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

[venu]

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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