| // SPDX-License-Identifier: GPL-2.0 |
| /* |
| * Detect hard lockups on a system using perf |
| * |
| * 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/nmi.h> |
| #include <linux/atomic.h> |
| #include <linux/module.h> |
| #include <linux/sched/debug.h> |
| |
| #include <asm/irq_regs.h> |
| #include <linux/perf_event.h> |
| |
| static DEFINE_PER_CPU(struct perf_event *, watchdog_ev); |
| static DEFINE_PER_CPU(struct perf_event *, dead_event); |
| static struct cpumask dead_events_mask; |
| |
| static atomic_t watchdog_cpus = ATOMIC_INIT(0); |
| |
| #ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP |
| static DEFINE_PER_CPU(ktime_t, last_timestamp); |
| static DEFINE_PER_CPU(unsigned int, nmi_rearmed); |
| static ktime_t watchdog_hrtimer_sample_threshold __read_mostly; |
| |
| void watchdog_update_hrtimer_threshold(u64 period) |
| { |
| /* |
| * The hrtimer runs with a period of (watchdog_threshold * 2) / 5 |
| * |
| * So it runs effectively with 2.5 times the rate of the NMI |
| * watchdog. That means the hrtimer should fire 2-3 times before |
| * the NMI watchdog expires. The NMI watchdog on x86 is based on |
| * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles |
| * might run way faster than expected and the NMI fires in a |
| * smaller period than the one deduced from the nominal CPU |
| * frequency. Depending on the Turbo-Mode factor this might be fast |
| * enough to get the NMI period smaller than the hrtimer watchdog |
| * period and trigger false positives. |
| * |
| * The sample threshold is used to check in the NMI handler whether |
| * the minimum time between two NMI samples has elapsed. That |
| * prevents false positives. |
| * |
| * Set this to 4/5 of the actual watchdog threshold period so the |
| * hrtimer is guaranteed to fire at least once within the real |
| * watchdog threshold. |
| */ |
| watchdog_hrtimer_sample_threshold = period * 2; |
| } |
| |
| static bool watchdog_check_timestamp(void) |
| { |
| ktime_t delta, now = ktime_get_mono_fast_ns(); |
| |
| delta = now - __this_cpu_read(last_timestamp); |
| if (delta < watchdog_hrtimer_sample_threshold) { |
| /* |
| * If ktime is jiffies based, a stalled timer would prevent |
| * jiffies from being incremented and the filter would look |
| * at a stale timestamp and never trigger. |
| */ |
| if (__this_cpu_inc_return(nmi_rearmed) < 10) |
| return false; |
| } |
| __this_cpu_write(nmi_rearmed, 0); |
| __this_cpu_write(last_timestamp, now); |
| return true; |
| } |
| #else |
| static inline bool watchdog_check_timestamp(void) |
| { |
| return true; |
| } |
| #endif |
| |
| 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 (!watchdog_check_timestamp()) |
| return; |
| |
| watchdog_hardlockup_check(smp_processor_id(), regs); |
| } |
| |
| static int hardlockup_detector_event_create(void) |
| { |
| unsigned int cpu; |
| struct perf_event_attr *wd_attr; |
| struct perf_event *evt; |
| |
| /* |
| * Preemption is not disabled because memory will be allocated. |
| * Ensure CPU-locality by calling this in per-CPU kthread. |
| */ |
| WARN_ON(!is_percpu_thread()); |
| cpu = raw_smp_processor_id(); |
| wd_attr = &wd_hw_attr; |
| wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh); |
| |
| /* Try to register using hardware perf events */ |
| evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL, |
