printk实现疑惑

woshizzb 发表于 2014-07-22 22:22

截取printk的一段实现代码： preempt_disable();
/* This stops the holder of console_sem just where we want him */
raw_local_irq_save(flags);
this_cpu = smp_processor_id();

/*
* Ouch, printk recursed into itself!
*/
if (unlikely(printk_cpu == this_cpu)) {
   /*
      * If a crash is occurring during printk() on this CPU,
      * then try to get the crash message out but make sure
      * we can't deadlock. Otherwise just return to avoid the
      * recursion and return - but flag the recursion so that
      * it can be printed at the next appropriate moment:
      */
   if (!oops_in_progress) {
         recursion_bug = 1;
         goto out_restore_irqs;
   }
   zap_locks();
}
里面有检测printk嵌套的判断。但我比较疑惑这在什么情况下会发生？因为一开始已经禁用了抢占和本地中断，printk如何嵌套？
我尝试了在printk中访问非法内存，可惜串口直接挂死，并未打印出 BUG: recent printk recursion!

amarant 发表于 2014-07-23 08:04

可以直接往串口写东西

hmsghnh 发表于 2014-07-23 13:02

比如pirntk 触发串口写，串口驱动l里面又printk。

humjb_1983 发表于 2014-07-23 19:02

同一个流程中的嵌套，不涉及调度。。。

blake326 发表于 2016-07-12 10:52

1. printk内部发生异常（比如bug或者内存硬件错误，关中断时异常还是可以响应的），bug后续代码又调用到了printk。
2. printk过程中（printk过程中会关中断的）发生fiq，比如有的系统的watchdog中断，后续也可能会调用到printk

页: [1]

Chinaunix's Archiver

printk实现疑惑