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/*
* 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/module.h>
#include <linux/sysctl.h>
/*
* Have a reasonable limit on the number of tasks checked:
*/
unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
/*
* Zero means infinite timeout - no checking done:
*/
unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
static unsigned long __read_mostly hung_task_poll_jiffies;
unsigned long __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)
{
sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
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,
};
/*
* Returns seconds, approximately. We don't need nanosecond
* resolution, and we don't need to waste time with a big divide when
* 2^30ns == 1.074s.
*/
static unsigned long get_timestamp(void)
{
int this_cpu = raw_smp_processor_id();
return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
}
static void check_hung_task(struct task_struct *t, unsigned long now,
unsigned long timeout)
{
unsigned long switch_count = t->nvcsw + t->nivcsw;
if (t->flags & PF_FROZEN)
return;
if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
t->last_switch_count = switch_count;
t->last_switch_timestamp = now;
return;
}
if ((long)(now - t->last_switch_timestamp) < timeout)
return;
if (!sysctl_hung_task_warnings)
return;
sysctl_hung_task_warnings--;
/*
* Ok, the task did not get scheduled for more than 2 minutes,
* complain:
*/
printk(KERN_ERR "INFO: task %s:%d blocked for more than "
"%ld seconds.\n", t->comm, t->pid, timeout);
printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
" disables this message.\n");
sched_show_task(t);
__debug_show_held_locks(t);
t->last_switch_timestamp = now;
touch_nmi_watchdog();
if (sysctl_hung_task_panic)
panic("hung_task: blocked tasks");
}
/*
* 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 now = get_timestamp();
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;
read_lock(&tasklist_lock);
do_each_thread(g, t) {
if (!--max_count)
goto unlock;
/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
if (t->state == TASK_UNINTERRUPTIBLE)
check_hung_task(t, now, timeout);
} while_each_thread(g, t);
unlock:
read_unlock(&tasklist_lock);
}
static void update_poll_jiffies(void)
{
/* timeout of 0 will disable the watchdog */
if (sysctl_hung_task_timeout_secs == 0)
hung_task_poll_jiffies = MAX_SCHEDULE_TIMEOUT;
else
hung_task_poll_jiffies = sysctl_hung_task_timeout_secs * HZ / 2;
}
/*
* Process updating of timeout sysctl
*/
int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
struct file *filp, void __user *buffer,
size_t *lenp, loff_t *ppos)
{
int ret;
ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
if (ret || !write)
goto out;
update_poll_jiffies();
wake_up_process(watchdog_task);
out:
return ret;
}
/*
* kthread which checks for tasks stuck in D state
*/
static int watchdog(void *dummy)
{
set_user_nice(current, 0);
update_poll_jiffies();
for ( ; ; ) {
unsigned long timeout;
while (schedule_timeout_interruptible(hung_task_poll_jiffies));
/*
* Need to cache timeout here to avoid timeout being set
* to 0 via sysctl while inside check_hung_*_tasks().
*/
timeout = sysctl_hung_task_timeout_secs;
if (timeout)
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;
}
module_init(hung_task_init);
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