![Thomas Gleixner](/assets/img/avatar_default.png)
Guenter reported a crash in the watchdog/perf code, which is caused by cleanup() and enable() running concurrently. The reason for this is: The watchdog functions are serialized via the watchdog_mutex and cpu hotplug locking, but the enable of the perf based watchdog happens in context of the unpark callback of the smpboot thread. But that unpark function is not synchronous inside the locking. The unparking of the thread just wakes it up and leaves so there is no guarantee when the thread is executing. If it starts running _before_ the cleanup happened then it will create a event and overwrite the dead event pointer. The new event is then cleaned up because the event is marked dead. lock(watchdog_mutex); lockup_detector_reconfigure(); cpus_read_lock(); stop(); park() update(); start(); unpark() cpus_read_unlock(); thread runs() overwrite dead event ptr cleanup(); free new event, which is active inside perf.... unlock(watchdog_mutex); The park side is safe as that actually waits for the thread to reach parked state. Commita33d44843d
removed the protection against this kind of scenario under the stupid assumption that the hotplug serialization and the watchdog_mutex cover everything. Bring it back. Reverts:a33d44843d
("watchdog/hardlockup/perf: Simplify deferred event destroy") Reported-and-tested-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Thomas Feels-stupid Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Don Zickus <dzickus@redhat.com> Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1710312145190.1942@nanos
293 lines
7.5 KiB
C
293 lines
7.5 KiB
C
/*
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* Detect hard lockups on a system
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*
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* started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
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*
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* Note: Most of this code is borrowed heavily from the original softlockup
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* detector, so thanks to Ingo for the initial implementation.
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* Some chunks also taken from the old x86-specific nmi watchdog code, thanks
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* to those contributors as well.
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*/
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#define pr_fmt(fmt) "NMI watchdog: " fmt
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#include <linux/nmi.h>
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#include <linux/module.h>
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#include <linux/sched/debug.h>
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#include <asm/irq_regs.h>
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#include <linux/perf_event.h>
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static DEFINE_PER_CPU(bool, hard_watchdog_warn);
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static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
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static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
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static DEFINE_PER_CPU(struct perf_event *, dead_event);
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static struct cpumask dead_events_mask;
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static unsigned long hardlockup_allcpu_dumped;
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static unsigned int watchdog_cpus;
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void arch_touch_nmi_watchdog(void)
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{
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/*
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* Using __raw here because some code paths have
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* preemption enabled. If preemption is enabled
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* then interrupts should be enabled too, in which
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* case we shouldn't have to worry about the watchdog
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* going off.
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*/
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raw_cpu_write(watchdog_nmi_touch, true);
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}
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EXPORT_SYMBOL(arch_touch_nmi_watchdog);
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#ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
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static DEFINE_PER_CPU(ktime_t, last_timestamp);
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static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
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static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
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void watchdog_update_hrtimer_threshold(u64 period)
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{
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/*
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* The hrtimer runs with a period of (watchdog_threshold * 2) / 5
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*
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* So it runs effectively with 2.5 times the rate of the NMI
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* watchdog. That means the hrtimer should fire 2-3 times before
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* the NMI watchdog expires. The NMI watchdog on x86 is based on
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* unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
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* might run way faster than expected and the NMI fires in a
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* smaller period than the one deduced from the nominal CPU
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* frequency. Depending on the Turbo-Mode factor this might be fast
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* enough to get the NMI period smaller than the hrtimer watchdog
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* period and trigger false positives.
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*
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* The sample threshold is used to check in the NMI handler whether
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* the minimum time between two NMI samples has elapsed. That
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* prevents false positives.
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*
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* Set this to 4/5 of the actual watchdog threshold period so the
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* hrtimer is guaranteed to fire at least once within the real
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* watchdog threshold.
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*/
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watchdog_hrtimer_sample_threshold = period * 2;
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}
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static bool watchdog_check_timestamp(void)
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{
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ktime_t delta, now = ktime_get_mono_fast_ns();
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delta = now - __this_cpu_read(last_timestamp);
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if (delta < watchdog_hrtimer_sample_threshold) {
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/*
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* If ktime is jiffies based, a stalled timer would prevent
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* jiffies from being incremented and the filter would look
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* at a stale timestamp and never trigger.
