Re: [PATCH 1/8] [watchdog] combine nmi_watchdog and softlockup

From: Frederic Weisbecker
Date: Wed May 12 2010 - 15:55:45 EST

On Fri, May 07, 2010 at 05:11:44PM -0400, Don Zickus wrote:
> The new nmi_watchdog (which uses the perf event subsystem) is very
> similar in structure to the softlockup detector. Using Ingo's suggestion,
> I combined the two functionalities into one file, kernel/watchdog.c.
>
> Now both the nmi_watchdog (or hardlockup detector) and softlockup detector
> sit on top of the perf event subsystem, which is run every 60 seconds or so
> to see if there are any lockups.
>
> To detect hardlockups, cpus not responding to interrupts, I implemented an
> hrtimer that runs 5 times for every perf event overflow event. If that stops
> counting on a cpu, then the cpu is most likely in trouble.
>
> To detect softlockups, tasks not yielding to the scheduler, I used the
> previous kthread idea that now gets kicked every time the hrtimer fires.
> If the kthread isn't being scheduled neither is anyone else and the
> warning is printed to the console.
>
> I tested this on x86_64 and both the softlockup and hardlockup paths work.
>
> V2:
> - cleaned up the Kconfig and softlockup combination
> - surrounded hardlockup cases with #ifdef CONFIG_PERF_EVENTS_NMI
> - seperated out the softlockup case from perf event subsystem
> - re-arranged the enabling/disabling nmi watchdog from proc space
> - added cpumasks for hardlockup failure cases
> - removed fallback to soft events if no PMU exists for hard events
>
> V3:
> - comment cleanups
> - drop support for older softlockup code
> - per_cpu cleanups
> - completely remove software clock base hardlockup detector
> - use per_cpu masking on hard/soft lockup detection
> - #ifdef cleanups
> - rename config option NMI_WATCHDOG to LOCKUP_DETECTOR
> - documentation additions
>
> V4:
> - documentation fixes
> - convert per_cpu to __get_cpu_var
> - powerpc compile fixes
>
> V5:
> - split apart warn flags for hard and soft lockups
>
> TODO:
> - figure out how to make an arch-agnostic clock2cycles call (if possible)
> to feed into perf events as a sample period
>
> Signed-off-by: Don Zickus <dzickus@xxxxxxxxxx>
> ---
> Documentation/kernel-parameters.txt | 2 +
> arch/x86/include/asm/nmi.h | 2 +-
> arch/x86/kernel/apic/Makefile | 4 +-
> arch/x86/kernel/apic/hw_nmi.c | 2 +-
> arch/x86/kernel/traps.c | 4 +-
> include/linux/nmi.h | 8 +-
> include/linux/sched.h | 6 +
> init/Kconfig | 5 +-
> kernel/Makefile | 3 +-
> kernel/sysctl.c | 21 +-
> kernel/watchdog.c | 577 +++++++++++++++++++++++++++++++++++
> lib/Kconfig.debug | 30 ++-
> 12 files changed, 635 insertions(+), 29 deletions(-)
> create mode 100644 kernel/watchdog.c
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 736d456..705f16f 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1764,6 +1764,8 @@ and is between 256 and 4096 characters. It is defined in the file
>
> nousb [USB] Disable the USB subsystem
>
> + nowatchdog [KNL] Disable the lockup detector.
> +
> nowb [ARM]
>
> nox2apic [X86-64,APIC] Do not enable x2APIC mode.
> diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
> index 5b41b0f..932f0f8 100644
> --- a/arch/x86/include/asm/nmi.h
> +++ b/arch/x86/include/asm/nmi.h
> @@ -17,7 +17,7 @@ int do_nmi_callback(struct pt_regs *regs, int cpu);
>
> extern void die_nmi(char *str, struct pt_regs *regs, int do_panic);
> extern int check_nmi_watchdog(void);
> -#if !defined(CONFIG_NMI_WATCHDOG)
> +#if !defined(CONFIG_LOCKUP_DETECTOR)
> extern int nmi_watchdog_enabled;
> #endif
> extern int avail_to_resrv_perfctr_nmi_bit(unsigned int);
> diff --git a/arch/x86/kernel/apic/Makefile b/arch/x86/kernel/apic/Makefile
> index 1a4512e..52f32e0 100644
> --- a/arch/x86/kernel/apic/Makefile
> +++ b/arch/x86/kernel/apic/Makefile
> @@ -3,10 +3,10 @@
> #
>
> obj-$(CONFIG_X86_LOCAL_APIC) += apic.o apic_noop.o probe_$(BITS).o ipi.o
> -ifneq ($(CONFIG_NMI_WATCHDOG),y)
> +ifneq ($(CONFIG_LOCKUP_DETECTOR),y)
> obj-$(CONFIG_X86_LOCAL_APIC) += nmi.o
> endif
> -obj-$(CONFIG_NMI_WATCHDOG) += hw_nmi.o
> +obj-$(CONFIG_LOCKUP_DETECTOR) += hw_nmi.o
>
> obj-$(CONFIG_X86_IO_APIC) += io_apic.o
> obj-$(CONFIG_SMP) += ipi.o
> diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
