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/suspend.h>
  19 #include <linux/utsname.h>
  20 #include <trace/events/sched.h>
  21
  22 /*
  23  * The number of tasks checked:
  24  */
  25 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  26
  27 /*
  28  * Limit number of tasks checked in a batch.
  29  *
  30  * This value controls the preemptibility of khungtaskd since preemption
  31  * is disabled during the critical section. It also controls the size of
  32  * the RCU grace period. So it needs to be upper-bound.
  33  */
  34 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
  35
  36 /*
  37  * Zero means infinite timeout - no checking done:
  38  */
  39 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  40
  41 int __read_mostly sysctl_hung_task_warnings = 10;
  42
  43 static int __read_mostly did_panic;
  44
  45 static struct task_struct *watchdog_task;
  46
  47 /*
  48  * Should we panic (and reboot, if panic_timeout= is set) when a
  49  * hung task is detected:
  50  */
  51 unsigned int __read_mostly sysctl_hung_task_panic =
  52                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  53
  54 static int __init hung_task_panic_setup(char *str)
  55 {
  56         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  57
  58         if (rc)
  59                 return rc;
  60         return 1;
  61 }
  62 __setup("hung_task_panic=", hung_task_panic_setup);
  63
  64 static int
  65 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  66 {
  67         did_panic = 1;
  68
  69         return NOTIFY_DONE;
  70 }
  71
  72 static struct notifier_block panic_block = {
  73         .notifier_call = hung_task_panic,
  74 };
  75
  76 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  77 {
  78         unsigned long switch_count = t->nvcsw + t->nivcsw;
  79
  80         /*
  81          * Ensure the task is not frozen.
  82          * Also, skip vfork and any other user process that freezer should skip.
  83          */
  84         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  85             return;
  86
  87         /*
  88          * When a freshly created task is scheduled once, changes its state to
  89          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
  90          * musn't be checked.
  91          */
  92         if (unlikely(!switch_count))
  93                 return;
  94
  95         if (switch_count != t->last_switch_count) {
  96                 t->last_switch_count = switch_count;
  97                 return;
  98         }
  99
 100         trace_sched_process_hang(t);
 101
 102         if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
 103                 return;
 104
 105         /*
 106          * Ok, the task did not get scheduled for more than 2 minutes,
 107          * complain:
 108          */
 109         if (sysctl_hung_task_warnings) {
 110                 sysctl_hung_task_warnings--;
 111                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 112                         t->comm, t->pid, timeout);
 113                 pr_err("      %s %s %.*s\n",
 114                         print_tainted(), init_utsname()->release,
 115                         (int)strcspn(init_utsname()->version, " "),
 116                         init_utsname()->version);
 117                 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 118                         " disables this message.\n");
 119                 sched_show_task(t);
 120                 debug_show_all_locks();
 121         }
 122
 123         touch_nmi_watchdog();
 124
 125         if (sysctl_hung_task_panic) {
 126                 trigger_all_cpu_backtrace();
 127                 panic("hung_task: blocked tasks");
 128         }
 129 }
 130
 131 /*
 132  * To avoid extending the RCU grace period for an unbounded amount of time,
 133  * periodically exit the critical section and enter a new one.
 134  *
 135  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 136  * to exit the grace period. For classic RCU, a reschedule is required.
 137  */
 138 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 139 {
 140         bool can_cont;
 141
 142         get_task_struct(g);
 143         get_task_struct(t);
 144         rcu_read_unlock();
 145         cond_resched();
 146         rcu_read_lock();
 147         can_cont = pid_alive(g) && pid_alive(t);
 148         put_task_struct(t);
 149         put_task_struct(g);
 150
 151         return can_cont;
 152 }
 153
 154 /*
 155  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 156  * a really long time (120 seconds). If that happens, print out
 157  * a warning.
 158  */
 159 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 160 {
 161         int max_count = sysctl_hung_task_check_count;
 162         unsigned long last_break = jiffies;
 163         struct task_struct *g, *t;
 164
 165         /*
 166          * If the system crashed already then all bets are off,
 167          * do not report extra hung tasks:
 168          */
 169         if (test_taint(TAINT_DIE) || did_panic)
 170                 return;
 171
 172         rcu_read_lock();
 173         for_each_process_thread(g, t) {
 174                 if (!max_count--)
 175                         goto unlock;
 176                 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
 177                         if (!rcu_lock_break(g, t))
 178                                 goto unlock;
 179                         last_break = jiffies;
 180                 }
 181                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 182                 if (t->state == TASK_UNINTERRUPTIBLE)
 183                         check_hung_task(t, timeout);
 184         }
 185  unlock:
 186         rcu_read_unlock();
 187 }
 188
 189 static long hung_timeout_jiffies(unsigned long last_checked,
 190                                  unsigned long timeout)
 191 {
 192         /* timeout of 0 will disable the watchdog */
 193         return timeout ? last_checked - jiffies + timeout * HZ :
 194                 MAX_SCHEDULE_TIMEOUT;
 195 }
 196
 197 /*
 198  * Process updating of timeout sysctl
 199  */
 200 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 201                                   void __user *buffer,
 202                                   size_t *lenp, loff_t *ppos)
 203 {
 204         int ret;
 205
 206         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 207
 208         if (ret || !write)
 209                 goto out;
 210
 211         wake_up_process(watchdog_task);
 212
 213  out:
 214         return ret;
 215 }
 216
 217 static atomic_t reset_hung_task = ATOMIC_INIT(0);
 218
 219 void reset_hung_task_detector(void)
 220 {
 221         atomic_set(&reset_hung_task, 1);
 222 }
 223 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 224
 225 static bool hung_detector_suspended;
 226
 227 static int hungtask_pm_notify(struct notifier_block *self,
 228                               unsigned long action, void *hcpu)
 229 {
 230         switch (action) {
 231         case PM_SUSPEND_PREPARE:
 232         case PM_HIBERNATION_PREPARE:
 233         case PM_RESTORE_PREPARE:
 234                 hung_detector_suspended = true;
 235                 break;
 236         case PM_POST_SUSPEND:
 237         case PM_POST_HIBERNATION:
 238         case PM_POST_RESTORE:
 239                 hung_detector_suspended = false;
 240                 break;
 241         default:
 242                 break;
 243         }
 244         return NOTIFY_OK;
 245 }
 246
 247 /*
 248  * kthread which checks for tasks stuck in D state
 249  */
 250 static int watchdog(void *dummy)
 251 {
 252         unsigned long hung_last_checked = jiffies;
 253
 254         set_user_nice(current, 0);
 255
 256         for ( ; ; ) {
 257                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 258                 long t = hung_timeout_jiffies(hung_last_checked, timeout);
 259
 260                 if (t <= 0) {
 261                         if (!atomic_xchg(&reset_hung_task, 0) &&
 262                             !hung_detector_suspended)
 263                                 check_hung_uninterruptible_tasks(timeout);
 264                         hung_last_checked = jiffies;
 265                         continue;
 266                 }
 267                 schedule_timeout_interruptible(t);
 268         }
 269
 270         return 0;
 271 }
 272
 273 static int __init hung_task_init(void)
 274 {
 275         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 276
 277         /* Disable hung task detector on suspend */
 278         pm_notifier(hungtask_pm_notify, 0);
 279
 280         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 281
 282         return 0;
 283 }
 284 subsys_initcall(hung_task_init);