// 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/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 struct task_struct *watchdog_task; /* * Should we panic (and reboot, if panic_timeout= is set) when a * hung task is detected: */ unsigned int __read_mostly sysctl_hung_task_panic = CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; static int __init hung_task_panic_setup(char *str) { int rc = kstrtouint(str, 0, &sysctl_hung_task_panic); if (rc) return rc; return 1; } __setup("hung_task_panic=", hung_task_panic_setup); 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) { 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; } 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 (t->state == TASK_UNINTERRUPTIBLE) check_hung_task(t, timeout); } unlock: rcu_read_unlock(); if (hung_task_show_lock) debug_show_all_locks(); if (hung_task_call_panic) { trigger_all_cpu_backtrace(); 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; } /* * Process updating of timeout sysctl */ 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; } 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"); return 0; } subsys_initcall(hung_task_init);