On Sun, 30 Mar 2008 23:24:50 +0800
"Peter Teoh" <htmldeveloper@xxxxxxxxx> wrote:
> Is there any guidelines on when and where can we insert printk() to do
> debugging?
You can use it pretty much anywhere.
> asmlinkage int vprintk(const char *fmt, va_list args)
> {
...
> preempt_disable();
> /* This stops the holder of console_sem just where we want him */
> raw_local_irq_save(flags);
>
> So we can see that printk() MUST NOT BE USED when the kernel is
> preempt-disabled, as at the end of printk() it will be enabled again.
>
> MISUSE scenario: using printk() INSIDE a spin_lock()-spin_unlock() pair.
Multiple preempt_disable+preempt_enable sequences can nest, because
they simply keep a counter and preemption will not be enabled until
the counter reaches zero (the outer-most preempt_disable call).
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