| // SPDX-License-Identifier: GPL-2.0 |
| /* |
| * Detect hard 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/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(bool, hard_watchdog_warn); |
| static DEFINE_PER_CPU(bool, watchdog_nmi_touch); |
| 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 unsigned long hardlockup_allcpu_dumped; |
| static atomic_t watchdog_cpus = ATOMIC_INIT(0); |
| |
| notrace void arch_touch_nmi_watchdog(void) |
| { |
| /* |
| * Using __raw here because some code paths have |
| * preemption enabled. If preemption is enabled |
| * then interrupts should be enabled too, in which |
| * case we shouldn't have to worry about the watchdog |
| * going off. |
| */ |
| raw_cpu_write(watchdog_nmi_touch, true); |
| } |
| EXPORT_SYMBOL(arch_touch_nmi_watchdog); |
| |
| #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 (__this_cpu_read(watchdog_nmi_touch) == true) { |
| __this_cpu_write(watchdog_nmi_touch, false); |
| return; |
| } |
| |
| if (!watchdog_check_timestamp()) |
| 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; |
| |
| printk_prefer_direct_enter(); |
| |
| pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n", |
| this_cpu); |
| print_modules(); |
| print_irqtrace_events(current); |
| if (regs) |
| show_regs(regs); |
| else |
| dump_stack(); |
| |
| /* |
| * Perform all-CPU dump only once to avoid multiple hardlockups |
| * generating interleaving traces |
| */ |
| if (sysctl_hardlockup_all_cpu_backtrace && |
| !test_and_set_bit(0, &hardlockup_allcpu_dumped)) |
| trigger_allbutself_cpu_backtrace(); |
| |
| if (hardlockup_panic) |
| nmi_panic(regs, "Hard LOCKUP"); |
| |
| printk_prefer_direct_exit(); |
| |
| __this_cpu_write(hard_watchdog_warn, true); |
| return; |
| } |
| |
| __this_cpu_write(hard_watchdog_warn, false); |
| return; |
| } |
| |
| static int hardlockup_detector_event_create(void) |
| { |
| unsigned int cpu = smp_processor_id(); |
| struct perf_event_attr *wd_attr; |
| struct perf_event *evt; |
| |
| 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; |
| } |