softlockup: decouple hung tasks check from softlockup detection
Mandeep Singh Baines [Thu, 15 Jan 2009 19:08:40 +0000 (11:08 -0800)]
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@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/sched.h
kernel/Makefile
kernel/hung_task.c [new file with mode: 0644]
kernel/softlockup.c
kernel/sysctl.c
lib/Kconfig.debug

index 54cbabf..f2f94d5 100644 (file)
@@ -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;
index 2aebc4c..979745f 100644 (file)
@@ -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 (file)
index 0000000..ba5a77c
--- /dev/null
@@ -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);
index 85d5a24..88796c3 100644 (file)
@@ -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, &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))
index 596dc31..2481ed3 100644 (file)
@@ -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,
        },
        {
index 4c9ae60..883ecea 100644 (file)
@@ -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