| // SPDX-License-Identifier: GPL-2.0-only |
| /* |
| * Detect Hung Task |
| * |
| * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state |
| * |
| */ |
| |
| #include <linux/mm.h> |
| #include <linux/cpu.h> |
| #include <linux/nmi.h> |
| #include <linux/init.h> |
| #include <linux/delay.h> |
| #include <linux/freezer.h> |
| #include <linux/kthread.h> |
| #include <linux/lockdep.h> |
| #include <linux/export.h> |
| #include <linux/panic_notifier.h> |
| #include <linux/sysctl.h> |
| #include <linux/suspend.h> |
| #include <linux/utsname.h> |
| #include <linux/sched/signal.h> |
| #include <linux/sched/debug.h> |
| #include <linux/sched/sysctl.h> |
| |
| #include <trace/events/sched.h> |
| |
| /* |
| * The number of tasks checked: |
| */ |
| int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; |
| |
| /* |
| * Limit number of tasks checked in a batch. |
| * |
| * This value controls the preemptibility of khungtaskd since preemption |
| * is disabled during the critical section. It also controls the size of |
| * the RCU grace period. So it needs to be upper-bound. |
| */ |
| #define HUNG_TASK_LOCK_BREAK (HZ / 10) |
| |
| /* |
| * Zero means infinite timeout - no checking done: |
| */ |
| unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; |
| |
| /* |
| * Zero (default value) means use sysctl_hung_task_timeout_secs: |
| */ |
| unsigned long __read_mostly sysctl_hung_task_check_interval_secs; |
| |
| int __read_mostly sysctl_hung_task_warnings = 10; |
| |
| static int __read_mostly did_panic; |
| static bool hung_task_show_lock; |
| static bool hung_task_call_panic; |
| static bool hung_task_show_all_bt; |
| |
| static struct task_struct *watchdog_task; |
| |
| #ifdef CONFIG_SMP |
| /* |
| * Should we dump all CPUs backtraces in a hung task event? |
| * Defaults to 0, can be changed via sysctl. |
| */ |
| static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace; |
| #else |
| #define sysctl_hung_task_all_cpu_backtrace 0 |
| #endif /* CONFIG_SMP */ |
| |
| /* |
| * Should we panic (and reboot, if panic_timeout= is set) when a |
| * hung task is detected: |
| */ |
| unsigned int __read_mostly sysctl_hung_task_panic = |
| IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC); |
| |
| static int |
| hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) |
| { |
| did_panic = 1; |
| |
| return NOTIFY_DONE; |
| } |
| |
| static struct notifier_block panic_block = { |
| .notifier_call = hung_task_panic, |
| }; |
| |
| static void check_hung_task(struct task_struct *t, unsigned long timeout) |
| { |
| unsigned long switch_count = t->nvcsw + t->nivcsw; |
| |
| /* |
| * Ensure the task is not frozen. |
| * Also, skip vfork and any other user process that freezer should skip. |
| */ |
| if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP))) |
| return; |
| |
| /* |
| * When a freshly created task is scheduled once, changes its state to |
| * TASK_UNINTERRUPTIBLE without having ever been switched out once, it |
| * musn't be checked. |
| */ |
| if (unlikely(!switch_count)) |
| return; |
| |
| if (switch_count != t->last_switch_count) { |
| t->last_switch_count = switch_count; |
| t->last_switch_time = jiffies; |
| return; |
| } |
| if (time_is_after_jiffies(t->last_switch_time + timeout * HZ)) |
| return; |
| |
| trace_sched_process_hang(t); |
| |
| if (sysctl_hung_task_panic) { |
| console_verbose(); |
| hung_task_show_lock = true; |
| hung_task_call_panic = true; |
| } |
| |
| /* |
| * Ok, the task did not get scheduled for more than 2 minutes, |
| * complain: |
| */ |
| if (sysctl_hung_task_warnings) { |
