the-tree/kernel/hung_task.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  * Detect Hung Task
0004  *
0005  * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
0006  *
0007  */
0008
0009 #include <linux/mm.h>
0010 #include <linux/cpu.h>
0011 #include <linux/nmi.h>
0012 #include <linux/init.h>
0013 #include <linux/delay.h>
0014 #include <linux/freezer.h>
0015 #include <linux/kthread.h>
0016 #include <linux/lockdep.h>
0017 #include <linux/export.h>
0018 #include <linux/panic_notifier.h>
0019 #include <linux/sysctl.h>
0020 #include <linux/suspend.h>
0021 #include <linux/utsname.h>
0022 #include <linux/sched/signal.h>
0023 #include <linux/sched/debug.h>
0024 #include <linux/sched/sysctl.h>
0025
0026 #include <trace/events/sched.h>
0027
0028 /*
0029  * The number of tasks checked:
0030  */
0031 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
0032
0033 /*
0034  * Limit number of tasks checked in a batch.
0035  *
0036  * This value controls the preemptibility of khungtaskd since preemption
0037  * is disabled during the critical section. It also controls the size of
0038  * the RCU grace period. So it needs to be upper-bound.
0039  */
0040 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
0041
0042 /*
0043  * Zero means infinite timeout - no checking done:
0044  */
0045 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
0046
0047 /*
0048  * Zero (default value) means use sysctl_hung_task_timeout_secs:
0049  */
0050 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
0051
0052 int __read_mostly sysctl_hung_task_warnings = 10;
0053
0054 static int __read_mostly did_panic;
0055 static bool hung_task_show_lock;
0056 static bool hung_task_call_panic;
0057 static bool hung_task_show_all_bt;
0058
0059 static struct task_struct *watchdog_task;
0060
0061 #ifdef CONFIG_SMP
0062 /*
0063  * Should we dump all CPUs backtraces in a hung task event?
0064  * Defaults to 0, can be changed via sysctl.
0065  */
0066 static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
0067 #else
0068 #define sysctl_hung_task_all_cpu_backtrace 0
0069 #endif /* CONFIG_SMP */
0070
0071 /*
0072  * Should we panic (and reboot, if panic_timeout= is set) when a
0073  * hung task is detected:
0074  */
0075 unsigned int __read_mostly sysctl_hung_task_panic =
0076                 IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
0077
0078 static int
0079 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
0080 {
0081     did_panic = 1;
0082
0083     return NOTIFY_DONE;
0084 }
0085
0086 static struct notifier_block panic_block = {
0087     .notifier_call = hung_task_panic,
0088 };
0089
0090 static void check_hung_task(struct task_struct *t, unsigned long timeout)
0091 {
0092     unsigned long switch_count = t->nvcsw + t->nivcsw;
0093
0094     /*
0095      * Ensure the task is not frozen.
0096      * Also, skip vfork and any other user process that freezer should skip.
0097      */
0098     if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
0099         return;
0100
0101     /*
0102      * When a freshly created task is scheduled once, changes its state to
0103      * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
0104      * musn't be checked.
0105      */
0106     if (unlikely(!switch_count))
0107         return;
0108
0109     if (switch_count != t->last_switch_count) {
0110         t->last_switch_count = switch_count;
0111         t->last_switch_time = jiffies;
0112         return;
0113     }
0114     if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
0115         return;
0116
0117     trace_sched_process_hang(t);
0118
0119     if (sysctl_hung_task_panic) {
0120         console_verbose();
0121         hung_task_show_lock = true;
0122         hung_task_call_panic = true;
0123     }
0124
0125     /*
0126      * Ok, the task did not get scheduled for more than 2 minutes,
0127      * complain:
0128      */
0129     if (sysctl_hung_task_warnings) {
0130         if (sysctl_hung_task_warnings > 0)
0131             sysctl_hung_task_warnings--;
0132         pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
0133                t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
0134         pr_err("      %s %s %.*s\n",
0135             print_tainted(), init_utsname()->release,
0136             (int)strcspn(init_utsname()->version, " "),
0137             init_utsname()->version);
0138         pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
0139             " disables this message.\n");
0140         sched_show_task(t);
0141         hung_task_show_lock = true;
0142
0143         if (sysctl_hung_task_all_cpu_backtrace)
0144             hung_task_show_all_bt = true;
0145     }
0146
0147     touch_nmi_watchdog();
0148 }
0149
0150 /*
0151  * To avoid extending the RCU grace period for an unbounded amount of time,
0152  * periodically exit the critical section and enter a new one.
