kernel-ark/kernel/watchdog.c
Sameer Nanda 45226e944c NMI watchdog: fix for lockup detector breakage on resume
On the suspend/resume path the boot CPU does not go though an
offline->online transition.  This breaks the NMI detector post-resume
since it depends on PMU state that is lost when the system gets
suspended.

Fix this by forcing a CPU offline->online transition for the lockup
detector on the boot CPU during resume.

To provide more context, we enable NMI watchdog on Chrome OS.  We have
seen several reports of systems freezing up completely which indicated
that the NMI watchdog was not firing for some reason.

Debugging further, we found a simple way of repro'ing system freezes --
issuing the command 'tasket 1 sh -c "echo nmilockup > /proc/breakme"'
after the system has been suspended/resumed one or more times.

With this patch in place, the system freeze result in panics, as
expected.

These panics provide a nice stack trace for us to debug the actual issue
causing the freeze.

[akpm@linux-foundation.org: fiddle with code comment]
[akpm@linux-foundation.org: make lockup_detector_bootcpu_resume() conditional on CONFIG_SUSPEND]
[akpm@linux-foundation.org: fix section errors]
Signed-off-by: Sameer Nanda <snanda@chromium.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Mandeep Singh Baines <msb@chromium.org>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-07-30 17:25:13 -07:00

