I still can't use sys_rt_sigprocmask. Yes it is recognize by the compiler when I included linux/syscalls.h, because when I try to put wrong arguments, it givess an error. But when I load the module to the kernel, it says undefined symbol 'sys_rt_sigprocmask'. Also I noticed that the two arguments are supposed to be user space variables (because of the __user). So this means that I still need to do some copy_from_user routines just to get the values for these arguments from the user space? Thanks!