// SPDX-License-Identifier: GPL-2.0
  /*
   *  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.
  		 */
  		put_cpu();
  		return;
  	}
  
  	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)))
  		nmi_cpu_backtrace(NULL);
  
  	if (!cpumask_empty(to_cpumask(backtrace_mask))) {
  		pr_info("Sending NMI from CPU %d to CPUs %*pbl:
  ",
  			this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
  		raise(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)))
  			break;
  		mdelay(1);
  		touch_softlockup_watchdog();
  	}
  
  	/*
  	 * Force flush any remote buffers that might be stuck in IRQ context
  	 * and therefore could not run their irq_work.
  	 */
  	printk_safe_flush();
  
  	clear_bit_unlock(0, &backtrace_flag);
  	put_cpu();
  }
  
  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
  ",
  				cpu, instruction_pointer(regs));
  		} else {
  			pr_warn("NMI backtrace for cpu %d
  ", cpu);
  			if (regs)
  				show_regs(regs);
  			else
  				dump_stack();
  		}
  		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
  		return true;
  	}
  
  	return false;
  }
  NOKPROBE_SYMBOL(nmi_cpu_backtrace);
  #endif