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authorMandeep Singh Baines <msb@google.com>2009-01-15 19:08:40 (GMT)
committerIngo Molnar <mingo@elte.hu>2009-01-16 13:06:04 (GMT)
commite162b39a368f0401e41b558f430c354d12a85b37 (patch)
tree3fb7e4d48f398d62e5074e7e3dd183cc54f59820 /kernel/hung_task.c
parentc903ff837909ccada51243307d4239f86af40179 (diff)
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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: Mandeep Singh Baines <msb@google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/hung_task.c')
-rw-r--r--kernel/hung_task.c198
1 files changed, 198 insertions, 0 deletions
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);