nmi_watchdog: Add new, generic implementation, using perf events

This is a new generic nmi_watchdog implementation using the perf
events infrastructure as suggested by Ingo.

The implementation is simple, just create an in-kernel perf
event and register an overflow handler to check for cpu lockups.

I created a generic implementation that lives in kernel/ and
the hardware specific part that for now lives in arch/x86.

This approach has a number of advantages:

 - It simplifies the x86 PMU implementation in the long run,
   in that it removes the hardcoded low-level PMU implementation
   that was the NMI watchdog before.

 - It allows new NMI watchdog features to be added in a central
   place.

 - It allows other architectures to enable the NMI watchdog,
   as long as they have perf events (that provide NMIs)
   implemented.

 - It also allows for more graceful co-existence of existing
   perf events apps and the NMI watchdog - before these changes
   the relationship was exclusive. (The NMI watchdog will 'spend'
   a perf event when enabled. In later iterations we might be
   able to piggyback from an existing NMI event without having
   to allocate a hardware event for the NMI watchdog - turning
   this into a no-hardware-cost feature.)

As for compatibility, we'll keep the old NMI watchdog code as
well until the new one can 100% replace it on all CPUs, old and
new alike.  That might take some time as the NMI watchdog has
been ported to many CPU models.

I have done light testing to make sure the framework works
correctly and it does.

 v2: Set the correct timeout values based on the old nmi
     watchdog

Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: gorcunov@gmail.com
Cc: aris@redhat.com
Cc: peterz@infradead.org
LKML-Reference: <1265424425-31562-3-git-send-email-dzickus@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 191 insertions, 0 deletions