> index e8b78a0..79425f9 100644
> --- a/arch/x86/kernel/apic/hw_nmi.c
> +++ b/arch/x86/kernel/apic/hw_nmi.c
> @@ -89,7 +89,7 @@ int hw_nmi_is_cpu_stuck(struct pt_regs *regs)
>
> u64 hw_nmi_get_sample_period(void)
> {
> - return cpu_khz * 1000;
> + return (u64)(cpu_khz) * 1000 * 60;
> }
>
> #ifdef ARCH_HAS_NMI_WATCHDOG
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index bdc7fab..bd347c2 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -406,7 +406,7 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
> == NOTIFY_STOP)
> return;
>
> -#ifndef CONFIG_NMI_WATCHDOG
> +#ifndef CONFIG_LOCKUP_DETECTOR
> /*
> * Ok, so this is none of the documented NMI sources,
> * so it must be the NMI watchdog.
> @@ -414,7 +414,7 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
> if (nmi_watchdog_tick(regs, reason))
> return;
> if (!do_nmi_callback(regs, cpu))
> -#endif /* !CONFIG_NMI_WATCHDOG */
> +#endif /* !CONFIG_LOCKUP_DETECTOR */
> unknown_nmi_error(reason, regs);
> #else
> unknown_nmi_error(reason, regs);
> diff --git a/include/linux/nmi.h b/include/linux/nmi.h
> index 22cc796..abd48aa 100644
> --- a/include/linux/nmi.h
> +++ b/include/linux/nmi.h
> @@ -20,7 +20,7 @@ extern void touch_nmi_watchdog(void);
> extern void acpi_nmi_disable(void);
> extern void acpi_nmi_enable(void);
> #else
> -#ifndef CONFIG_NMI_WATCHDOG
> +#ifndef CONFIG_LOCKUP_DETECTOR
> static inline void touch_nmi_watchdog(void)
> {
> touch_softlockup_watchdog();
> @@ -51,12 +51,12 @@ static inline bool trigger_all_cpu_backtrace(void)
> }
> #endif
>
> -#ifdef CONFIG_NMI_WATCHDOG
> +#ifdef CONFIG_LOCKUP_DETECTOR
> int hw_nmi_is_cpu_stuck(struct pt_regs *);
> u64 hw_nmi_get_sample_period(void);
> -extern int nmi_watchdog_enabled;
> +extern int watchdog_enabled;
> struct ctl_table;
> -extern int proc_nmi_enabled(struct ctl_table *, int ,
> +extern int proc_dowatchdog_enabled(struct ctl_table *, int ,
> void __user *, size_t *, loff_t *);
> #endif
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 6f7bba9..2455ff5 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -338,6 +338,12 @@ extern int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
> size_t *lenp, loff_t *ppos);
> #endif
>
> +#ifdef CONFIG_LOCKUP_DETECTOR
> +extern int proc_dowatchdog_thresh(struct ctl_table *table, int write,
> + void __user *buffer,
> + size_t *lenp, loff_t *ppos);
> +#endif
> +
> /* Attach to any functions which should be ignored in wchan output. */
> #define __sched __attribute__((__section__(".sched.text")))
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 7331a16..c5ce8b7 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -948,8 +948,11 @@ config PERF_USE_VMALLOC
>
> config PERF_EVENTS_NMI
> bool
> + depends on PERF_EVENTS
> help
> - Arch has support for nmi_watchdog
> + System hardware can generate an NMI using the perf event
> + subsystem. Also has support for calculating CPU cycle events
> + to determine how many clock cycles in a given period.
>
> menu "Kernel Performance Events And Counters"
>
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 8a5abe5..cc3acb3 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -75,9 +75,8 @@ obj-$(CONFIG_GCOV_KERNEL) += gcov/
> obj-$(CONFIG_AUDIT_TREE) += audit_tree.o
> obj-$(CONFIG_KPROBES) += kprobes.o
> obj-$(CONFIG_KGDB) += kgdb.o
> -obj-$(CONFIG_DETECT_SOFTLOCKUP) += softlockup.o
> -obj-$(CONFIG_NMI_WATCHDOG) += nmi_watchdog.o
> obj-$(CONFIG_DETECT_HUNG_TASK) += hung_task.o
> +obj-$(CONFIG_LOCKUP_DETECTOR) += watchdog.o
> obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
> obj-$(CONFIG_SECCOMP) += seccomp.o
> obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index ac72c9e..1083897 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -60,7 +60,7 @@
> #include <asm/io.h>
> #endif
>
> -#ifdef CONFIG_NMI_WATCHDOG
> +#ifdef CONFIG_LOCKUP_DETECTOR
> #include <linux/nmi.h>
> #endif
>
> @@ -696,16 +696,25 @@ static struct ctl_table kern_table[] = {
> .mode = 0444,
> .proc_handler = proc_dointvec,
> },
> -#if defined(CONFIG_NMI_WATCHDOG)
> +#if defined(CONFIG_LOCKUP_DETECTOR)
> {
> - .procname = "nmi_watchdog",
> - .data = &nmi_watchdog_enabled,
> + .procname = "watchdog",
> + .data = &watchdog_enabled,



