quoted

local_irq_save();
  some_function();
      rt_spin_lock() --> this calls __might_sleep
local_irq_restore(); --> In this case there's a bug right?

Yes, that's a bug. And that's why you'll see a lot of updates in the
-rt patch with things like: local_irq_save_nort(). And this is also the
cause of some of the #ifdef CONFIG_PREEMPT_RT_FULL. And what makes this
change so challenging ;-)

That clarifies my question. Thanks.