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*/
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if (__this_cpu_inc_return(nmi_rearmed) < 10)
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return false;
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}
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__this_cpu_write(nmi_rearmed, 0);
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__this_cpu_write(last_timestamp, now);
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return true;
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}
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#else
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static inline bool watchdog_check_timestamp(void)
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{
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return true;
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}
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#endif
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static struct perf_event_attr wd_hw_attr = {
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.type = PERF_TYPE_HARDWARE,
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.config = PERF_COUNT_HW_CPU_CYCLES,
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.size = sizeof(struct perf_event_attr),
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.pinned = 1,
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.disabled = 1,
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};
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/* Callback function for perf event subsystem */
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static void watchdog_overflow_callback(struct perf_event *event,
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struct perf_sample_data *data,
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struct pt_regs *regs)
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{
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/* Ensure the watchdog never gets throttled */
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event->hw.interrupts = 0;
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if (__this_cpu_read(watchdog_nmi_touch) == true) {
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__this_cpu_write(watchdog_nmi_touch, false);
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return;
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}
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if (!watchdog_check_timestamp())
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return;
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/* check for a hardlockup
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* This is done by making sure our timer interrupt
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* is incrementing. The timer interrupt should have
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* fired multiple times before we overflow'd. If it hasn't
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* then this is a good indication the cpu is stuck
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*/
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if (is_hardlockup()) {
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int this_cpu = smp_processor_id();
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/* only print hardlockups once */
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if (__this_cpu_read(hard_watchdog_warn) == true)
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return;
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pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
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print_modules();
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print_irqtrace_events(current);
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if (regs)
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show_regs(regs);
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else
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dump_stack();
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/*
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* Perform all-CPU dump only once to avoid multiple hardlockups
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* generating interleaving traces
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*/
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if (sysctl_hardlockup_all_cpu_backtrace &&
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!test_and_set_bit(0, &hardlockup_allcpu_dumped))
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trigger_allbutself_cpu_backtrace();
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if (hardlockup_panic)
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nmi_panic(regs, "Hard LOCKUP");
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__this_cpu_write(hard_watchdog_warn, true);
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return;
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}
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__this_cpu_write(hard_watchdog_warn, false);
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return;
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}
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static int hardlockup_detector_event_create(void)
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{
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unsigned int cpu = smp_processor_id();
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struct perf_event_attr *wd_attr;
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struct perf_event *evt;
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wd_attr = &wd_hw_attr;
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wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
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/* Try to register using hardware perf events */
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evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
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watchdog_overflow_callback, NULL);
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if (IS_ERR(evt)) {
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pr_info("Perf event create on CPU %d failed with %ld\n", cpu,
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PTR_ERR(evt));
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return PTR_ERR(evt);
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}
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this_cpu_write(watchdog_ev, evt);
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return 0;
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}
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/**
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* hardlockup_detector_perf_enable - Enable the local event
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*/
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void hardlockup_detector_perf_enable(void)
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{
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if (hardlockup_detector_event_create())
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return;
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if (!watchdog_cpus++)
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pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
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perf_event_enable(this_cpu_read(watchdog_ev));
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}
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/**
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* hardlockup_detector_perf_disable - Disable the local event
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*/
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void hardlockup_detector_perf_disable(void)
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{
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struct perf_event *event = this_cpu_read(watchdog_ev);
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if (event) {
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perf_event_disable(event);
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this_cpu_write(watchdog_ev, NULL);
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this_cpu_write(dead_event, event);
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cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
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watchdog_cpus--;
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}
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}
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/**
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* hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
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*
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* Called from lockup_detector_cleanup(). Serialized by the caller.
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*/
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void hardlockup_detector_perf_cleanup(void)
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{
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int cpu;
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for_each_cpu(cpu, &dead_events_mask) {
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struct perf_event *event = per_cpu(dead_event, cpu);
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/*
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* Required because for_each_cpu() reports unconditionally
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* CPU0 as set on UP kernels. Sigh.
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*/
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if (event)
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perf_event_release_kernel(event);
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per_cpu(dead_event, cpu) = NULL;
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}
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cpumask_clear(&dead_events_mask);
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}
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/**
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* hardlockup_detector_perf_stop - Globally stop watchdog events
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*
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* Special interface for x86 to handle the perf HT bug.
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*/
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void __init hardlockup_detector_perf_stop(void)
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{
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int cpu;
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lockdep_assert_cpus_held();
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for_each_online_cpu(cpu) {
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struct perf_event *event = per_cpu(watchdog_ev, cpu);
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if (event)
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perf_event_disable(event);
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}
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}
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/**
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* hardlockup_detector_perf_restart - Globally restart watchdog events
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*
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* Special interface for x86 to handle the perf HT bug.
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*/
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void __init hardlockup_detector_perf_restart(void)
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{
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int cpu;
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lockdep_assert_cpus_held();
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if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
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return;
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for_each_online_cpu(cpu) {
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struct perf_event *event = per_cpu(watchdog_ev, cpu);
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if (event)
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perf_event_enable(event);
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}
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}
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/**
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* hardlockup_detector_perf_init - Probe whether NMI event is available at all
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*/
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int __init hardlockup_detector_perf_init(void)
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{
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int ret = hardlockup_detector_event_create();
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if (ret) {
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pr_info("Perf NMI watchdog permanently disabled\n");
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} else {
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perf_event_release_kernel(this_cpu_read(watchdog_ev));
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this_cpu_write(watchdog_ev, NULL);
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}
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return ret;
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}
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