I suspect this could break some userspace apps that rely on
this sysctl option.

May be you should keep the nmi_watchdog around and schedule its
removal for later in the feature_removal_schedule.txt file.



> .maxlen = sizeof (int),
> .mode = 0644,
> - .proc_handler = proc_nmi_enabled,
> + .proc_handler = proc_dowatchdog_enabled,
> + },
> + {
> + .procname = "watchdog_thresh",
> + .data = &softlockup_thresh,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dowatchdog_thresh,
> + .extra1 = &neg_one,
> + .extra2 = &sixty,
> },
> #endif
> -#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86) && !defined(CONFIG_NMI_WATCHDOG)
> +#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86) && !defined(CONFIG_LOCKUP_DETECTOR)
> {
> .procname = "unknown_nmi_panic",
> .data = &unknown_nmi_panic,
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> new file mode 100644
> index 0000000..2684e95
> --- /dev/null
> +++ b/kernel/watchdog.c
> @@ -0,0 +1,577 @@
> +/*
> + * Detect hard and soft lockups on a system
> + *
> + * 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/kthread.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>
> +
> +int watchdog_enabled;
> +int __read_mostly softlockup_thresh = 60;
> +
> +static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
> +static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
> +static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
> +static DEFINE_PER_CPU(bool, hard_watchdog_warn);


This one should be under CONFIG_PERF_EVENTS_NMI


> +static DEFINE_PER_CPU(bool, soft_watchdog_warn);
> +#ifdef CONFIG_PERF_EVENTS_NMI
> +static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
> +static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
> +static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
> +#endif
> +
> +static int __read_mostly did_panic;
> +static int __initdata no_watchdog;
> +
> +
> +/* boot commands */
> +/*
> + * Should we panic when a soft-lockup or hard-lockup occurs:
> + */
> +#ifdef CONFIG_PERF_EVENTS_NMI
> +static int hardlockup_panic;
> +
> +static int __init hardlockup_panic_setup(char *str)
> +{
> + if (!strncmp(str, "panic", 5))
> + hardlockup_panic = 1;
> + return 1;
> +}
> +__setup("nmi_watchdog=", hardlockup_panic_setup);



If nmi_watchdog=0, this won't deactivate anymore the hardlockup
detector.