647 lines
16 KiB
C

/*
* Detect hard and soft lockups on a system
*
* started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
*
* Note: Most of this code is borrowed heavily from the original softlockup
* detector, so thanks to Ingo for the initial implementation.
* Some chunks also taken from the old x86-specific nmi watchdog code, thanks
* to those contributors as well.
*/
#define pr_fmt(fmt) "NMI watchdog: " fmt
#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/kvm_para.h>
#include <linux/perf_event.h>
int watchdog_enabled = 1;
int __read_mostly watchdog_thresh = 10;
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, softlockup_touch_sync);
static DEFINE_PER_CPU(bool, soft_watchdog_warn);
#ifdef CONFIG_HARDLOCKUP_DETECTOR
static DEFINE_PER_CPU(bool, hard_watchdog_warn);
static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
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
/* boot commands */
/*
* Should we panic when a soft-lockup or hard-lockup occurs:
*/
#ifdef CONFIG_HARDLOCKUP_DETECTOR
static int hardlockup_panic =
CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
static int __init hardlockup_panic_setup(char *str)
{
if (!strncmp(str, "panic", 5))
hardlockup_panic = 1;
else if (!strncmp(str, "nopanic", 7))
hardlockup_panic = 0;
else if (!strncmp(str, "0", 1))
watchdog_enabled = 0;
return 1;
}
__setup("nmi_watchdog=", hardlockup_panic_setup);
#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)
{
watchdog_enabled = 0;
return 1;
}
__setup("nowatchdog", nowatchdog_setup);
/* deprecated */
static int __init nosoftlockup_setup(char *str)
{
watchdog_enabled = 0;
return 1;
}
__setup("nosoftlockup", nosoftlockup_setup);
/* */
/*
* Hard-lockup warnings should be triggered after just a few seconds. Soft-
* lockups can have false positives under extreme conditions. So we generally
* want a higher threshold for soft lockups than for hard lockups. So we couple
* the thresholds with a factor: we make the soft threshold twice the amount of
* time the hard threshold is.
*/
static int get_softlockup_thresh(void)
{
return watchdog_thresh * 2;
}
/*
* 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 watchdog_thresh from seconds to ns
* the divide by 5 is to give hrtimer several chances (two
* or three with the current relation between the soft
* and hard thresholds) to increment before the
* hardlockup detector generates a warning
*/
return get_softlockup_thresh() * (NSEC_PER_SEC / 5);
}
/* Commands for resetting the watchdog */
static void __touch_watchdog(void)
{
int this_cpu = smp_processor_id();
__this_cpu_write(watchdog_touch_ts, get_timestamp(this_cpu));
}
void touch_softlockup_watchdog(void)
{
__this_cpu_write(watchdog_touch_ts, 0);
}
EXPORT_SYMBOL(touch_softlockup_watchdog);
void touch_all_softlockup_watchdogs(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;
}
#ifdef CONFIG_HARDLOCKUP_DETECTOR
void touch_nmi_watchdog(void)
{
if (watchdog_enabled) {
unsigned cpu;
for_each_present_cpu(cpu) {
if (per_cpu(watchdog_nmi_touch, cpu) != true)
per_cpu(watchdog_nmi_touch, cpu) = true;
}
}
touch_softlockup_watchdog();
}
EXPORT_SYMBOL(touch_nmi_watchdog);
#endif
void touch_softlockup_watchdog_sync(void)
{
__raw_get_cpu_var(softlockup_touch_sync) = true;
__raw_get_cpu_var(watchdog_touch_ts) = 0;
}
#ifdef CONFIG_HARDLOCKUP_DETECTOR
/* watchdog detector functions */
static int is_hardlockup(void)
{
unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
return 1;
__this_cpu_write(hrtimer_interrupts_saved, hrint);
return 0;
}
#endif
static int is_softlockup(unsigned long touch_ts)
{
unsigned long now = get_timestamp(smp_processor_id());
/* Warn about unreasonable delays: */
if (time_after(now, touch_ts + get_softlockup_thresh()))
return now - touch_ts;
return 0;
}
#ifdef CONFIG_HARDLOCKUP_DETECTOR
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 */
static void watchdog_overflow_callback(struct perf_event *event,
struct perf_sample_data *data,
struct pt_regs *regs)
{
/* Ensure the watchdog never gets throttled */
event->hw.interrupts = 0;
if (__this_cpu_read(watchdog_nmi_touch) == true) {
__this_cpu_write(watchdog_nmi_touch, false);
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()) {
int this_cpu = smp_processor_id();
/* only print hardlockups once */
if (__this_cpu_read(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);
__this_cpu_write(hard_watchdog_warn, true);
return;
}
__this_cpu_write(hard_watchdog_warn, false);
return;
}
static void watchdog_interrupt_count(void)
{
__this_cpu_inc(hrtimer_interrupts);
}
#else
static inline void watchdog_interrupt_count(void) { return; }
#endif /* CONFIG_HARDLOCKUP_DETECTOR */
/* watchdog kicker functions */
static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
{
unsigned long touch_ts = __this_cpu_read(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(__this_cpu_read(softlockup_watchdog));
/* .. and repeat */
hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
if (touch_ts == 0) {
if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
/*
* If the time stamp was touched atomically
* make sure the scheduler tick is up to date.
*/
__this_cpu_write(softlockup_touch_sync, false);
sched_clock_tick();
}
/* Clear the guest paused flag on watchdog reset */
kvm_check_and_clear_guest_paused();
__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);
if (unlikely(duration)) {
/*
* If a virtual machine is stopped by the host it can look to
* the watchdog like a soft lockup, check to see if the host
* stopped the vm before we issue the warning
*/
if (kvm_check_and_clear_guest_paused())
return HRTIMER_RESTART;
/* only warn once */
if (__this_cpu_read(soft_watchdog_warn) == true)
return HRTIMER_RESTART;
printk(KERN_EMERG "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
smp_processor_id(), 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");
__this_cpu_write(soft_watchdog_warn, true);
} else
__this_cpu_write(soft_watchdog_warn, false);
return HRTIMER_RESTART;
}
/*
* The watchdog thread - touches the timestamp.
*/
static int watchdog(void *unused)
{
struct sched_param param = { .sched_priority = 0 };
struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
/* initialize timestamp */
__touch_watchdog();
/* kick off the timer for the hardlockup detector */
/* done here because hrtimer_start can only pin to smp_processor_id() */
hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()),
HRTIMER_MODE_REL_PINNED);
set_current_state(TASK_INTERRUPTIBLE);
/*
* Run briefly (kicked by the hrtimer callback function) once every
