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572 lines
16 KiB
572 lines
16 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* |
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* Watchdog support on powerpc systems. |
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* |
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* Copyright 2017, IBM Corporation. |
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* |
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* This uses code from arch/sparc/kernel/nmi.c and kernel/watchdog.c |
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*/ |
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|
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#define pr_fmt(fmt) "watchdog: " fmt |
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#include <linux/kernel.h> |
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#include <linux/param.h> |
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#include <linux/init.h> |
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#include <linux/percpu.h> |
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#include <linux/cpu.h> |
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#include <linux/nmi.h> |
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#include <linux/module.h> |
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#include <linux/export.h> |
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#include <linux/kprobes.h> |
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#include <linux/hardirq.h> |
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#include <linux/reboot.h> |
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#include <linux/slab.h> |
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#include <linux/kdebug.h> |
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#include <linux/sched/debug.h> |
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#include <linux/delay.h> |
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#include <linux/processor.h> |
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#include <linux/smp.h> |
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#include <asm/interrupt.h> |
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#include <asm/paca.h> |
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#include <asm/nmi.h> |
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/* |
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* The powerpc watchdog ensures that each CPU is able to service timers. |
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* The watchdog sets up a simple timer on each CPU to run once per timer |
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* period, and updates a per-cpu timestamp and a "pending" cpumask. This is |
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* the heartbeat. |
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* |
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* Then there are two systems to check that the heartbeat is still running. |
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* The local soft-NMI, and the SMP checker. |
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* |
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* The soft-NMI checker can detect lockups on the local CPU. When interrupts |
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* are disabled with local_irq_disable(), platforms that use soft-masking |
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* can leave hardware interrupts enabled and handle them with a masked |
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* interrupt handler. The masked handler can send the timer interrupt to the |
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* watchdog's soft_nmi_interrupt(), which appears to Linux as an NMI |
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* interrupt, and can be used to detect CPUs stuck with IRQs disabled. |
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* |
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* The soft-NMI checker will compare the heartbeat timestamp for this CPU |
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* with the current time, and take action if the difference exceeds the |
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* watchdog threshold. |
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* |
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* The limitation of the soft-NMI watchdog is that it does not work when |
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* interrupts are hard disabled or otherwise not being serviced. This is |
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* solved by also having a SMP watchdog where all CPUs check all other |
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* CPUs heartbeat. |
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* |
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* The SMP checker can detect lockups on other CPUs. A gobal "pending" |
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* cpumask is kept, containing all CPUs which enable the watchdog. Each |
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* CPU clears their pending bit in their heartbeat timer. When the bitmask |
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* becomes empty, the last CPU to clear its pending bit updates a global |
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* timestamp and refills the pending bitmask. |
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* |
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* In the heartbeat timer, if any CPU notices that the global timestamp has |
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* not been updated for a period exceeding the watchdog threshold, then it |
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* means the CPU(s) with their bit still set in the pending mask have had |
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* their heartbeat stop, and action is taken. |
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* |
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* Some platforms implement true NMI IPIs, which can be used by the SMP |
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* watchdog to detect an unresponsive CPU and pull it out of its stuck |
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* state with the NMI IPI, to get crash/debug data from it. This way the |
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* SMP watchdog can detect hardware interrupts off lockups. |
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*/ |
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static cpumask_t wd_cpus_enabled __read_mostly; |
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static u64 wd_panic_timeout_tb __read_mostly; /* timebase ticks until panic */ |
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static u64 wd_smp_panic_timeout_tb __read_mostly; /* panic other CPUs */ |
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static u64 wd_timer_period_ms __read_mostly; /* interval between heartbeat */ |
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static DEFINE_PER_CPU(struct hrtimer, wd_hrtimer); |
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static DEFINE_PER_CPU(u64, wd_timer_tb); |
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/* SMP checker bits */ |
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static unsigned long __wd_smp_lock; |
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static unsigned long __wd_reporting; |
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static unsigned long __wd_nmi_output; |
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static cpumask_t wd_smp_cpus_pending; |
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static cpumask_t wd_smp_cpus_stuck; |
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static u64 wd_smp_last_reset_tb; |
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/* |
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* Try to take the exclusive watchdog action / NMI IPI / printing lock. |