| printk_prefer_direct_enter(); |
| |
| if (sysctl_hung_task_warnings > 0) |
| sysctl_hung_task_warnings--; |
| pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", |
| t->comm, t->pid, (jiffies - t->last_switch_time) / HZ); |
| pr_err(" %s %s %.*s\n", |
| print_tainted(), init_utsname()->release, |
| (int)strcspn(init_utsname()->version, " "), |
| init_utsname()->version); |
| pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" |
| " disables this message.\n"); |
| sched_show_task(t); |
| hung_task_show_lock = true; |
| |
| if (sysctl_hung_task_all_cpu_backtrace) |
| hung_task_show_all_bt = true; |
| |
| printk_prefer_direct_exit(); |
| } |
| |
| touch_nmi_watchdog(); |
| } |
| |
| /* |
| * To avoid extending the RCU grace period for an unbounded amount of time, |
| * periodically exit the critical section and enter a new one. |
| * |
| * For preemptible RCU it is sufficient to call rcu_read_unlock in order |
| * to exit the grace period. For classic RCU, a reschedule is required. |
| */ |
| static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) |
| { |
| bool can_cont; |
| |
| get_task_struct(g); |
| get_task_struct(t); |
| rcu_read_unlock(); |
| cond_resched(); |
| rcu_read_lock(); |
| can_cont = pid_alive(g) && pid_alive(t); |
| put_task_struct(t); |
| put_task_struct(g); |
| |
| return can_cont; |
| } |
| |
| /* |
| * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for |
| * a really long time (120 seconds). If that happens, print out |
| * a warning. |
| */ |
| static void check_hung_uninterruptible_tasks(unsigned long timeout) |
| { |
| int max_count = sysctl_hung_task_check_count; |
| unsigned long last_break = jiffies; |
| struct task_struct *g, *t; |
| |
| /* |
| * If the system crashed already then all bets are off, |
| * do not report extra hung tasks: |
| */ |
| if (test_taint(TAINT_DIE) || did_panic) |
| return; |
| |
| hung_task_show_lock = false; |
| rcu_read_lock(); |
| for_each_process_thread(g, t) { |
| if (!max_count--) |
| goto unlock; |
| if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { |
| if (!rcu_lock_break(g, t)) |
| goto unlock; |
| last_break = jiffies; |
| } |
| /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ |
| if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE) |
| check_hung_task(t, timeout); |
| } |
| unlock: |
| rcu_read_unlock(); |
| if (hung_task_show_lock) { |
| printk_prefer_direct_enter(); |
| debug_show_all_locks(); |
| printk_prefer_direct_exit(); |
| } |
| |
| if (hung_task_show_all_bt) { |
| hung_task_show_all_bt = false; |
| printk_prefer_direct_enter(); |
| trigger_all_cpu_backtrace(); |
| printk_prefer_direct_exit(); |
| } |
| |
| if (hung_task_call_panic) |
| panic("hung_task: blocked tasks"); |
| } |
| |
| static long hung_timeout_jiffies(unsigned long last_checked, |
| unsigned long timeout) |
| { |
| /* timeout of 0 will disable the watchdog */ |
| return timeout ? last_checked - jiffies + timeout * HZ : |
| MAX_SCHEDULE_TIMEOUT; |
| } |
| |
| #ifdef CONFIG_SYSCTL |
| /* |
| * Process updating of timeout sysctl |
| */ |
| static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, |
| void __user *buffer, |
| size_t *lenp, loff_t *ppos) |
| { |
| int ret; |
| |
| ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
| |
| if (ret || !write) |
| goto out; |
| |
| wake_up_process(watchdog_task); |
| |
| out: |
| return ret; |
| } |
| |
| /* |
| * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs |
| * and hung_task_check_interval_secs |
| */ |
| static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ); |
