 214         wake_up_process(watchdog_task);
 215
 216  out:
 217         return ret;
 218 }
 219
 220 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 221
 222 void reset_hung_task_detector(void)
 223 {
 224         atomic_set(&reset_hung_task, 1);
 225 }
 226 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 227
 228 /*
 229  * kthread which checks for tasks stuck in D state
 230  */
 231 static int watchdog(void *dummy)
 232 {
 233         unsigned long hung_last_checked = jiffies;
 234
 235         set_user_nice(current, 0);
 236
 237         for ( ; ; ) {
 238                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 239                 long t = hung_timeout_jiffies(hung_last_checked, timeout);
 240
 241                 if (t <= 0) {
 242                         if (!atomic_xchg(&reset_hung_task, 0))
 243                                 check_hung_uninterruptible_tasks(timeout);
 244                         hung_last_checked = jiffies;
 245                         continue;
 246                 }
 247                 schedule_timeout_interruptible(t);
 248         }
 249
 250         return 0;
 251 }
 252
 253 static int __init hung_task_init(void)
 254 {
 255         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 256         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 257
 258         return 0;
 259 }
 260 subsys_initcall(hung_task_init);