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* wd_smp_lock must be held. If this fails, we should return and wait |
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* for the watchdog to kick in again (or another CPU to trigger it). |
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* |
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* Importantly, if hardlockup_panic is set, wd_try_report failure should |
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* not delay the panic, because whichever other CPU is reporting will |
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* call panic. |
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*/ |
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static bool wd_try_report(void) |
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{ |
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if (__wd_reporting) |
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return false; |
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__wd_reporting = 1; |
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return true; |
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} |
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/* End printing after successful wd_try_report. wd_smp_lock not required. */ |
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static void wd_end_reporting(void) |
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{ |
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smp_mb(); /* End printing "critical section" */ |
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WARN_ON_ONCE(__wd_reporting == 0); |
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WRITE_ONCE(__wd_reporting, 0); |
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} |
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static inline void wd_smp_lock(unsigned long *flags) |
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{ |
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/* |
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* Avoid locking layers if possible. |
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* This may be called from low level interrupt handlers at some |
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* point in future. |
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*/ |
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raw_local_irq_save(*flags); |
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hard_irq_disable(); /* Make it soft-NMI safe */ |
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while (unlikely(test_and_set_bit_lock(0, &__wd_smp_lock))) { |
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raw_local_irq_restore(*flags); |
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spin_until_cond(!test_bit(0, &__wd_smp_lock)); |
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raw_local_irq_save(*flags); |
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hard_irq_disable(); |
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} |
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} |
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static inline void wd_smp_unlock(unsigned long *flags) |
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{ |
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clear_bit_unlock(0, &__wd_smp_lock); |
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raw_local_irq_restore(*flags); |
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} |
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static void wd_lockup_ipi(struct pt_regs *regs) |
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{ |
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int cpu = raw_smp_processor_id(); |
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u64 tb = get_tb(); |
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pr_emerg("CPU %d Hard LOCKUP\n", cpu); |
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pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n", |
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cpu, tb, per_cpu(wd_timer_tb, cpu), |
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tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000); |
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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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* __wd_nmi_output must be set after we printk from NMI context. |
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* |
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* printk from NMI context defers printing to the console to irq_work. |
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* If that NMI was taken in some code that is hard-locked, then irqs |
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* are disabled so irq_work will never fire. That can result in the |
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* hard lockup messages being delayed (indefinitely, until something |
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* else kicks the console drivers). |
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* |
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* Setting __wd_nmi_output will cause another CPU to notice and kick |
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* the console drivers for us. |
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* |
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* xchg is not needed here (it could be a smp_mb and store), but xchg |
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* gives the memory ordering and atomicity required. |
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*/ |
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xchg(&__wd_nmi_output, 1); |
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/* Do not panic from here because that can recurse into NMI IPI layer */ |
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} |
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static bool set_cpu_stuck(int cpu) |
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{ |
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cpumask_set_cpu(cpu, &wd_smp_cpus_stuck); |
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cpumask_clear_cpu(cpu, &wd_smp_cpus_pending); |
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/* |
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* See wd_smp_clear_cpu_pending() |
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*/ |
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smp_mb(); |
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if (cpumask_empty(&wd_smp_cpus_pending)) { |
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wd_smp_last_reset_tb = get_tb(); |
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cpumask_andnot(&wd_smp_cpus_pending, |
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&wd_cpus_enabled, |
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&wd_smp_cpus_stuck); |
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return true; |
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} |
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return false; |
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} |
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static void watchdog_smp_panic(int cpu) |
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{ |
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static cpumask_t wd_smp_cpus_ipi; // protected by reporting |
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unsigned long flags; |
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u64 tb, last_reset; |
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int c; |
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wd_smp_lock(&flags); |
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/* Double check some things under lock */ |
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tb = get_tb(); |
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last_reset = wd_smp_last_reset_tb; |
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if ((s64)(tb - last_reset) < (s64)wd_smp_panic_timeout_tb) |
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goto out; |