| static struct ctl_table hung_task_sysctls[] = { |
| #ifdef CONFIG_SMP |
| { |
| .procname = "hung_task_all_cpu_backtrace", |
| .data = &sysctl_hung_task_all_cpu_backtrace, |
| .maxlen = sizeof(int), |
| .mode = 0644, |
| .proc_handler = proc_dointvec_minmax, |
| .extra1 = SYSCTL_ZERO, |
| .extra2 = SYSCTL_ONE, |
| }, |
| #endif /* CONFIG_SMP */ |
| { |
| .procname = "hung_task_panic", |
| .data = &sysctl_hung_task_panic, |
| .maxlen = sizeof(int), |
| .mode = 0644, |
| .proc_handler = proc_dointvec_minmax, |
| .extra1 = SYSCTL_ZERO, |
| .extra2 = SYSCTL_ONE, |
| }, |
| { |
| .procname = "hung_task_check_count", |
| .data = &sysctl_hung_task_check_count, |
| .maxlen = sizeof(int), |
| .mode = 0644, |
| .proc_handler = proc_dointvec_minmax, |
| .extra1 = SYSCTL_ZERO, |
| }, |
| { |
| .procname = "hung_task_timeout_secs", |
| .data = &sysctl_hung_task_timeout_secs, |
| .maxlen = sizeof(unsigned long), |
| .mode = 0644, |
| .proc_handler = proc_dohung_task_timeout_secs, |
| .extra2 = (void *)&hung_task_timeout_max, |
| }, |
| { |
| .procname = "hung_task_check_interval_secs", |
| .data = &sysctl_hung_task_check_interval_secs, |
| .maxlen = sizeof(unsigned long), |
| .mode = 0644, |
| .proc_handler = proc_dohung_task_timeout_secs, |
| .extra2 = (void *)&hung_task_timeout_max, |
| }, |
| { |
| .procname = "hung_task_warnings", |
| .data = &sysctl_hung_task_warnings, |
| .maxlen = sizeof(int), |
| .mode = 0644, |
| .proc_handler = proc_dointvec_minmax, |
| .extra1 = SYSCTL_NEG_ONE, |
| }, |
| {} |
| }; |
| |
| static void __init hung_task_sysctl_init(void) |
| { |
| register_sysctl_init("kernel", hung_task_sysctls); |
| } |
| #else |
| #define hung_task_sysctl_init() do { } while (0) |
| #endif /* CONFIG_SYSCTL */ |
| |
| |
| static atomic_t reset_hung_task = ATOMIC_INIT(0); |
| |
| void reset_hung_task_detector(void) |
| { |
| atomic_set(&reset_hung_task, 1); |
| } |
| EXPORT_SYMBOL_GPL(reset_hung_task_detector); |
| |
| static bool hung_detector_suspended; |
| |
| static int hungtask_pm_notify(struct notifier_block *self, |
| unsigned long action, void *hcpu) |
| { |
| switch (action) { |
| case PM_SUSPEND_PREPARE: |
| case PM_HIBERNATION_PREPARE: |
| case PM_RESTORE_PREPARE: |
| hung_detector_suspended = true; |
| break; |
| case PM_POST_SUSPEND: |
| case PM_POST_HIBERNATION: |
| case PM_POST_RESTORE: |
| hung_detector_suspended = false; |
| break; |
| default: |
| break; |
| } |
| return NOTIFY_OK; |
| } |
| |
| /* |
| * kthread which checks for tasks stuck in D state |
| */ |
| static int watchdog(void *dummy) |
| { |
| unsigned long hung_last_checked = jiffies; |
| |
| set_user_nice(current, 0); |
| |
| for ( ; ; ) { |
| unsigned long timeout = sysctl_hung_task_timeout_secs; |
| unsigned long interval = sysctl_hung_task_check_interval_secs; |
| long t; |
| |
| if (interval == 0) |
| interval = timeout; |
| interval = min_t(unsigned long, interval, timeout); |
| t = hung_timeout_jiffies(hung_last_checked, interval); |
| if (t <= 0) { |
| if (!atomic_xchg(&reset_hung_task, 0) && |
| !hung_detector_suspended) |
| check_hung_uninterruptible_tasks(timeout); |
| hung_last_checked = jiffies; |
| continue; |
| } |
| schedule_timeout_interruptible(t); |
| } |
| |
| return 0; |
| } |
| |
| static int __init hung_task_init(void) |
| { |
| atomic_notifier_chain_register(&panic_notifier_list, &panic_block); |
| |
| /* Disable hung task detector on suspend */ |
| pm_notifier(hungtask_pm_notify, 0); |
| |
| watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); |
| hung_task_sysctl_init(); |
| |
| return 0; |
| } |
| subsys_initcall(hung_task_init); |