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
  20 /*
  21  * The number of tasks checked:
  22  */
  23 unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  24
  25 /*
  26  * Limit number of tasks checked in a batch.
  27  *
  28  * This value controls the preemptibility of khungtaskd since preemption
  29  * is disabled during the critical section. It also controls the size of
  30  * the RCU grace period. So it needs to be upper-bound.
  31  */
  32 #define HUNG_TASK_BATCHING 1024
  33
  34 /*
  35  * Zero means infinite timeout - no checking done:
  36  */
  37 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
  38
  39 unsigned long __read_mostly sysctl_hung_task_warnings = 10;
  40
  41 static int __read_mostly did_panic;
  42
  43 static struct task_struct *watchdog_task;
  44
  45 /*
  46  * Should we panic (and reboot, if panic_timeout= is set) when a
  47  * hung task is detected:
  48  */
  49 unsigned int __read_mostly sysctl_hung_task_panic =
  50                                 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
  51
  52 static int __init hung_task_panic_setup(char *str)
  53 {
  54         sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
  55
  56         return 1;
  57 }
  58 __setup("hung_task_panic=", hung_task_panic_setup);
  59
  60 static int
  61 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
  62 {
  63         did_panic = 1;
  64
  65         return NOTIFY_DONE;
  66 }
  67
  68 static struct notifier_block panic_block = {
  69         .notifier_call = hung_task_panic,
  70 };
  71
  72 static void check_hung_task(struct task_struct *t, unsigned long timeout)
  73 {
  74         unsigned long switch_count = t->nvcsw + t->nivcsw;
  75
  76         /*
  77          * Ensure the task is not frozen.
  78          * Also, skip vfork and any other user process that freezer should skip.
  79          */
  80         if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
  81             return;
  82
  83         /*
  84          * When a freshly created task is scheduled once, changes its state to
  85          * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
  86          * musn't be checked.
  87          */
  88         if (unlikely(!switch_count))
  89                 return;
  90
  91         if (switch_count != t->last_switch_count) {
  92                 t->last_switch_count = switch_count;
  93                 return;
  94         }
  95         if (!sysctl_hung_task_warnings)
  96                 return;
  97         sysctl_hung_task_warnings--;
  98
  99         /*
 100          * Ok, the task did not get scheduled for more than 2 minutes,
 101          * complain:
 102          */
 103         pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
 104                 t->comm, t->pid, timeout);
 105         pr_err("      %s %s %.*s\n",
 106                 print_tainted(), init_utsname()->release,
 107                 (int)strcspn(init_utsname()->version, " "),
 108                 init_utsname()->version);
 109         pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 110                 " disables this message.\n");
 111         sched_show_task(t);
 112         debug_show_held_locks(t);
 113
 114         touch_nmi_watchdog();
 115
 116         if (sysctl_hung_task_panic) {
 117                 trigger_all_cpu_backtrace();
 118                 panic("hung_task: blocked tasks");
 119         }
 120 }
 121
 122 /*
 123  * To avoid extending the RCU grace period for an unbounded amount of time,
 124  * periodically exit the critical section and enter a new one.
 125  *
 126  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 127  * to exit the grace period. For classic RCU, a reschedule is required.
 128  */
 129 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
 130 {
 131         bool can_cont;
 132
 133         get_task_struct(g);
 134         get_task_struct(t);
 135         rcu_read_unlock();
 136         cond_resched();
 137         rcu_read_lock();
 138         can_cont = pid_alive(g) && pid_alive(t);
 139         put_task_struct(t);
 140         put_task_struct(g);
 141
 142         return can_cont;
 143 }
 144
 145 /*
 146  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 147  * a really long time (120 seconds). If that happens, print out
 148  * a warning.
 149  */
 150 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 151 {
 152         int max_count = sysctl_hung_task_check_count;
 153         int batch_count = HUNG_TASK_BATCHING;
 154         struct task_struct *g, *t;
 155
 156         /*
 157          * If the system crashed already then all bets are off,
 158          * do not report extra hung tasks:
 159          */
 160         if (test_taint(TAINT_DIE) || did_panic)
 161                 return;
 162
 163         rcu_read_lock();
 164         do_each_thread(g, t) {
 165                 if (!max_count--)
 166                         goto unlock;
 167                 if (!--batch_count) {
 168                         batch_count = HUNG_TASK_BATCHING;
 169                         if (!rcu_lock_break(g, t))
 170                                 goto unlock;
 171                 }
 172                 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 173                 if (t->state == TASK_UNINTERRUPTIBLE)
 174                         check_hung_task(t, timeout);
 175         } while_each_thread(g, t);
 176  unlock:
 177         rcu_read_unlock();
 178 }
 179
 180 static unsigned long timeout_jiffies(unsigned long timeout)
 181 {
 182         /* timeout of 0 will disable the watchdog */
 183         return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
 184 }
 185
 186 /*
 187  * Process updating of timeout sysctl
 188  */
 189 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
 190                                   void __user *buffer,
 191                                   size_t *lenp, loff_t *ppos)
 192 {
 193         int ret;
 194
 195         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 196
 197         if (ret || !write)
 198                 goto out;
 199
 200         wake_up_process(watchdog_task);
 201
 202  out:
 203         return ret;
 204 }
 205
 206 /*
 207  * kthread which checks for tasks stuck in D state
 208  */
 209 static int watchdog(void *dummy)
 210 {
 211         set_user_nice(current, 0);
 212
 213         for ( ; ; ) {
 214                 unsigned long timeout = sysctl_hung_task_timeout_secs;
 215
 216                 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
 217                         timeout = sysctl_hung_task_timeout_secs;
 218
 219                 check_hung_uninterruptible_tasks(timeout);
 220         }
 221
 222         return 0;
 223 }
 224
 225 static int __init hung_task_init(void)
 226 {
 227         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 228         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 229
 230         return 0;
 231 }
 232
 233 module_init(hung_task_init);