centos man page for sys_tgkill

SYS_TGKILL(9)							   Driver Basics						     SYS_TGKILL(9)

NAME
       sys_tgkill - send signal to one specific thread

SYNOPSIS
       long sys_tgkill(pid_t tgid, pid_t pid, int sig);

ARGUMENTS
       tgid
	   the thread group ID of the thread

       pid
	   the PID of the thread

       sig
	   signal to be sent

DESCRIPTION
       This syscall also checks the tgid and returns -ESRCH even if the PID exists but it's not belonging to the target process anymore. This
       method solves the problem of threads exiting and PIDs getting reused.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							     SYS_TGKILL(9)