linux hangs with printk on schedule()

[Haoqiang Zheng]

I found Linux hangs when printk is inserted to the function schedule().
Sure, it doesn't make much sense to add such a line to schedule(). But Linux
shouldn't hang anyway, right? It's assumed that printk can be inserted
safely to anywhere. So, is it a bug of Linux?

The linux I am running is 2.4.18-14, the same version used by Redhat 8.0.
The scheduler is Ingo's O(1) scheduler.

Here is a fragment of the code
****************************************************************
 switch (prev->state) {
     ------
     default:
            printk("deactivating task pid=%d
comm=%s\n",prev->pid,prev->comm);
             deactivate_task(prev, rq);
  }
******************************************************************