// 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;
/*
* 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 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(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;
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);
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 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);
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