diff --git a/kernel/nmi_watchdog.c b/kernel/nmi_watchdog.c
new file mode 100644
index 00000000000..36817b214d6
--- /dev/null
+++ b/kernel/nmi_watchdog.c
@@ -0,0 +1,191 @@
+/*
+ * Detect Hard Lockups using the NMI
+ *
+ * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
+ *
+ * this code detects hard lockups: incidents in where on a CPU
+ * the kernel does not respond to anything except NMI.
+ *
+ * Note: Most of this code is borrowed heavily from softlockup.c,
+ * so thanks to Ingo for the initial implementation.
+ * Some chunks also taken from arch/x86/kernel/apic/nmi.c, thanks
+ * to those contributors as well.
+ */
+
+#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/lockdep.h>
+#include <linux/notifier.h>
+#include <linux/module.h>
+#include <linux/sysctl.h>
+
+#include <asm/irq_regs.h>
+#include <linux/perf_event.h>
+
+static DEFINE_PER_CPU(struct perf_event *, nmi_watchdog_ev);
+static DEFINE_PER_CPU(int, nmi_watchdog_touch);
+static DEFINE_PER_CPU(long, alert_counter);
+
+void touch_nmi_watchdog(void)
+{
+	__raw_get_cpu_var(nmi_watchdog_touch) = 1;
+	touch_softlockup_watchdog();
+}
+EXPORT_SYMBOL(touch_nmi_watchdog);
+
+void touch_all_nmi_watchdog(void)
+{
+	int cpu;
+
+	for_each_online_cpu(cpu)
+		per_cpu(nmi_watchdog_touch, cpu) = 1;
+	touch_softlockup_watchdog();
+}
+
+#ifdef CONFIG_SYSCTL
+/*
+ * proc handler for /proc/sys/kernel/nmi_watchdog
+ */
+int proc_nmi_enabled(struct ctl_table *table, int write,
+		     void __user *buffer, size_t *length, loff_t *ppos)
+{
+	int cpu;
+
+	if (per_cpu(nmi_watchdog_ev, smp_processor_id()) == NULL)
+		nmi_watchdog_enabled = 0;
+	else
+		nmi_watchdog_enabled = 1;
+
+	touch_all_nmi_watchdog();
+	proc_dointvec(table, write, buffer, length, ppos);
+	if (nmi_watchdog_enabled)
+		for_each_online_cpu(cpu)
+			perf_event_enable(per_cpu(nmi_watchdog_ev, cpu));
+	else
+		for_each_online_cpu(cpu)
+			perf_event_disable(per_cpu(nmi_watchdog_ev, cpu));
+	return 0;
+}
+
+#endif /* CONFIG_SYSCTL */
+
+struct perf_event_attr wd_attr = {
+	.type = PERF_TYPE_HARDWARE,
+	.config = PERF_COUNT_HW_CPU_CYCLES,
+	.size = sizeof(struct perf_event_attr),
+	.pinned = 1,
+	.disabled = 1,
+};
+
+static int panic_on_timeout;
+
+void wd_overflow(struct perf_event *event, int nmi,
+		 struct perf_sample_data *data,
+		 struct pt_regs *regs)
+{
+	int cpu = smp_processor_id();
+	int touched = 0;
+
+	if (__get_cpu_var(nmi_watchdog_touch)) {
+		per_cpu(nmi_watchdog_touch, cpu) = 0;
+		touched = 1;
+	}
+
+	/* check to see if the cpu is doing anything */
+	if (!touched && hw_nmi_is_cpu_stuck(regs)) {
+		/*
+		 * Ayiee, looks like this CPU is stuck ...
+		 * wait a few IRQs (5 seconds) before doing the oops ...
+		 */
+		per_cpu(alert_counter,cpu) += 1;
+		if (per_cpu(alert_counter,cpu) == 5) {
+			/*
+			 * die_nmi will return ONLY if NOTIFY_STOP happens..
+			 */
+			die_nmi("BUG: NMI Watchdog detected LOCKUP",
+				regs, panic_on_timeout);
+		}
+	} else {
+		per_cpu(alert_counter,cpu) = 0;
+	}
+
+	return;
+}
+
+/*
+ * Create/destroy watchdog threads as CPUs come and go:
+ */
+static int __cpuinit
+cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
+{
+	int hotcpu = (unsigned long)hcpu;
+	struct perf_event *event;
+
+	switch (action) {
+	case CPU_UP_PREPARE:
+	case CPU_UP_PREPARE_FROZEN:
+		per_cpu(nmi_watchdog_touch, hotcpu) = 0;
+		break;
+	case CPU_ONLINE:
+	case CPU_ONLINE_FROZEN:
+		/* originally wanted the below chunk to be in CPU_UP_PREPARE, but caps is unpriv for non-CPU0 */
+		wd_attr.sample_period = cpu_khz * 1000;
+		event = perf_event_create_kernel_counter(&wd_attr, hotcpu, -1, wd_overflow);
+		if (IS_ERR(event)) {
+			printk(KERN_ERR "nmi watchdog failed to create perf event on %i: %p\n", hotcpu, event);
+			return NOTIFY_BAD;
+		}
+		per_cpu(nmi_watchdog_ev, hotcpu) = event;
+		perf_event_enable(per_cpu(nmi_watchdog_ev, hotcpu));
+		break;
+#ifdef CONFIG_HOTPLUG_CPU
+	case CPU_UP_CANCELED:
+	case CPU_UP_CANCELED_FROZEN:
+		perf_event_disable(per_cpu(nmi_watchdog_ev, hotcpu));
+	case CPU_DEAD:
+	case CPU_DEAD_FROZEN:
+		event = per_cpu(nmi_watchdog_ev, hotcpu);
+		per_cpu(nmi_watchdog_ev, hotcpu) = NULL;
+		perf_event_release_kernel(event);
+		break;
+#endif /* CONFIG_HOTPLUG_CPU */
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata cpu_nfb = {
+	.notifier_call = cpu_callback
+};
+
+static int __initdata nonmi_watchdog;
+
+static int __init nonmi_watchdog_setup(char *str)
+{
+	nonmi_watchdog = 1;
+	return 1;
+}
+__setup("nonmi_watchdog", nonmi_watchdog_setup);
+
+static int __init spawn_nmi_watchdog_task(void)
+{
+	void *cpu = (void *)(long)smp_processor_id();
+	int err;
+
+	if (nonmi_watchdog)
+		return 0;
+
+	err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
+	if (err == NOTIFY_BAD) {
+		BUG();
+		return 1;
+	}
+	cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
+	register_cpu_notifier(&cpu_nfb);
+
+	return 0;
+}
+early_initcall(spawn_nmi_watchdog_task);