What is the significance of __releases & __acquires in rpm_callback() of power/runtime.c ?

While going thro? run time power management code in K39
power/runtime.c file, am seeing a function definition as given below. Any idea,
what ?__releases? & ?__acquires? are doing in this function definition? 
?
static int rpm_callback(int (*cb)(struct device *), struct
device *dev)
??????????????? __releases(&dev->power.lock)
__acquires(&dev->power.lock)
{
??????????????? int
retval;
??????????????? ?.
??????????????? return
retval;
}
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