> +#endif
> +
> +unsigned int __read_mostly softlockup_panic =
> + CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
> +
> +static int __init softlockup_panic_setup(char *str)
> +{
> + softlockup_panic = simple_strtoul(str, NULL, 0);
> +
> + return 1;
> +}
> +__setup("softlockup_panic=", softlockup_panic_setup);
> +
> +static int __init nowatchdog_setup(char *str)
> +{
> + no_watchdog = 1;
> + return 1;
> +}
> +__setup("nowatchdog", nowatchdog_setup);
> +
> +/* deprecated */
> +static int __init nosoftlockup_setup(char *str)
> +{
> + no_watchdog = 1;
> + return 1;
> +}
> +__setup("nosoftlockup", nosoftlockup_setup);
> +/* */
> +
> +
> +/*
> + * 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(int this_cpu)
> +{
> + return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
> +}
> +
> +static unsigned long get_sample_period(void)
> +{
> + /*
> + * convert softlockup_thresh from seconds to ns
> + * the divide by 5 is to give hrtimer 5 chances to
> + * increment before the hardlockup detector generates
> + * a warning
> + */
> + return softlockup_thresh / 5 * NSEC_PER_SEC;
> +}
> +
> +/* Commands for resetting the watchdog */
> +static void __touch_watchdog(void)
> +{
> + int this_cpu = raw_smp_processor_id();


This must use smp_processor_id() for preemption disabled
checks.



> +
> + __get_cpu_var(watchdog_touch_ts) = get_timestamp(this_cpu);
> +}
> +
> +void touch_watchdog(void)
> +{
> + __get_cpu_var(watchdog_touch_ts) = 0;
> +}
> +EXPORT_SYMBOL(touch_watchdog);
> +
> +void touch_all_watchdog(void)
> +{
> + int cpu;
> +
> + /*
> + * this is done lockless
> + * do we care if a 0 races with a timestamp?
> + * all it means is the softlock check starts one cycle later
> + */
> + for_each_online_cpu(cpu)
> + per_cpu(watchdog_touch_ts, cpu) = 0;
> +}
> +
> +void touch_nmi_watchdog(void)
> +{
> + touch_watchdog();
> +}
> +EXPORT_SYMBOL(touch_nmi_watchdog);
> +
> +void touch_all_nmi_watchdog(void)
> +{
> + touch_all_watchdog();
> +}
> +
> +void touch_softlockup_watchdog(void)
> +{
> + touch_watchdog();
> +}
> +
> +void touch_all_softlockup_watchdogs(void)
> +{
> + touch_all_watchdog();
> +}
> +
> +void softlockup_tick(void)
> +{
> +}
> +
> +#ifdef CONFIG_PERF_EVENTS_NMI
> +/* watchdog detector functions */
> +static int is_hardlockup(int cpu)
> +{
> + unsigned long hrint = per_cpu(hrtimer_interrupts, cpu);
> +
> + if (per_cpu(hrtimer_interrupts_saved, cpu) == hrint)
> + return 1;
> +
> + per_cpu(hrtimer_interrupts_saved, cpu) = hrint;



All these per_cpu() should be __this_cpu_var() for readability,
for the preemption disabled safety check, and may be even
for optimization reasons: if an arch defines its own __my_cpu_offset,
it may get it faster.




