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@@ -0,0 +1,217 @@
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+/*
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+ * Detect Hung Task
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+ *
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+ * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
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+ *
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+ */
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+
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+#include <linux/mm.h>
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+#include <linux/cpu.h>
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+#include <linux/nmi.h>
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+#include <linux/init.h>
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+#include <linux/delay.h>
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+#include <linux/freezer.h>
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+#include <linux/kthread.h>
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+#include <linux/lockdep.h>
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+#include <linux/module.h>
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+#include <linux/sysctl.h>
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+
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+/*
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+ * The number of tasks checked:
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+ */
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+unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
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+
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+/*
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+ * Limit number of tasks checked in a batch.
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+ *
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+ * This value controls the preemptibility of khungtaskd since preemption
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+ * is disabled during the critical section. It also controls the size of
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+ * the RCU grace period. So it needs to be upper-bound.
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+ */
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+#define HUNG_TASK_BATCHING 1024
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+
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+/*
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+ * Zero means infinite timeout - no checking done:
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+ */
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+unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
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+
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+unsigned long __read_mostly sysctl_hung_task_warnings = 10;
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+
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+static int __read_mostly did_panic;
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+
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+static struct task_struct *watchdog_task;
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+
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+/*
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+ * Should we panic (and reboot, if panic_timeout= is set) when a
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+ * hung task is detected:
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+ */
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+unsigned int __read_mostly sysctl_hung_task_panic =
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+ CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
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+
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+static int __init hung_task_panic_setup(char *str)
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+{
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+ sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
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+
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+ return 1;
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+}
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+__setup("hung_task_panic=", hung_task_panic_setup);
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+
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+static int
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+hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
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+{
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+ did_panic = 1;
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+
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+ return NOTIFY_DONE;
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+}
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+
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+static struct notifier_block panic_block = {
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+ .notifier_call = hung_task_panic,
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+};
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+
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+static void check_hung_task(struct task_struct *t, unsigned long timeout)
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+{
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+ unsigned long switch_count = t->nvcsw + t->nivcsw;
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+
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+ /*
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+ * Ensure the task is not frozen.
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+ * Also, when a freshly created task is scheduled once, changes
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+ * its state to TASK_UNINTERRUPTIBLE without having ever been
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+ * switched out once, it musn't be checked.
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+ */
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+ if (unlikely(t->flags & PF_FROZEN || !switch_count))
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+ return;
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+
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+ if (switch_count != t->last_switch_count) {
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+ t->last_switch_count = switch_count;
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+ return;
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+ }
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+ if (!sysctl_hung_task_warnings)
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+ return;
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+ sysctl_hung_task_warnings--;
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+
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+ /*
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+ * Ok, the task did not get scheduled for more than 2 minutes,
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+ * complain:
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+ */
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+ printk(KERN_ERR "INFO: task %s:%d blocked for more than "
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+ "%ld seconds.\n", t->comm, t->pid, timeout);
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+ printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
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+ " disables this message.\n");
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+ sched_show_task(t);
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+ __debug_show_held_locks(t);
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+
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+ touch_nmi_watchdog();
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+
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+ if (sysctl_hung_task_panic)
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+ panic("hung_task: blocked tasks");
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+}
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+
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+/*
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+ * To avoid extending the RCU grace period for an unbounded amount of time,
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+ * periodically exit the critical section and enter a new one.
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+ *
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+ * For preemptible RCU it is sufficient to call rcu_read_unlock in order
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+ * exit the grace period. For classic RCU, a reschedule is required.
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+ */
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+static void rcu_lock_break(struct task_struct *g, struct task_struct *t)
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+{
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+ get_task_struct(g);
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+ get_task_struct(t);
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+ rcu_read_unlock();
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+ cond_resched();
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+ rcu_read_lock();
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+ put_task_struct(t);
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+ put_task_struct(g);
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+}
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+
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+/*
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+ * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
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+ * a really long time (120 seconds). If that happens, print out
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+ * a warning.
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+ */
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+static void check_hung_uninterruptible_tasks(unsigned long timeout)
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+{
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+ int max_count = sysctl_hung_task_check_count;
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+ int batch_count = HUNG_TASK_BATCHING;
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+ struct task_struct *g, *t;
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+
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+ /*
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+ * If the system crashed already then all bets are off,
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+ * do not report extra hung tasks:
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+ */
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+ if (test_taint(TAINT_DIE) || did_panic)
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+ return;
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+
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+ rcu_read_lock();
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+ do_each_thread(g, t) {
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+ if (!--max_count)
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+ goto unlock;
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+ if (!--batch_count) {
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+ batch_count = HUNG_TASK_BATCHING;
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+ rcu_lock_break(g, t);
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+ /* Exit if t or g was unhashed during refresh. */
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+ if (t->state == TASK_DEAD || g->state == TASK_DEAD)
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+ goto unlock;
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+ }
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+ /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
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+ if (t->state == TASK_UNINTERRUPTIBLE)
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+ check_hung_task(t, timeout);
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+ } while_each_thread(g, t);
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+ unlock:
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+ rcu_read_unlock();
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+}
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+
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+static unsigned long timeout_jiffies(unsigned long timeout)
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+{
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+ /* timeout of 0 will disable the watchdog */
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+ return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
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+}
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+
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+/*
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+ * Process updating of timeout sysctl
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+ */
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+int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
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+ struct file *filp, void __user *buffer,
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+ size_t *lenp, loff_t *ppos)
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+{
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+ int ret;
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+
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+ ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
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+
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+ if (ret || !write)
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+ goto out;
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+
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+ wake_up_process(watchdog_task);
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+
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+ out:
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+ return ret;
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+}
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+
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+/*
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+ * kthread which checks for tasks stuck in D state
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+ */
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+static int watchdog(void *dummy)
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+{
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+ set_user_nice(current, 0);
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+
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+ for ( ; ; ) {
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+ unsigned long timeout = sysctl_hung_task_timeout_secs;
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+
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+ while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
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+ timeout = sysctl_hung_task_timeout_secs;
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+
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+ check_hung_uninterruptible_tasks(timeout);
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+ }
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+
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+ return 0;
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+}
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+
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+static int __init hung_task_init(void)
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+{
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+ atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
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+ watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
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+
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+ return 0;
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+}
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+
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+module_init(hung_task_init);
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Linus Torvalds