printk 会引起调用 schedule 吗？

Question

小弟今天看 LDD3 的第 548 页，有一段

...这包含任何可能调用 schedule 的函数，比如常见的 copy_to_user/kmalloc/printk...

以前看到很多讨论都是说 printk 可以用在中断上下文的，刚才也去看了一下代码，printk 在进入 vprintk 也关了中断

preempt_disable();
/* This stops the holder of console_sem just where we want him */
raw_local_irq_save(flags);

是不是书说错了？

Answer 1

还一个疑问，为什么进入 printk 要延时？

1. boot_delay_msec();
2. printk_delay();

Answer 2

应该是书上错了吧。

/**
* printk - print a kernel message
* @fmt: format string
*
* This is printk(). It can be called from any context. We want it to work.
* Be aware of the fact that if oops_in_progress is not set, we might try to
* wake klogd up which could deadlock on runqueue lock if printk() is called
* from scheduler code.
*
* We try to grab the console_sem. If we succeed, it's easy - we log the output and
* call the console drivers. If we fail to get the semaphore we place the output
* into the log buffer and return. The current holder of the console_sem will
* notice the new output in release_console_sem() and will send it to the
* consoles before releasing the semaphore.
*
* One effect of this deferred printing is that code which calls printk() and
* then changes console_loglevel may break. This is because console_loglevel
* is inspected when the actual printing occurs.
*
* See also:
* printf(3)
*/