Some question about "security context of a task"

hi all: I found there is a user_struct, user, located at struct cred. is it possible be null? My platform sometimes panic when using kernel_thread to creating a thread for running. below is the place it happen if (atomic_read(&p->real_cred->user->processes) >= p->signal->rlim[RLIMIT_NPROC].rlim_cur) { after checking the parameter, I found p->real_cred->user is NULL. When and how we allocate/destroy this parameter? Does that mean we should some basic check before calling kernel_thread? -- Regards,