0153  *
0154  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
0155  * to exit the grace period. For classic RCU, a reschedule is required.
0156  */
0157 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
0158 {
0159     bool can_cont;
0160
0161     get_task_struct(g);
0162     get_task_struct(t);
0163     rcu_read_unlock();
0164     cond_resched();
0165     rcu_read_lock();
0166     can_cont = pid_alive(g) && pid_alive(t);
0167     put_task_struct(t);
0168     put_task_struct(g);
0169
0170     return can_cont;
0171 }
0172
0173 /*
0174  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
0175  * a really long time (120 seconds). If that happens, print out
0176  * a warning.
0177  */
0178 static void check_hung_uninterruptible_tasks(unsigned long timeout)
0179 {
0180     int max_count = sysctl_hung_task_check_count;
0181     unsigned long last_break = jiffies;
0182     struct task_struct *g, *t;
0183
0184     /*
0185      * If the system crashed already then all bets are off,
0186      * do not report extra hung tasks:
0187      */
0188     if (test_taint(TAINT_DIE) || did_panic)
0189         return;
0190
0191     hung_task_show_lock = false;
0192     rcu_read_lock();
0193     for_each_process_thread(g, t) {
0194         if (!max_count--)
0195             goto unlock;
0196         if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
0197             if (!rcu_lock_break(g, t))
0198                 goto unlock;
0199             last_break = jiffies;
0200         }
0201         /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
0202         if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE)
0203             check_hung_task(t, timeout);
0204     }
0205  unlock:
0206     rcu_read_unlock();
0207     if (hung_task_show_lock)
0208         debug_show_all_locks();
0209
0210     if (hung_task_show_all_bt) {
0211         hung_task_show_all_bt = false;
0212         trigger_all_cpu_backtrace();
0213     }
0214
0215     if (hung_task_call_panic)
0216         panic("hung_task: blocked tasks");
0217 }
0218
0219 static long hung_timeout_jiffies(unsigned long last_checked,
0220                  unsigned long timeout)
0221 {
0222     /* timeout of 0 will disable the watchdog */
0223     return timeout ? last_checked - jiffies + timeout * HZ :
0224         MAX_SCHEDULE_TIMEOUT;
0225 }
0226
0227 #ifdef CONFIG_SYSCTL
0228 /*
0229  * Process updating of timeout sysctl
0230  */
0231 static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
0232                   void *buffer,
0233                   size_t *lenp, loff_t *ppos)
0234 {
0235     int ret;
0236
0237     ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
0238
0239     if (ret || !write)
0240         goto out;
0241
0242     wake_up_process(watchdog_task);
0243
0244  out:
0245     return ret;
0246 }
0247
0248 /*
0249  * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
0250  * and hung_task_check_interval_secs
0251  */
0252 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
0253 static struct ctl_table hung_task_sysctls[] = {
0254 #ifdef CONFIG_SMP
0255     {
0256         .procname   = "hung_task_all_cpu_backtrace",
0257         .data       = &sysctl_hung_task_all_cpu_backtrace,
0258         .maxlen     = sizeof(int),
0259         .mode       = 0644,
0260         .proc_handler   = proc_dointvec_minmax,
0261         .extra1     = SYSCTL_ZERO,
0262         .extra2     = SYSCTL_ONE,
0263     },
0264 #endif /* CONFIG_SMP */
0265     {
0266         .procname   = "hung_task_panic",
0267         .data       = &sysctl_hung_task_panic,
0268         .maxlen     = sizeof(int),
0269         .mode       = 0644,
0270         .proc_handler   = proc_dointvec_minmax,
0271         .extra1     = SYSCTL_ZERO,
0272         .extra2     = SYSCTL_ONE,
0273     },
