If you are in a process context (any syscall) and want to lock other process out, use a semaphore. You can take a semaphore and sleep (copy_from_user*( or kmalloc(x,GFP_KERNEL)).

Otherwise (== data can be touched in an interrupt), use spin_lock_irqsave() and spin_unlock_irqrestore().

Avoid holding spinlock for more than 5 lines of code and across any function call (except accessors like readb).