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>
This commit is contained in:
Don Zickus
Ingo Molnar
parent
e40b17208b
commit
1fb9d6ad27
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/*
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* HW NMI watchdog support
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*
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* started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
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*
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* Arch specific calls to support NMI watchdog
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*
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* Bits copied from original nmi.c file
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*
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*/
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#include <asm/apic.h>
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#include <linux/smp.h>
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#include <linux/cpumask.h>
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#include <linux/sched.h>
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#include <linux/percpu.h>
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#include <linux/cpumask.h>
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#include <linux/kernel_stat.h>
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#include <asm/mce.h>
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#include <linux/nmi.h>
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#include <linux/module.h>
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/* For reliability, we're prepared to waste bits here. */
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static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
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static DEFINE_PER_CPU(unsigned, last_irq_sum);
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/*
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* Take the local apic timer and PIT/HPET into account. We don't
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* know which one is active, when we have highres/dyntick on
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*/
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static inline unsigned int get_timer_irqs(int cpu)
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{
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return per_cpu(irq_stat, cpu).apic_timer_irqs +
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per_cpu(irq_stat, cpu).irq0_irqs;
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}
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static inline int mce_in_progress(void)
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{
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#if defined(CONFIG_X86_MCE)
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return atomic_read(&mce_entry) > 0;
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#endif
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return 0;
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}
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int hw_nmi_is_cpu_stuck(struct pt_regs *regs)
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{
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unsigned int sum;
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int cpu = smp_processor_id();
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/* FIXME: cheap hack for this check, probably should get its own
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* die_notifier handler
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*/
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if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
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static DEFINE_SPINLOCK(lock); /* Serialise the printks */
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spin_lock(&lock);
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printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu);
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show_regs(regs);
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dump_stack();
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spin_unlock(&lock);
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cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
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}
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/* if we are doing an mce, just assume the cpu is not stuck */
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/* Could check oops_in_progress here too, but it's safer not to */
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if (mce_in_progress())
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return 0;
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/* We determine if the cpu is stuck by checking whether any
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* interrupts have happened since we last checked. Of course
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* an nmi storm could create false positives, but the higher
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* level logic should account for that
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*/
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sum = get_timer_irqs(cpu);
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if (__get_cpu_var(last_irq_sum) == sum) {
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return 1;
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} else {
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__get_cpu_var(last_irq_sum) = sum;
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return 0;
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}
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}
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void arch_trigger_all_cpu_backtrace(void)
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{
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int i;
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cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
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printk(KERN_INFO "sending NMI to all CPUs:\n");
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apic->send_IPI_all(NMI_VECTOR);
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/* Wait for up to 10 seconds for all CPUs to do the backtrace */
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for (i = 0; i < 10 * 1000; i++) {
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if (cpumask_empty(to_cpumask(backtrace_mask)))
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break;
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mdelay(1);
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}
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}
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/* STUB calls to mimic old nmi_watchdog behaviour */
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unsigned int nmi_watchdog = NMI_NONE;
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EXPORT_SYMBOL(nmi_watchdog);
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atomic_t nmi_active = ATOMIC_INIT(0); /* oprofile uses this */
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EXPORT_SYMBOL(nmi_active);
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int nmi_watchdog_enabled;
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int unknown_nmi_panic;
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void cpu_nmi_set_wd_enabled(void) { return; }
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void acpi_nmi_enable(void) { return; }
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void acpi_nmi_disable(void) { return; }
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void stop_apic_nmi_watchdog(void *unused) { return; }
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void setup_apic_nmi_watchdog(void *unused) { return; }
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int __init check_nmi_watchdog(void) { return 0; }
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@ -0,0 +1,191 @@
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/*
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* Detect Hard Lockups using the NMI
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*
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* started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
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*
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* this code detects hard lockups: incidents in where on a CPU
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* the kernel does not respond to anything except NMI.
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*
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* Note: Most of this code is borrowed heavily from softlockup.c,
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* so thanks to Ingo for the initial implementation.
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* Some chunks also taken from arch/x86/kernel/apic/nmi.c, thanks
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* to those contributors as well.
