/* * 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/utsname.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_BATCHING 1024 /* * Zero means infinite timeout - no checking done: */unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; int __read_mostly sysctl_hung_task_warnings = 10; static int __read_mostly did_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 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(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;		return;	} 	trace_sched_process_hang(t); 	if (!sysctl_hung_task_warnings)		return; 	if (sysctl_hung_task_warnings > 0)		sysctl_hung_task_warnings--; 	/*	 * Ok, the task did not get scheduled for more than 2 minutes,	 * complain:	 */	pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",		t->comm, t->pid, timeout);	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);	debug_show_held_locks(t); 	touch_nmi_watchdog(); 	if (sysctl_hung_task_panic) {		trigger_all_cpu_backtrace();		panic("hung_task: blocked tasks");	}} /* * 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;	int batch_count = HUNG_TASK_BATCHING;	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; 	rcu_read_lock();	for_each_process_thread(g, t) {		if (!max_count--)			goto unlock;		if (!--batch_count) {			batch_count = HUNG_TASK_BATCHING;			if (!rcu_lock_break(g, t))				goto unlock;		}		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */		if (t->state == TASK_UNINTERRUPTIBLE)			check_hung_task(t, timeout);	} unlock:	rcu_read_unlock();} static unsigned long timeout_jiffies(unsigned long timeout){	/* timeout of 0 will disable the watchdog */	return timeout ? 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); /* * kthread which checks for tasks stuck in D state */static int watchdog(void *dummy){	set_user_nice(current, 0); 	for ( ; ; ) {		unsigned long timeout = sysctl_hung_task_timeout_secs; 		while (schedule_timeout_interruptible(timeout_jiffies(timeout)))			timeout = sysctl_hung_task_timeout_secs; 		if (atomic_xchg(&reset_hung_task, 0))			continue; 		check_hung_uninterruptible_tasks(timeout);	} 	return 0;} static int __init hung_task_init(void){	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);	watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 	return 0;}subsys_initcall(hung_task_init);