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if (cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) |
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goto out; |
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if (!wd_try_report()) |
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goto out; |
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for_each_online_cpu(c) { |
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if (!cpumask_test_cpu(c, &wd_smp_cpus_pending)) |
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continue; |
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if (c == cpu) |
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continue; // should not happen |
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__cpumask_set_cpu(c, &wd_smp_cpus_ipi); |
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if (set_cpu_stuck(c)) |
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break; |
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} |
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if (cpumask_empty(&wd_smp_cpus_ipi)) { |
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wd_end_reporting(); |
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goto out; |
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} |
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wd_smp_unlock(&flags); |
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pr_emerg("CPU %d detected hard LOCKUP on other CPUs %*pbl\n", |
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cpu, cpumask_pr_args(&wd_smp_cpus_ipi)); |
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pr_emerg("CPU %d TB:%lld, last SMP heartbeat TB:%lld (%lldms ago)\n", |
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cpu, tb, last_reset, tb_to_ns(tb - last_reset) / 1000000); |
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if (!sysctl_hardlockup_all_cpu_backtrace) { |
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/* |
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* Try to trigger the stuck CPUs, unless we are going to |
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* get a backtrace on all of them anyway. |
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*/ |
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for_each_cpu(c, &wd_smp_cpus_ipi) { |
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smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000); |
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__cpumask_clear_cpu(c, &wd_smp_cpus_ipi); |
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} |
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} else { |
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trigger_allbutself_cpu_backtrace(); |
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cpumask_clear(&wd_smp_cpus_ipi); |
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} |
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if (hardlockup_panic) |
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nmi_panic(NULL, "Hard LOCKUP"); |
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wd_end_reporting(); |
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return; |
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out: |
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wd_smp_unlock(&flags); |
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} |
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static void wd_smp_clear_cpu_pending(int cpu) |
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{ |
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if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) { |
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if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) { |
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struct pt_regs *regs = get_irq_regs(); |
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unsigned long flags; |
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pr_emerg("CPU %d became unstuck TB:%lld\n", |
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cpu, get_tb()); |
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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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wd_smp_lock(&flags); |
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cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck); |
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wd_smp_unlock(&flags); |
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} else { |
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/* |
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* The last CPU to clear pending should have reset the |
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* watchdog so we generally should not find it empty |
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* here if our CPU was clear. However it could happen |
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* due to a rare race with another CPU taking the |
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* last CPU out of the mask concurrently. |
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* |
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* We can't add a warning for it. But just in case |
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* there is a problem with the watchdog that is causing |
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* the mask to not be reset, try to kick it along here. |
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*/ |
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if (unlikely(cpumask_empty(&wd_smp_cpus_pending))) |
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goto none_pending; |
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} |
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return; |
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} |
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/* |
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* All other updates to wd_smp_cpus_pending are performed under |
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* wd_smp_lock. All of them are atomic except the case where the |
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* mask becomes empty and is reset. This will not happen here because |
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* cpu was tested to be in the bitmap (above), and a CPU only clears |
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* its own bit. _Except_ in the case where another CPU has detected a |
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* hard lockup on our CPU and takes us out of the pending mask. So in |
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* normal operation there will be no race here, no problem. |
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* |
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* In the lockup case, this atomic clear-bit vs a store that refills |
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* other bits in the accessed word wll not be a problem. The bit clear |
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* is atomic so it will not cause the store to get lost, and the store |
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* will never set this bit so it will not overwrite the bit clear. The |
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* only way for a stuck CPU to return to the pending bitmap is to |
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* become unstuck itself. |
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*/ |
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cpumask_clear_cpu(cpu, &wd_smp_cpus_pending); |
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/* |
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* Order the store to clear pending with the load(s) to check all |
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* words in the pending mask to check they are all empty. This orders |
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* with the same barrier on another CPU. This prevents two CPUs |
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* clearing the last 2 pending bits, but neither seeing the other's |
