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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);
}