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 <trace/events/sched.h>
  20
  21 /*
  22  * The number of tasks checked:
  23  */
  24 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  25
  26 /*
  27  * Limit number of tasks checked in a batch.
  28  *
  29  * This value controls the preemptibility of khungtaskd since preemption
  30  * is disabled during the critical section. It also controls the size of
  31  * the RCU grace period. So it needs to be upper-bound.
  32  */
  33 #define HUNG_TASK_BATCHING 1024
  34
  35 /*
  36  * Zero means infinite timeout - no checking done:
  37  */
  38 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  39
  40 int __read_mostly sysctl_hung_task_warnings = 10;
  41
  42 static int __read_mostly did_panic;
  43
  44 static struct task_struct *watchdog_task;
  45
  46 /*
  47  * Should we panic (and reboot, if panic_timeout= is set) when a
  48  * hung task is detected:
  49  */
  50 unsigned int __read_mostly sysctl_hung_task_panic =
  51                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  52
  53 static int __init hung_task_panic_setup(char *str)
  54 {
  55         int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
  56
  57         if (rc)
  58                 return rc;
  59         return 1;
  60 }
  61 __setup("hung_task_panic=", hung_task_panic_setup);
  62
  63 static int
  64 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  65 {
  66         did_panic = 1;
  67
  68         return NOTIFY_DONE;
  69 }
  70
  71 static struct notifier_block panic_block = {
  72         .notifier_call = hung_task_panic,
  73 };
  74
  75 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  76 {
  77         unsigned long switch_count = t->nvcsw + t->nivcsw;
  78
  79         /*
  80          * Ensure the task is not frozen.
  81          * Also, skip vfork and any other user process that freezer should skip.
  82          */
  83         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  84             return;
  85
  86         /*
  87          * When a freshly created task is scheduled once, changes its state to
  88          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
  89          * musn't be checked.
  90          */
  91         if (unlikely(!switch_count))
  92                 return;
  93
  94         if (switch_count != t->last_switch_count) {
  95                 t->last_switch_count = switch_count;
  96                 return;
  97         }
  98
  99         trace_sched_process_hang(t);
 100
 101         if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
 102                 return;
 103
 104         /*
 105          * Ok, the task did not get scheduled for more than 2 minutes,
 106          * complain:
 107          */
 108         if (sysctl_hung_task_warnings) {
 109                 if (sysctl_hung_task_warnings > 0)
 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         int batch_count = HUNG_TASK_BATCHING;
 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 (!--batch_count) {
 177                         batch_count = HUNG_TASK_BATCHING;
 178                         if (!rcu_lock_break(g, t))
 179                                 goto unlock;
 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 /*
 226  * kthread which checks for tasks stuck in D state
 227  */
 228 static int watchdog(void *dummy)
 229 {
 230         unsigned long hung_last_checked = jiffies;
 231
 232         set_user_nice(current, 0);
 233
 234         for ( ; ; ) {
 235                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 236                 long t = hung_timeout_jiffies(hung_last_checked, timeout);
 237
 238                 if (t <= 0) {
 239                         if (!atomic_xchg(&reset_hung_task, 0))
 240                                 check_hung_uninterruptible_tasks(timeout);
 241                         hung_last_checked = jiffies;
 242                         continue;
 243                 }
 244                 schedule_timeout_interruptible(t);
 245         }
 246
 247         return 0;
 248 }
 249
 250 static int __init hung_task_init(void)
 251 {
 252         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 253         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 254
 255         return 0;
 256 }
 257 subsys_initcall(hung_task_init);