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 *  NMI backtrace support
 * Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
 * with the following header:
 *  HW NMI watchdog support
 *  started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
 *  Arch specific calls to support NMI watchdog
 *  Bits copied from original nmi.c file
#include <linux/cpumask.h>
#include <linux/delay.h>
#include <linux/kprobes.h>
#include <linux/nmi.h>
#include <linux/cpu.h>
#include <linux/sched/debug.h>

#ifdef arch_trigger_cpumask_backtrace
/* For reliability, we're prepared to waste bits here. */
static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;

/* "in progress" flag of arch_trigger_cpumask_backtrace */
static unsigned long backtrace_flag;

 * When raise() is called it will be passed a pointer to the
 * backtrace_mask. Architectures that call nmi_cpu_backtrace()
 * directly from their raise() functions may rely on the mask
 * they are passed being updated as a side effect of this call.
void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
				   bool exclude_self,
				   void (*raise)(cpumask_t *mask))
	int i, this_cpu = get_cpu();

	if (test_and_set_bit(0, &backtrace_flag)) {
		 * If there is already a trigger_all_cpu_backtrace() in progress
		 * (backtrace_flag == 1), don't output double cpu dump infos.

	cpumask_copy(to_cpumask(backtrace_mask), mask);
	if (exclude_self)
		cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));

	 * Don't try to send an NMI to this cpu; it may work on some
	 * architectures, but on others it may not, and we'll get
	 * information at least as useful just by doing a dump_stack() here.
	 * Note that nmi_cpu_backtrace(NULL) will clear the cpu bit.
	if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask)))

	if (!cpumask_empty(to_cpumask(backtrace_mask))) {
		pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
			this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));

	/* Wait for up to 10 seconds for all CPUs to do the backtrace */
	for (i = 0; i < 10 * 1000; i++) {
		if (cpumask_empty(to_cpumask(backtrace_mask)))

	 * Force flush any remote buffers that might be stuck in IRQ context
	 * and therefore could not run their irq_work.

	clear_bit_unlock(0, &backtrace_flag);

bool nmi_cpu_backtrace(struct pt_regs *regs)
	int cpu = smp_processor_id();

	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
		if (regs && cpu_in_idle(instruction_pointer(regs))) {
			pr_warn("NMI backtrace for cpu %d skipped: idling at pc %#lx\n",
				cpu, instruction_pointer(regs));
		} else {
			pr_warn("NMI backtrace for cpu %d\n", cpu);
			if (regs)
		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
		return true;

	return false;