All tasks in the process group have the same sid, we don't need to iterate
them all to check that the caller of sys_setpgid() doesn't change its
session.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>