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