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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/lockdep.h>
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#include <linux/notifier.h>
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#include <linux/module.h>
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#include <linux/sysctl.h>
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#include <asm/irq_regs.h>
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#include <linux/perf_event.h>
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static DEFINE_PER_CPU(struct perf_event *, nmi_watchdog_ev);
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static DEFINE_PER_CPU(int, nmi_watchdog_touch);
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static DEFINE_PER_CPU(long, alert_counter);
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void touch_nmi_watchdog(void)
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{
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__raw_get_cpu_var(nmi_watchdog_touch) = 1;
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touch_softlockup_watchdog();
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}
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EXPORT_SYMBOL(touch_nmi_watchdog);
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void touch_all_nmi_watchdog(void)
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{
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int cpu;
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for_each_online_cpu(cpu)
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per_cpu(nmi_watchdog_touch, cpu) = 1;
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touch_softlockup_watchdog();
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}
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#ifdef CONFIG_SYSCTL
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/*
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* proc handler for /proc/sys/kernel/nmi_watchdog
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*/
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int proc_nmi_enabled(struct ctl_table *table, int write,
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void __user *buffer, size_t *length, loff_t *ppos)
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{
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int cpu;
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if (per_cpu(nmi_watchdog_ev, smp_processor_id()) == NULL)
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nmi_watchdog_enabled = 0;
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else
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nmi_watchdog_enabled = 1;
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touch_all_nmi_watchdog();
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proc_dointvec(table, write, buffer, length, ppos);
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if (nmi_watchdog_enabled)
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for_each_online_cpu(cpu)
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perf_event_enable(per_cpu(nmi_watchdog_ev, cpu));
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else
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for_each_online_cpu(cpu)
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perf_event_disable(per_cpu(nmi_watchdog_ev, cpu));
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return 0;
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}
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#endif /* CONFIG_SYSCTL */
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struct perf_event_attr wd_attr = {
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.type = PERF_TYPE_HARDWARE,
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.config = PERF_COUNT_HW_CPU_CYCLES,
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.size = sizeof(struct perf_event_attr),
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.pinned = 1,
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.disabled = 1,
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};
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static int panic_on_timeout;
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void wd_overflow(struct perf_event *event, int nmi,
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struct perf_sample_data *data,
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struct pt_regs *regs)
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{
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int cpu = smp_processor_id();
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int touched = 0;
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if (__get_cpu_var(nmi_watchdog_touch)) {
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per_cpu(nmi_watchdog_touch, cpu) = 0;
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touched = 1;
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}
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/* check to see if the cpu is doing anything */
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if (!touched && hw_nmi_is_cpu_stuck(regs)) {
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/*
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* Ayiee, looks like this CPU is stuck ...
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* wait a few IRQs (5 seconds) before doing the oops ...
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*/
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per_cpu(alert_counter,cpu) += 1;
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if (per_cpu(alert_counter,cpu) == 5) {
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/*
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* die_nmi will return ONLY if NOTIFY_STOP happens..
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*/
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die_nmi("BUG: NMI Watchdog detected LOCKUP",
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regs, panic_on_timeout);
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}
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} else {
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per_cpu(alert_counter,cpu) = 0;
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}
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return;
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}
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/*
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* Create/destroy watchdog threads as CPUs come and go:
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*/
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static int __cpuinit
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cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
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{
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int hotcpu = (unsigned long)hcpu;
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struct perf_event *event;
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switch (action) {
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case CPU_UP_PREPARE:
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case CPU_UP_PREPARE_FROZEN:
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per_cpu(nmi_watchdog_touch, hotcpu) = 0;
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break;
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case CPU_ONLINE:
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case CPU_ONLINE_FROZEN:
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/* originally wanted the below chunk to be in CPU_UP_PREPARE, but caps is unpriv for non-CPU0 */
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wd_attr.sample_period = cpu_khz * 1000;
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event = perf_event_create_kernel_counter(&wd_attr, hotcpu, -1, wd_overflow);
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if (IS_ERR(event)) {
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printk(KERN_ERR "nmi watchdog failed to create perf event on %i: %p\n", hotcpu, event);
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return NOTIFY_BAD;
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}
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per_cpu(nmi_watchdog_ev, hotcpu) = event;
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perf_event_enable(per_cpu(nmi_watchdog_ev, hotcpu));
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break;
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#ifdef CONFIG_HOTPLUG_CPU
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case CPU_UP_CANCELED:
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case CPU_UP_CANCELED_FROZEN:
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perf_event_disable(per_cpu(nmi_watchdog_ev, hotcpu));
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case CPU_DEAD:
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case CPU_DEAD_FROZEN:
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event = per_cpu(nmi_watchdog_ev, hotcpu);
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per_cpu(nmi_watchdog_ev, hotcpu) = NULL;
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perf_event_release_kernel(event);
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break;
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#endif /* CONFIG_HOTPLUG_CPU */
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}
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return NOTIFY_OK;
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}
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static struct notifier_block __cpuinitdata cpu_nfb = {
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.notifier_call = cpu_callback
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};
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static int __initdata nonmi_watchdog;
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static int __init nonmi_watchdog_setup(char *str)
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{
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nonmi_watchdog = 1;
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return 1;
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}
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__setup("nonmi_watchdog", nonmi_watchdog_setup);
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static int __init spawn_nmi_watchdog_task(void)
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{
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void *cpu = (void *)(long)smp_processor_id();
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int err;
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if (nonmi_watchdog)
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return 0;
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err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
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if (err == NOTIFY_BAD) {
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BUG();
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return 1;
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}
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cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
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register_cpu_notifier(&cpu_nfb);
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return 0;
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}
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early_initcall(spawn_nmi_watchdog_task);
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