For UP system
#protect share data
spin_lock/spin_unlock: protect the data during process context(and only at process context), and make sure your code bewteen lock/unlock is fast enough.There may deadlock if the same spin_lock is called at interrupt context.
spin_lock_irq/spin_unlock_irq: call it during interrupt context, make sure the irq is on before calling this function, it will disable irq before accessing share data
spin_lock_irqsave/irqrestore: use at interrupt context, and will save/restort irq registers
The code between spin_lock**/spin_unlock** must not sleep.
The spin_lock** API is defined at include/linux/spinlock_api_up.h for UP architecture.
linux/kernel/spinlock.c is only for SMP.
mutex_lock/mutex_unlock: the similar with down/up, but more efficient
mutex_lock_interruptible: the simlilar with down_interruptiable, can be interruptiable by signal.(like CTRL-C)
the code beween mutex_lock and mutex_unlock can go to sleep
