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