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* store when checking if the mask is empty, and missing an empty |
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* mask, which ends with a false positive. |
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*/ |
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smp_mb(); |
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if (cpumask_empty(&wd_smp_cpus_pending)) { |
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unsigned long flags; |
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none_pending: |
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/* |
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* Double check under lock because more than one CPU could see |
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* a clear mask with the lockless check after clearing their |
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* pending bits. |
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*/ |
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wd_smp_lock(&flags); |
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if (cpumask_empty(&wd_smp_cpus_pending)) { |
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wd_smp_last_reset_tb = get_tb(); |
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cpumask_andnot(&wd_smp_cpus_pending, |
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&wd_cpus_enabled, |
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&wd_smp_cpus_stuck); |
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} |
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wd_smp_unlock(&flags); |
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} |
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} |
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static void watchdog_timer_interrupt(int cpu) |
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{ |
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u64 tb = get_tb(); |
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per_cpu(wd_timer_tb, cpu) = tb; |
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wd_smp_clear_cpu_pending(cpu); |
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if ((s64)(tb - wd_smp_last_reset_tb) >= (s64)wd_smp_panic_timeout_tb) |
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watchdog_smp_panic(cpu); |
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if (__wd_nmi_output && xchg(&__wd_nmi_output, 0)) { |
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/* |
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* Something has called printk from NMI context. It might be |
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* stuck, so this this triggers a flush that will get that |
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* printk output to the console. |
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* |
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* See wd_lockup_ipi. |
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*/ |
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printk_trigger_flush(); |
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} |
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} |
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DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt) |
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{ |
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unsigned long flags; |
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int cpu = raw_smp_processor_id(); |
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u64 tb; |
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/* should only arrive from kernel, with irqs disabled */ |
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WARN_ON_ONCE(!arch_irq_disabled_regs(regs)); |
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if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) |
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return 0; |
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__this_cpu_inc(irq_stat.soft_nmi_irqs); |
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tb = get_tb(); |
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if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) { |
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/* |
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* Taking wd_smp_lock here means it is a soft-NMI lock, which |
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* means we can't take any regular or irqsafe spin locks while |
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* holding this lock. This is why timers can't printk while |
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* holding the lock. |
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*/ |
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wd_smp_lock(&flags); |
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if (cpumask_test_cpu(cpu, &wd_smp_cpus_stuck)) { |
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wd_smp_unlock(&flags); |
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return 0; |
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} |
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if (!wd_try_report()) { |
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wd_smp_unlock(&flags); |
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/* Couldn't report, try again in 100ms */ |
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mtspr(SPRN_DEC, 100 * tb_ticks_per_usec * 1000); |
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return 0; |
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} |
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set_cpu_stuck(cpu); |
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wd_smp_unlock(&flags); |
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pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n", |
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cpu, (void *)regs->nip); |
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pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n", |
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cpu, tb, per_cpu(wd_timer_tb, cpu), |
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tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000); |
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print_modules(); |
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print_irqtrace_events(current); |
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show_regs(regs); |
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xchg(&__wd_nmi_output, 1); // see wd_lockup_ipi |
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if (sysctl_hardlockup_all_cpu_backtrace) |
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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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wd_end_reporting(); |
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} |
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/* |
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* We are okay to change DEC in soft_nmi_interrupt because the masked |
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* handler has marked a DEC as pending, so the timer interrupt will be |
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* replayed as soon as local irqs are enabled again. |
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*/ |
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if (wd_panic_timeout_tb < 0x7fffffff) |
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mtspr(SPRN_DEC, wd_panic_timeout_tb); |
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return 0; |
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} |
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static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) |
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{ |
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int cpu = smp_processor_id(); |
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if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) |
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return HRTIMER_NORESTART; |
