// 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 #include #include #include #include #include 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; } /** * hardlockup_detector_perf_enable - Enable the local event */ void hardlockup_detector_perf_enable(void) { 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)); } /** * hardlockup_detector_perf_disable - Disable the local event */ void hardlockup_detector_perf_disable(void) { struct perf_event *event = this_cpu_read(watchdog_ev); 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 & NMI_WATCHDOG_ENABLED)) return; for_each_online_cpu(cpu) { struct perf_event *event = per_cpu(watchdog_ev, cpu); if (event) perf_event_enable(event); } } /** * hardlockup_detector_perf_init - Probe whether NMI event is available at all */ int __init hardlockup_detector_perf_init(void) { int 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; }