// 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: */static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; /* * Total number of tasks detected as hung since boot: */static unsigned long __read_mostly sysctl_hung_task_detect_count; /* * 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;EXPORT_SYMBOL_GPL(sysctl_hung_task_timeout_secs); /* * Zero (default value) means use sysctl_hung_task_timeout_secs: */static unsigned long __read_mostly sysctl_hung_task_check_interval_secs; static 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: */static unsigned int __read_mostly sysctl_hung_task_panic =	IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC); static inthung_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(READ_ONCE(t->__state) & TASK_FROZEN))		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; 	/*	 * This counter tracks the total number of tasks detected as hung	 * since boot.	 */	sysctl_hung_task_detect_count++; 	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 || hung_task_call_panic) {		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);		if (t->flags & PF_POSTCOREDUMP)			pr_err("      Blocked by coredump.\n");		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;		if (!sysctl_hung_task_warnings)			pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");	} 	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) {		unsigned int state; 		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;		}		/*		 * skip the TASK_KILLABLE tasks -- these can be killed		 * skip the TASK_IDLE tasks -- those are genuinely idle		 */		state = READ_ONCE(t->__state);		if ((state & TASK_UNINTERRUPTIBLE) &&		    !(state & TASK_WAKEKILL) &&		    !(state & TASK_NOLOAD))			check_hung_task(t, timeout);	} unlock:	rcu_read_unlock();	if (hung_task_show_lock)		debug_show_all_locks(); 	if (hung_task_show_all_bt) {		hung_task_show_all_bt = false;		trigger_all_cpu_backtrace();	} 	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(const struct ctl_table *table, int write,				  void *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 const 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,	},	{		.procname	= "hung_task_detect_count",		.data		= &sysctl_hung_task_detect_count,		.maxlen		= sizeof(unsigned long),		.mode		= 0444,		.proc_handler	= proc_doulongvec_minmax,	},}; 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);