| watchdog_overflow_callback, NULL); |
| if (IS_ERR(evt)) { |
| pr_debug("Perf event create on CPU %d failed with %ld\n", cpu, |
| PTR_ERR(evt)); |
| return PTR_ERR(evt); |
| } |
| this_cpu_write(watchdog_ev, evt); |
| return 0; |
| } |
| |
| /** |
| * watchdog_hardlockup_enable - Enable the local event |
| * |
| * @cpu: The CPU to enable hard lockup on. |
| */ |
| void watchdog_hardlockup_enable(unsigned int cpu) |
| { |
| WARN_ON_ONCE(cpu != smp_processor_id()); |
| |
| if (hardlockup_detector_event_create()) |
| return; |
| |
| /* use original value for check */ |
| if (!atomic_fetch_inc(&watchdog_cpus)) |
| pr_info("Enabled. Permanently consumes one hw-PMU counter.\n"); |
| |
| perf_event_enable(this_cpu_read(watchdog_ev)); |
| } |
| |
| /** |
| * watchdog_hardlockup_disable - Disable the local event |
| * |
| * @cpu: The CPU to enable hard lockup on. |
| */ |
| void watchdog_hardlockup_disable(unsigned int cpu) |
| { |
| struct perf_event *event = this_cpu_read(watchdog_ev); |
| |
| WARN_ON_ONCE(cpu != smp_processor_id()); |
| |
| if (event) { |
| perf_event_disable(event); |
| this_cpu_write(watchdog_ev, NULL); |
| this_cpu_write(dead_event, event); |
| cpumask_set_cpu(smp_processor_id(), &dead_events_mask); |
| atomic_dec(&watchdog_cpus); |
| } |
| } |
| |
| /** |
| * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them |
| * |
| * Called from lockup_detector_cleanup(). Serialized by the caller. |
| */ |
| void hardlockup_detector_perf_cleanup(void) |
| { |
| int cpu; |
| |
| for_each_cpu(cpu, &dead_events_mask) { |
| struct perf_event *event = per_cpu(dead_event, cpu); |
| |
| /* |
| * Required because for_each_cpu() reports unconditionally |
| * CPU0 as set on UP kernels. Sigh. |
| */ |
| if (event) |
| perf_event_release_kernel(event); |
| per_cpu(dead_event, cpu) = NULL; |
| } |
| cpumask_clear(&dead_events_mask); |
| } |
| |
| /** |
| * hardlockup_detector_perf_stop - Globally stop watchdog events |
| * |
| * Special interface for x86 to handle the perf HT bug. |
| */ |
| void __init hardlockup_detector_perf_stop(void) |
| { |
| int cpu; |
| |
| lockdep_assert_cpus_held(); |
| |
| for_each_online_cpu(cpu) { |
| struct perf_event *event = per_cpu(watchdog_ev, cpu); |
| |
| if (event) |
| perf_event_disable(event); |
| } |
| } |
| |
| /** |
| * hardlockup_detector_perf_restart - Globally restart watchdog events |
| * |
| * Special interface for x86 to handle the perf HT bug. |
| */ |
| void __init hardlockup_detector_perf_restart(void) |
| { |
| int cpu; |
| |
| lockdep_assert_cpus_held(); |
| |
| if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED)) |
| return; |
| |
| for_each_online_cpu(cpu) { |
| struct perf_event *event = per_cpu(watchdog_ev, cpu); |
| |
| if (event) |
| perf_event_enable(event); |
| } |
| } |
| |
| bool __weak __init arch_perf_nmi_is_available(void) |
| { |
| return true; |
| } |
| |
| /** |
| * watchdog_hardlockup_probe - Probe whether NMI event is available at all |
| */ |
| int __init watchdog_hardlockup_probe(void) |
| { |
| int ret; |
| |
| if (!arch_perf_nmi_is_available()) |
| return -ENODEV; |
| |
| ret = hardlockup_detector_event_create(); |
| |
| if (ret) { |
| pr_info("Perf NMI watchdog permanently disabled\n"); |
| } else { |
| perf_event_release_kernel(this_cpu_read(watchdog_ev)); |
| this_cpu_write(watchdog_ev, NULL); |
| } |
| return ret; |
| } |