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Subject[PATCH v2] 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
---
include/linux/sched.h | 14 +++++--
kernel/Makefile | 1 +
kernel/softlockup.c | 102 -------------------------------------------------
kernel/sysctl.c | 15 +++++++-
lib/Kconfig.debug | 38 ++++++++++++++++++
5 files changed, 63 insertions(+), 107 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 55e30d1..9e6a39b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -296,9 +296,6 @@ extern void softlockup_tick(void);
extern void touch_softlockup_watchdog(void);
extern void touch_all_softlockup_watchdogs(void);
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)
@@ -315,6 +312,15 @@ 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")))
@@ -1207,7 +1213,7 @@ 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 19fad00..2809bc6 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -70,6 +70,7 @@ 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/softlockup.c b/kernel/softlockup.c
index dc0b3be..8081b88 100644
--- a/kernel/softlockup.c
+++ b/kernel/softlockup.c
@@ -157,97 +157,11 @@ 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 = 120;
-
-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);

@@ -267,11 +181,6 @@ 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);
@@ -303,20 +212,9 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
break;
case CPU_ONLINE:
case CPU_ONLINE_FROZEN:
- check_cpu = any_online_cpu(cpu_online_map);
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) {
- cpumask_t temp_cpu_online_map = cpu_online_map;
-
- cpu_clear(hotcpu, temp_cpu_online_map);
- check_cpu = any_online_cpu(temp_cpu_online_map);
- }
- 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 3d56fe7..51a4748 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -771,6 +771,19 @@ static struct ctl_table kern_table[] = {
.extra1 = &neg_one,
.extra2 = &sixty,
},
+#endif
+#ifdef CONFIG_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",
@@ -786,7 +799,7 @@ 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 b0f239e..a52aa38 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -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
--
1.5.4.5


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