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Message-ID: <20090115190840.GA1764@google.com>
Date: Thu, 15 Jan 2009 11:08:40 -0800
From: Mandeep Singh Baines <msb@...gle.com>
To: mingo@...e.hu, hannes@...xchg.org, linux-kernel@...r.kernel.org
Cc: rientjes@...gle.com, mbligh@...gle.com, thockin@...gle.com
Subject: [PATCH v4] softlockup: decouple hung tasks check from softlockup detection
Ingo Molnar (mingo@...e.hu) wrote:
>
> this now conflicts with the softlockup-panic fix you posted - and that fix
> has to go first as it's v2.6.29 material. (while the decoupling patch is
> 2.6.30 material)
>
> So could you please send a patch against tip/master:
>
> http://people.redhat.com/mingo/tip.git/README
>
> Thanks,
>
> Ingo
No problem. Rebased to tip/master.
---
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: Mandeep Singh Baines <msb@...gle.com>
---
include/linux/sched.h | 14 +++-
kernel/Makefile | 1 +
kernel/hung_task.c | 198 +++++++++++++++++++++++++++++++++++++++++++++++++
kernel/softlockup.c | 100 -------------------------
kernel/sysctl.c | 15 ++++-
lib/Kconfig.debug | 38 ++++++++++
6 files changed, 261 insertions(+), 105 deletions(-)
create mode 100644 kernel/hung_task.c
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5a0b9b6..bda891e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -298,9 +298,6 @@ 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)
@@ -317,6 +314,15 @@ 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")))
@@ -1240,7 +1246,7 @@ 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;
diff --git a/kernel/Makefile b/kernel/Makefile
index e411592..46cd2b6 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -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
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
new file mode 100644
index 0000000..ba5a77c
--- /dev/null
+++ b/kernel/hung_task.c
@@ -0,0 +1,198 @@
+/*
+ * 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);
diff --git a/kernel/softlockup.c b/kernel/softlockup.c
index 85d5a24..88796c3 100644
--- a/kernel/softlockup.c
+++ b/kernel/softlockup.c
@@ -166,97 +166,11 @@ void softlockup_tick(void)
}
/*
- * 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, ¶m);
@@ -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))
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 80849e0..d7971f6 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -806,6 +806,19 @@ 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",
@@ -821,7 +834,7 @@ 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,
},
{
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 393eb8c..8ccaf97 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -199,6 +199,44 @@ 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
--
1.5.4.5
--
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