sysrq的show-backtrace-all-active-cpus(l) 为啥不打印callstack

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本文链接： https://blog.csdn.net/tiantao2012/article/details/89254542

echo "0" > cat /proc/sys/kernel/sysrq
echo t > /proc/sysrq-trigger
echo l > /proc/sysrq-trigger

在使能sysrq后，通过echo l的方式来当前系统的callstack，发现没有效果，只打印了一行log ，并没有打印callstack
linux-mlfz:/sys/bus/pci/devices # dmesg
[177803.446872] sysrq: SysRq : Show backtrace of all active CPUs

在driver/tty/sysrq.c 中查看l按键对应的处理函数，发现当前cpu 是idle的时候，就不会打印callstack
tatic void sysrq_handle_showallcpus(int key)
{
	/*
	 * Fall back to the workqueue based printing if the
	 * backtrace printing did not succeed or the
	 * architecture has no support for it:
	 */
	if (!trigger_all_cpu_backtrace()) {
		struct pt_regs *regs = NULL;

		if (in_irq())
			regs = get_irq_regs();
		if (regs) {
			pr_info("CPU%d:\n", smp_processor_id());
			show_regs(regs);
		}
#调用work来打印callstack
		schedule_work(&sysrq_showallcpus);
	}
}
sysrq_showallcpus的处理函数如下：
static void sysrq_showregs_othercpus(struct work_struct *dummy)
{
	smp_call_function(showacpu, NULL, 0);
}
继续看showacpu
static void showacpu(void *dummy)
{
	unsigned long flags;
#从这里可以看出当cpu是idle的时候就不会打印callstack
	/* Idle CPUs have no interesting backtrace. */
	if (idle_cpu(smp_processor_id()))
		return;

	spin_lock_irqsave(&show_lock, flags);
	pr_info("CPU%d:\n", smp_processor_id());
	show_stack(NULL, NULL);
	spin_unlock_irqrestore(&show_lock, flags);
}