> +static int is_softlockup(unsigned long touch_ts, int cpu)
> +{
> + unsigned long now = get_timestamp(cpu);
> +
> + /* Warn about unreasonable delays: */
> + if (now > (touch_ts + softlockup_thresh))
> + return now - touch_ts;
> +
> + return 0;
> +}
> +
> +static int
> +watchdog_panic(struct notifier_block *this, unsigned long event, void *ptr)
> +{
> + did_panic = 1;
> +
> + return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block panic_block = {
> + .notifier_call = watchdog_panic,
> +};
> +
> +#ifdef CONFIG_PERF_EVENTS_NMI
> +static struct perf_event_attr wd_hw_attr = {
> + .type = PERF_TYPE_HARDWARE,
> + .config = PERF_COUNT_HW_CPU_CYCLES,
> + .size = sizeof(struct perf_event_attr),
> + .pinned = 1,
> + .disabled = 1,
> +};
> +
> +/* Callback function for perf event subsystem */
> +void watchdog_overflow_callback(struct perf_event *event, int nmi,
> + struct perf_sample_data *data,
> + struct pt_regs *regs)
> +{
> + int this_cpu = smp_processor_id();
> + unsigned long touch_ts = per_cpu(watchdog_touch_ts, this_cpu);


same here



> +
> + if (touch_ts == 0) {
> + __touch_watchdog();
> + return;
> + }
> +
> + /* check for a hardlockup
> + * This is done by making sure our timer interrupt
> + * is incrementing. The timer interrupt should have
> + * fired multiple times before we overflow'd. If it hasn't
> + * then this is a good indication the cpu is stuck
> + */
> + if (is_hardlockup(this_cpu)) {
> + /* only print hardlockups once */
> + if (__get_cpu_var(hard_watchdog_warn) == true)
> + return;
> +
> + if (hardlockup_panic)
> + panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
> + else
> + WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
> +
> + __get_cpu_var(hard_watchdog_warn) = true;
> + return;
> + }
> +
> + __get_cpu_var(hard_watchdog_warn) = false;
> + return;
> +}
> +static void watchdog_interrupt_count(void)
> +{
> + __get_cpu_var(hrtimer_interrupts)++;
> +}
> +#else
> +static inline void watchdog_interrupt_count(void) { return; }
> +#endif /* CONFIG_PERF_EVENTS_NMI */
> +
> +/* watchdog kicker functions */
> +static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
> +{
> + int this_cpu = smp_processor_id();
> + unsigned long touch_ts = __get_cpu_var(watchdog_touch_ts);
> + struct pt_regs *regs = get_irq_regs();
> + int duration;
> +
> + /* kick the hardlockup detector */
> + watchdog_interrupt_count();
> +
> + /* kick the softlockup detector */
> + wake_up_process(__get_cpu_var(softlockup_watchdog));
> +
> + /* .. and repeat */
> + hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
> +
> + if (touch_ts == 0) {
> + __touch_watchdog();
> + return HRTIMER_RESTART;
> + }
> +
> + /* check for a softlockup
> + * This is done by making sure a high priority task is
> + * being scheduled. The task touches the watchdog to
> + * indicate it is getting cpu time. If it hasn't then
> + * this is a good indication some task is hogging the cpu
> + */
> + duration = is_softlockup(touch_ts, this_cpu);
> + if (unlikely(duration)) {
> + /* only warn once */
> + if (__get_cpu_var(soft_watchdog_warn) == true)
> + return HRTIMER_RESTART;
> +
> + printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
> + this_cpu, duration,
> + current->comm, task_pid_nr(current));
> + print_modules();
> + print_irqtrace_events(current);
> + if (regs)
> + show_regs(regs);
> + else
> + dump_stack();
> +
> + if (softlockup_panic)
> + panic("softlockup: hung tasks");
> + __get_cpu_var(soft_watchdog_warn) = true;
> + } else
> + __get_cpu_var(soft_watchdog_warn) = false;
> +
> + return HRTIMER_RESTART;
> +}
> +
> +
> +/*
> + * The watchdog thread - touches the timestamp.
> + */
> +static int watchdog(void *__bind_cpu)
> +{
> + struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
> + struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, (unsigned long)__bind_cpu);


This is bound to a single cpu already: __raw_get_cpu_var() (because we don't
need the preempt disabled check here).

Thanks.

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