* get_sample_period() seconds (4 seconds by default) to reset the
* softlockup timestamp. If this gets delayed for more than
* 2*watchdog_thresh seconds then the debug-printout triggers in
* watchdog_timer_fn().
*/
while (!kthread_should_stop()) {
__touch_watchdog();
schedule();
if (kthread_should_stop())
break;
set_current_state(TASK_INTERRUPTIBLE);
}
/*
* Drop the policy/priority elevation during thread exit to avoid a
* scheduling latency spike.
*/
__set_current_state(TASK_RUNNING);
sched_setscheduler(current, SCHED_NORMAL, &param);
return 0;
}
#ifdef CONFIG_HARDLOCKUP_DETECTOR
/*
* People like the simple clean cpu node info on boot.
* Reduce the watchdog noise by only printing messages
* that are different from what cpu0 displayed.
*/
static unsigned long cpu0_err;
static int watchdog_nmi_enable(int cpu)
{
struct perf_event_attr *wd_attr;
struct perf_event *event = per_cpu(watchdog_ev, cpu);
/* is it already setup and enabled? */
if (event && event->state > PERF_EVENT_STATE_OFF)
goto out;
/* it is setup but not enabled */
if (event != NULL)
goto out_enable;
wd_attr = &wd_hw_attr;
wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
/* Try to register using hardware perf events */
event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
/* save cpu0 error for future comparision */
if (cpu == 0 && IS_ERR(event))
cpu0_err = PTR_ERR(event);
if (!IS_ERR(event)) {
/* only print for cpu0 or different than cpu0 */
if (cpu == 0 || cpu0_err)
pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
goto out_save;
}
/* skip displaying the same error again */
if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
return PTR_ERR(event);
/* vary the KERN level based on the returned errno */
if (PTR_ERR(event) == -EOPNOTSUPP)
pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
else if (PTR_ERR(event) == -ENOENT)
pr_warning("disabled (cpu%i): hardware events not enabled\n",
cpu);
else
pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
cpu, PTR_ERR(event));
return PTR_ERR(event);
/* success path */
out_save:
per_cpu(watchdog_ev, cpu) = event;
out_enable:
perf_event_enable(per_cpu(watchdog_ev, cpu));
out:
return 0;
}
static void watchdog_nmi_disable(int cpu)
{
struct perf_event *event = per_cpu(watchdog_ev, cpu);
if (event) {
perf_event_disable(event);
per_cpu(watchdog_ev, cpu) = NULL;
/* should be in cleanup, but blocks oprofile */
perf_event_release_kernel(event);
}
return;
}
#else
static int watchdog_nmi_enable(int cpu) { return 0; }
static void watchdog_nmi_disable(int cpu) { return; }
#endif /* CONFIG_HARDLOCKUP_DETECTOR */
/* prepare/enable/disable routines */
static void watchdog_prepare_cpu(int cpu)
{
struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
WARN_ON(per_cpu(softlockup_watchdog, cpu));
hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
hrtimer->function = watchdog_timer_fn;
}
static int watchdog_enable(int cpu)
{
struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
int err = 0;
/* enable the perf event */
err = watchdog_nmi_enable(cpu);
/* Regardless of err above, fall through and start softlockup */
/* create the watchdog thread */
if (!p) {
struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
p = kthread_create_on_node(watchdog, NULL, cpu_to_node(cpu), "watchdog/%d", cpu);
if (IS_ERR(p)) {
pr_err("softlockup watchdog for %i failed\n", cpu);
if (!err) {
/* if hardlockup hasn't already set this */
err = PTR_ERR(p);
/* and disable the perf event */
watchdog_nmi_disable(cpu);
}
goto out;
}
sched_setscheduler(p, SCHED_FIFO, &param);
kthread_bind(p, cpu);
per_cpu(watchdog_touch_ts, cpu) = 0;
per_cpu(softlockup_watchdog, cpu) = p;
wake_up_process(p);
}
out:
return err;
}
static void watchdog_disable(int cpu)
{
struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
/*
* cancel the timer first to stop incrementing the stats
* and waking up the kthread
*/
hrtimer_cancel(hrtimer);
/* disable the perf event */
watchdog_nmi_disable(cpu);
/* stop the watchdog thread */
if (p) {
per_cpu(softlockup_watchdog, cpu) = NULL;
kthread_stop(p);
}
}
/* sysctl functions */
#ifdef CONFIG_SYSCTL
static void watchdog_enable_all_cpus(void)
{
int cpu;
watchdog_enabled = 0;
for_each_online_cpu(cpu)
if (!watchdog_enable(cpu))
/* if any cpu succeeds, watchdog is considered
enabled for the system */
watchdog_enabled = 1;
if (!watchdog_enabled)
pr_err("failed to be enabled on some cpus\n");
}
static void watchdog_disable_all_cpus(void)
{
int cpu;
for_each_online_cpu(cpu)
watchdog_disable(cpu);
/* if all watchdogs are disabled, then they are disabled for the system */
watchdog_enabled = 0;
}
/*
* proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
*/
int proc_dowatchdog(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
int ret;
ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
if (ret || !write)
goto out;
if (watchdog_enabled && watchdog_thresh)
watchdog_enable_all_cpus();
else
watchdog_disable_all_cpus();
out:
return ret;
}
#endif /* CONFIG_SYSCTL */
/*
* Create/destroy watchdog threads as CPUs come and go:
*/
static int
cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
{
int hotcpu = (unsigned long)hcpu;
switch (action) {
case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
watchdog_prepare_cpu(hotcpu);
break;
case CPU_ONLINE:
case CPU_ONLINE_FROZEN:
if (watchdog_enabled)
watchdog_enable(hotcpu);
break;
#ifdef CONFIG_HOTPLUG_CPU
case CPU_UP_CANCELED:
case CPU_UP_CANCELED_FROZEN:
watchdog_disable(hotcpu);
break;
case CPU_DEAD:
case CPU_DEAD_FROZEN:
watchdog_disable(hotcpu);
break;
#endif /* CONFIG_HOTPLUG_CPU */
}
/*
* hardlockup and softlockup are not important enough
* to block cpu bring up. Just always succeed and
* rely on printk output to flag problems.
*/
return NOTIFY_OK;
}
static struct notifier_block cpu_nfb = {
.notifier_call = cpu_callback
};
#ifdef CONFIG_SUSPEND
/*
* On exit from suspend we force an offline->online transition on the boot CPU
* so that the PMU state that was lost while in suspended state gets set up
* properly for the boot CPU. This information is required for restarting the
* NMI watchdog.
*/
void lockup_detector_bootcpu_resume(void)
{
void *cpu = (void *)(long)smp_processor_id();
cpu_callback(&cpu_nfb, CPU_DEAD_FROZEN, cpu);
cpu_callback(&cpu_nfb, CPU_UP_PREPARE_FROZEN, cpu);
cpu_callback(&cpu_nfb, CPU_ONLINE_FROZEN, cpu);
}
#endif
void __init lockup_detector_init(void)
{
void *cpu = (void *)(long)smp_processor_id();
int err;
err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
WARN_ON(notifier_to_errno(err));
cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
register_cpu_notifier(&cpu_nfb);
return;
}