Commit e162b39a authored by Mandeep Singh Baines's avatar Mandeep Singh Baines Committed by Ingo Molnar

softlockup: decouple hung tasks check from softlockup detection

Decoupling allows:

* hung tasks check to happen at very low priority

* hung tasks check and softlockup to be enabled/disabled independently
  at compile and/or run-time

* individual panic settings to be enabled disabled independently
  at compile and/or run-time

* softlockup threshold to be reduced without increasing hung tasks
  poll frequency (hung task check is expensive relative to softlock watchdog)

* hung task check to be zero over-head when disabled at run-time
Signed-off-by: default avatarMandeep Singh Baines <msb@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent c903ff83
......@@ -297,9 +297,6 @@ extern int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
struct file *filp, void __user *buffer,
size_t *lenp, loff_t *ppos);
extern unsigned int softlockup_panic;
extern unsigned long sysctl_hung_task_check_count;
extern unsigned long sysctl_hung_task_timeout_secs;
extern unsigned long sysctl_hung_task_warnings;
extern int softlockup_thresh;
#else
static inline void softlockup_tick(void)
......@@ -316,6 +313,15 @@ static inline void touch_all_softlockup_watchdogs(void)
}
#endif
#ifdef CONFIG_DETECT_HUNG_TASK
extern unsigned int sysctl_hung_task_panic;
extern unsigned long sysctl_hung_task_check_count;
extern unsigned long sysctl_hung_task_timeout_secs;
extern unsigned long sysctl_hung_task_warnings;
extern int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
struct file *filp, void __user *buffer,
size_t *lenp, loff_t *ppos);
#endif
/* Attach to any functions which should be ignored in wchan output. */
#define __sched __attribute__((__section__(".sched.text")))
......@@ -1236,7 +1242,7 @@ struct task_struct {
/* ipc stuff */
struct sysv_sem sysvsem;
#endif
#ifdef CONFIG_DETECT_SOFTLOCKUP
#ifdef CONFIG_DETECT_HUNG_TASK
/* hung task detection */
unsigned long last_switch_timestamp;
unsigned long last_switch_count;
......
......@@ -74,6 +74,7 @@ obj-$(CONFIG_AUDIT_TREE) += audit_tree.o
obj-$(CONFIG_KPROBES) += kprobes.o
obj-$(CONFIG_KGDB) += kgdb.o
obj-$(CONFIG_DETECT_SOFTLOCKUP) += softlockup.o
obj-$(CONFIG_DETECT_HUNG_TASK) += hung_task.o
obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
obj-$(CONFIG_SECCOMP) += seccomp.o
obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
......
/*
* 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 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) <
sysctl_hung_task_timeout_secs)
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,
sysctl_hung_task_timeout_secs);
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(void)
{
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);
} 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 ( ; ; ) {
while (schedule_timeout_interruptible(hung_task_poll_jiffies));
check_hung_uninterruptible_tasks();
}
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);
......@@ -165,98 +165,12 @@ void softlockup_tick(void)
panic("softlockup: hung tasks");
}
/*
* 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 = 480;
unsigned long __read_mostly sysctl_hung_task_warnings = 10;
/*
* Only do the hung-tasks check on one CPU:
*/
static int check_cpu __read_mostly = -1;
static void check_hung_task(struct task_struct *t, unsigned long now)
{
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) <
sysctl_hung_task_timeout_secs)
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,
sysctl_hung_task_timeout_secs);
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 (softlockup_panic)
panic("softlockup: 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(int this_cpu)
{
int max_count = sysctl_hung_task_check_count;
unsigned long now = get_timestamp(this_cpu);
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);
} while_each_thread(g, t);
unlock:
read_unlock(&tasklist_lock);
}
/*
* The watchdog thread - runs every second and touches the timestamp.
*/
static int watchdog(void *__bind_cpu)
{
struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
int this_cpu = (long)__bind_cpu;
sched_setscheduler(current, SCHED_FIFO, &param);
......@@ -276,11 +190,6 @@ static int watchdog(void *__bind_cpu)
if (kthread_should_stop())
break;
if (this_cpu == check_cpu) {
if (sysctl_hung_task_timeout_secs)
check_hung_uninterruptible_tasks(this_cpu);
}
set_current_state(TASK_INTERRUPTIBLE);
}
__set_current_state(TASK_RUNNING);
......@@ -312,18 +221,9 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
break;
case CPU_ONLINE:
case CPU_ONLINE_FROZEN:
check_cpu = cpumask_any(cpu_online_mask);
wake_up_process(per_cpu(watchdog_task, hotcpu));
break;
#ifdef CONFIG_HOTPLUG_CPU
case CPU_DOWN_PREPARE:
case CPU_DOWN_PREPARE_FROZEN:
if (hotcpu == check_cpu) {
/* Pick any other online cpu. */
check_cpu = cpumask_any_but(cpu_online_mask, hotcpu);
}
break;
case CPU_UP_CANCELED:
case CPU_UP_CANCELED_FROZEN:
if (!per_cpu(watchdog_task, hotcpu))
......
......@@ -805,6 +805,19 @@ static struct ctl_table kern_table[] = {
.extra1 = &neg_one,
.extra2 = &sixty,
},
#endif
#ifdef CONFIG_DETECT_HUNG_TASK
{
.ctl_name = CTL_UNNUMBERED,
.procname = "hung_task_panic",
.data = &sysctl_hung_task_panic,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = &proc_dointvec_minmax,
.strategy = &sysctl_intvec,
.extra1 = &zero,
.extra2 = &one,
},
{
.ctl_name = CTL_UNNUMBERED,
.procname = "hung_task_check_count",
......@@ -820,7 +833,7 @@ static struct ctl_table kern_table[] = {
.data = &sysctl_hung_task_timeout_secs,
.maxlen = sizeof(unsigned long),
.mode = 0644,
.proc_handler = &proc_doulongvec_minmax,
.proc_handler = &proc_dohung_task_timeout_secs,
.strategy = &sysctl_intvec,
},
{
......
......@@ -186,6 +186,44 @@ config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC
default 1 if BOOTPARAM_SOFTLOCKUP_PANIC
config DETECT_HUNG_TASK
bool "Detect Hung Tasks"
depends on DEBUG_KERNEL
default y
help
Say Y here to enable the kernel to detect "hung tasks",
which are bugs that cause the task to be stuck in
uninterruptible "D" state indefinitiley.
When a hung task is detected, the kernel will print the
current stack trace (which you should report), but the
task will stay in uninterruptible state. If lockdep is
enabled then all held locks will also be reported. This
feature has negligible overhead.
config BOOTPARAM_HUNG_TASK_PANIC
bool "Panic (Reboot) On Hung Tasks"
depends on DETECT_HUNG_TASK
help
Say Y here to enable the kernel to panic on "hung tasks",
which are bugs that cause the kernel to leave a task stuck
in uninterruptible "D" state.
The panic can be used in combination with panic_timeout,
to cause the system to reboot automatically after a
hung task has been detected. This feature is useful for
high-availability systems that have uptime guarantees and
where a hung tasks must be resolved ASAP.
Say N if unsure.
config BOOTPARAM_HUNG_TASK_PANIC_VALUE
int
depends on DETECT_HUNG_TASK
range 0 1
default 0 if !BOOTPARAM_HUNG_TASK_PANIC
default 1 if BOOTPARAM_HUNG_TASK_PANIC
config SCHED_DEBUG
bool "Collect scheduler debugging info"
depends on DEBUG_KERNEL && PROC_FS
......
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