[PATCH] detect soft lockups

This patch adds a new kernel debug feature: CONFIG_DETECT_SOFTLOCKUP.

When enabled then per-CPU watchdog threads are started, which try to run
once per second.  If they get delayed for more than 10 seconds then a
callback from the timer interrupt detects this condition and prints out a
warning message and a stack dump (once per lockup incident).  The feature
is otherwise non-intrusive, it doesnt try to unlock the box in any way, it
only gets the debug info out, automatically, and on all CPUs affected by
the lockup.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-Off-By: Matthias Urlichs <smurf@smurf.noris.de>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/Makefile

@@ -27,6 +27,7 @@ obj-$(CONFIG_AUDIT) += audit.o
 obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
 obj-$(CONFIG_KPROBES) += kprobes.o
 obj-$(CONFIG_SYSFS) += ksysfs.o
+obj-$(CONFIG_DETECT_SOFTLOCKUP) += softlockup.o
 obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
 obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
 obj-$(CONFIG_SECCOMP) += seccomp.o

kernel/power/swsusp.c

@@ -1059,6 +1059,7 @@ int swsusp_resume(void)
 	BUG_ON(!error);
 	restore_processor_state();
 	restore_highmem();
+	touch_softlockup_watchdog();
 	device_power_up();
 	local_irq_enable();
 	return error;

kernel/softlockup.c

@@ -0,0 +1,151 @@
+/*
+ * Detect Soft Lockups
+ *
+ * started by Ingo Molnar, (C) 2005, Red Hat
+ *
+ * this code detects soft lockups: incidents in where on a CPU
+ * the kernel does not reschedule for 10 seconds or more.
+ */
+
+#include <linux/mm.h>
+#include <linux/cpu.h>
+#include <linux/init.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/notifier.h>
+#include <linux/module.h>
+
+static DEFINE_SPINLOCK(print_lock);
+
+static DEFINE_PER_CPU(unsigned long, timestamp) = 0;
+static DEFINE_PER_CPU(unsigned long, print_timestamp) = 0;
+static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
+
+static int did_panic = 0;
+static int softlock_panic(struct notifier_block *this, unsigned long event,
+				void *ptr)
+{
+	did_panic = 1;
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block panic_block = {
+	.notifier_call = softlock_panic,
+};
+
+void touch_softlockup_watchdog(void)
+{
+	per_cpu(timestamp, raw_smp_processor_id()) = jiffies;
+}
+EXPORT_SYMBOL(touch_softlockup_watchdog);
+
+/*
+ * This callback runs from the timer interrupt, and checks
+ * whether the watchdog thread has hung or not:
+ */
+void softlockup_tick(struct pt_regs *regs)
+{
+	int this_cpu = smp_processor_id();
+	unsigned long timestamp = per_cpu(timestamp, this_cpu);
+
+	if (per_cpu(print_timestamp, this_cpu) == timestamp)
+		return;
+
+	/* Do not cause a second panic when there already was one */
+	if (did_panic)
+		return;
+
+	if (time_after(jiffies, timestamp + 10*HZ)) {
+		per_cpu(print_timestamp, this_cpu) = timestamp;
+
+		spin_lock(&print_lock);
+		printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n",
+			this_cpu);
+		show_regs(regs);
+		spin_unlock(&print_lock);
+	}
+}
+
+/*
+ * The watchdog thread - runs every second and touches the timestamp.
+ */
+static int watchdog(void * __bind_cpu)
+{
+	struct sched_param param = { .sched_priority = 99 };
+	int this_cpu = (long) __bind_cpu;
+
+	printk("softlockup thread %d started up.\n", this_cpu);
+
+	sched_setscheduler(current, SCHED_FIFO, &param);
+	current->flags |= PF_NOFREEZE;
+
+	set_current_state(TASK_INTERRUPTIBLE);
+
+	/*
+	 * Run briefly once per second - if this gets delayed for
+	 * more than 10 seconds then the debug-printout triggers
+	 * in softlockup_tick():
+	 */
+	while (!kthread_should_stop()) {
+		msleep_interruptible(1000);
+		touch_softlockup_watchdog();
+	}
+	__set_current_state(TASK_RUNNING);
+
+	return 0;
+}
+
+/*
+ * Create/destroy watchdog threads as CPUs come and go:
+ */
+static int __devinit
+cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
+{
+	int hotcpu = (unsigned long)hcpu;
+	struct task_struct *p;
+
+	switch (action) {
+	case CPU_UP_PREPARE:
+		BUG_ON(per_cpu(watchdog_task, hotcpu));
+		p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
+		if (IS_ERR(p)) {
+			printk("watchdog for %i failed\n", hotcpu);
+			return NOTIFY_BAD;
+		}
+  		per_cpu(watchdog_task, hotcpu) = p;
+		kthread_bind(p, hotcpu);
+ 		break;
+	case CPU_ONLINE:
+
+		wake_up_process(per_cpu(watchdog_task, hotcpu));
+		break;
+#ifdef CONFIG_HOTPLUG_CPU
+	case CPU_UP_CANCELED:
+		/* Unbind so it can run.  Fall thru. */
+		kthread_bind(per_cpu(watchdog_task, hotcpu), smp_processor_id());
+	case CPU_DEAD:
+		p = per_cpu(watchdog_task, hotcpu);
+		per_cpu(watchdog_task, hotcpu) = NULL;
+		kthread_stop(p);
+		break;
+#endif /* CONFIG_HOTPLUG_CPU */
+ 	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block __devinitdata cpu_nfb = {
+	.notifier_call = cpu_callback
+};
+
+__init void spawn_softlockup_task(void)
+{
+	void *cpu = (void *)(long)smp_processor_id();
+
+	cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
+	cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
+	register_cpu_notifier(&cpu_nfb);
+
+	notifier_chain_register(&panic_notifier_list, &panic_block);
+}
+

kernel/timer.c

@@ -950,6 +950,7 @@ void do_timer(struct pt_regs *regs)
 {
 	jiffies_64++;
 	update_times();
+	softlockup_tick(regs);
 }
 
 #ifdef __ARCH_WANT_SYS_ALARM