0274     {
0275         .procname   = "hung_task_check_count",
0276         .data       = &sysctl_hung_task_check_count,
0277         .maxlen     = sizeof(int),
0278         .mode       = 0644,
0279         .proc_handler   = proc_dointvec_minmax,
0280         .extra1     = SYSCTL_ZERO,
0281     },
0282     {
0283         .procname   = "hung_task_timeout_secs",
0284         .data       = &sysctl_hung_task_timeout_secs,
0285         .maxlen     = sizeof(unsigned long),
0286         .mode       = 0644,
0287         .proc_handler   = proc_dohung_task_timeout_secs,
0288         .extra2     = (void *)&hung_task_timeout_max,
0289     },
0290     {
0291         .procname   = "hung_task_check_interval_secs",
0292         .data       = &sysctl_hung_task_check_interval_secs,
0293         .maxlen     = sizeof(unsigned long),
0294         .mode       = 0644,
0295         .proc_handler   = proc_dohung_task_timeout_secs,
0296         .extra2     = (void *)&hung_task_timeout_max,
0297     },
0298     {
0299         .procname   = "hung_task_warnings",
0300         .data       = &sysctl_hung_task_warnings,
0301         .maxlen     = sizeof(int),
0302         .mode       = 0644,
0303         .proc_handler   = proc_dointvec_minmax,
0304         .extra1     = SYSCTL_NEG_ONE,
0305     },
0306     {}
0307 };
0308
0309 static void __init hung_task_sysctl_init(void)
0310 {
0311     register_sysctl_init("kernel", hung_task_sysctls);
0312 }
0313 #else
0314 #define hung_task_sysctl_init() do { } while (0)
0315 #endif /* CONFIG_SYSCTL */
0316
0317
0318 static atomic_t reset_hung_task = ATOMIC_INIT(0);
0319
0320 void reset_hung_task_detector(void)
0321 {
0322     atomic_set(&reset_hung_task, 1);
0323 }
0324 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
0325
0326 static bool hung_detector_suspended;
0327
0328 static int hungtask_pm_notify(struct notifier_block *self,
0329                   unsigned long action, void *hcpu)
0330 {
0331     switch (action) {
0332     case PM_SUSPEND_PREPARE:
0333     case PM_HIBERNATION_PREPARE:
0334     case PM_RESTORE_PREPARE:
0335         hung_detector_suspended = true;
0336         break;
0337     case PM_POST_SUSPEND:
0338     case PM_POST_HIBERNATION:
0339     case PM_POST_RESTORE:
0340         hung_detector_suspended = false;
0341         break;
0342     default:
0343         break;
0344     }
0345     return NOTIFY_OK;
0346 }
0347
0348 /*
0349  * kthread which checks for tasks stuck in D state
0350  */
0351 static int watchdog(void *dummy)
0352 {
0353     unsigned long hung_last_checked = jiffies;
0354
0355     set_user_nice(current, 0);
0356
0357     for ( ; ; ) {
0358         unsigned long timeout = sysctl_hung_task_timeout_secs;
0359         unsigned long interval = sysctl_hung_task_check_interval_secs;
0360         long t;
0361
0362         if (interval == 0)
0363             interval = timeout;
0364         interval = min_t(unsigned long, interval, timeout);
0365         t = hung_timeout_jiffies(hung_last_checked, interval);
0366         if (t <= 0) {
0367             if (!atomic_xchg(&reset_hung_task, 0) &&
0368                 !hung_detector_suspended)
0369                 check_hung_uninterruptible_tasks(timeout);
0370             hung_last_checked = jiffies;
0371             continue;
0372         }
0373         schedule_timeout_interruptible(t);
0374     }
0375
0376     return 0;
0377 }
0378
0379 static int __init hung_task_init(void)
0380 {
0381     atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
0382
0383     /* Disable hung task detector on suspend */
0384     pm_notifier(hungtask_pm_notify, 0);
0385
0386     watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
0387     hung_task_sysctl_init();
0388
0389     return 0;
0390 }
0391 subsys_initcall(hung_task_init);