// SPDX-License-Identifier: GPL-2.0
  /*
   * Provide a default dump_stack() function for architectures
   * which don't implement their own.
   */
  
  #include <linux/kernel.h>
  #include <linux/export.h>
  #include <linux/sched.h>
  #include <linux/sched/debug.h>
  #include <linux/smp.h>
  #include <linux/atomic.h>
  
  static void __dump_stack(void)
  {
  	dump_stack_print_info(KERN_DEFAULT);
  	show_stack(NULL, NULL);
  }
  
  /**
   * dump_stack - dump the current task information and its stack trace
   *
   * Architectures can override this implementation by implementing its own.
   */
  #ifdef CONFIG_SMP
  static atomic_t dump_lock = ATOMIC_INIT(-1);
  
  asmlinkage __visible void dump_stack(void)
  {
  	unsigned long flags;
  	int was_locked;
  	int old;
  	int cpu;
  
  	/*
  	 * Permit this cpu to perform nested stack dumps while serialising
  	 * against other CPUs
  	 */
  retry:
  	local_irq_save(flags);
  	cpu = smp_processor_id();
  	old = atomic_cmpxchg(&dump_lock, -1, cpu);
  	if (old == -1) {
  		was_locked = 0;
  	} else if (old == cpu) {
  		was_locked = 1;
  	} else {
  		local_irq_restore(flags);
  		cpu_relax();
  		goto retry;
  	}
  
  	__dump_stack();
  
  	if (!was_locked)
  		atomic_set(&dump_lock, -1);
  
  	local_irq_restore(flags);
  }
  #else
  asmlinkage __visible void dump_stack(void)
  {
  	__dump_stack();
  }
  #endif
  EXPORT_SYMBOL(dump_stack);