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if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) |
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return HRTIMER_NORESTART; |
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watchdog_timer_interrupt(cpu); |
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hrtimer_forward_now(hrtimer, ms_to_ktime(wd_timer_period_ms)); |
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return HRTIMER_RESTART; |
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} |
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void arch_touch_nmi_watchdog(void) |
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{ |
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unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000; |
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int cpu = smp_processor_id(); |
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u64 tb; |
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if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) |
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return; |
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tb = get_tb(); |
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if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) { |
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per_cpu(wd_timer_tb, cpu) = tb; |
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wd_smp_clear_cpu_pending(cpu); |
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} |
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} |
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EXPORT_SYMBOL(arch_touch_nmi_watchdog); |
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static void start_watchdog(void *arg) |
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{ |
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struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer); |
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int cpu = smp_processor_id(); |
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unsigned long flags; |
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if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) { |
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WARN_ON(1); |
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return; |
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} |
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if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) |
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return; |
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if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) |
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return; |
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wd_smp_lock(&flags); |
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cpumask_set_cpu(cpu, &wd_cpus_enabled); |
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if (cpumask_weight(&wd_cpus_enabled) == 1) { |
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cpumask_set_cpu(cpu, &wd_smp_cpus_pending); |
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wd_smp_last_reset_tb = get_tb(); |
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} |
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wd_smp_unlock(&flags); |
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*this_cpu_ptr(&wd_timer_tb) = get_tb(); |
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hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); |
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hrtimer->function = watchdog_timer_fn; |
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hrtimer_start(hrtimer, ms_to_ktime(wd_timer_period_ms), |
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HRTIMER_MODE_REL_PINNED); |
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} |
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static int start_watchdog_on_cpu(unsigned int cpu) |
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{ |
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return smp_call_function_single(cpu, start_watchdog, NULL, true); |
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} |
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static void stop_watchdog(void *arg) |
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{ |
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struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer); |
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int cpu = smp_processor_id(); |
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unsigned long flags; |
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if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) |
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return; /* Can happen in CPU unplug case */ |
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hrtimer_cancel(hrtimer); |
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wd_smp_lock(&flags); |
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cpumask_clear_cpu(cpu, &wd_cpus_enabled); |
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wd_smp_unlock(&flags); |
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wd_smp_clear_cpu_pending(cpu); |
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} |
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static int stop_watchdog_on_cpu(unsigned int cpu) |
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{ |
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return smp_call_function_single(cpu, stop_watchdog, NULL, true); |
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} |
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static void watchdog_calc_timeouts(void) |
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{ |
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wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq; |
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|
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/* Have the SMP detector trigger a bit later */ |
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wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2; |
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|
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/* 2/5 is the factor that the perf based detector uses */ |
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wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5; |
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} |
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void watchdog_nmi_stop(void) |
|
{ |
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int cpu; |
|
|
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for_each_cpu(cpu, &wd_cpus_enabled) |
|
stop_watchdog_on_cpu(cpu); |
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} |
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|
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void watchdog_nmi_start(void) |
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{ |
|
int cpu; |
|
|
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watchdog_calc_timeouts(); |
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for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) |
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start_watchdog_on_cpu(cpu); |
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} |
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|
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/* |
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* Invoked from core watchdog init. |
|
*/ |
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int __init watchdog_nmi_probe(void) |
|
{ |
|
int err; |
|
|
|
err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, |
|
"powerpc/watchdog:online", |
|
start_watchdog_on_cpu, |
|
stop_watchdog_on_cpu); |
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if (err < 0) { |
|
pr_warn("could not be initialized"); |
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return err; |
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} |
|
return 0; |
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}
|
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|