Questions on Call single data (CSD)

Hi, I have couple of questions on Call single data (CSD) . I am going through kernel/smp.c - From what i understand CSD struct is used to run a particular function on a another core (Not sure if i am right ) ? (csd -> func) ( in function smp_call_function_many) - What do these csd_lock_wait and csd_lock do. As per the code this its used to serialize access and it says there is a per CPU CSD resources. I am not getting what is meant here.If its per CPU , then why serialize access ? - The list inside csd . Is this by any chance circular ? Thanks and regards, Vignesh -- http://vigneshradhakrishnan.blogspot.com/