Let me just say that the user space approach does not work because the
kernel sets the cpumask to all and then spawns a thread f.e. for
usermodehelper.
This mean we would have to run a daemon that keeps scanning for errand
threads and then move them. But at that point the damage would already
have been done. Short term threads would never be caught.
So I think the kernel based approach is unavoidable.
Look at this in kernel/kmod.c:
static int ____call_usermodehelper(void *data)
{
struct subprocess_info *sub_info = data;
struct cred *new;
int retval;
spin_lock_irq(¤t->sighand->siglock);
flush_signal_handlers(current, 1);
spin_unlock_irq(¤t->sighand->siglock);
/* We can run anywhere, unlike our parent keventd(). */
set_cpus_allowed_ptr(current, cpu_all_mask);
!!!!! No chance to catch this from user space.
....
retval = do_execve(sub_info->path,
(const char __user *const __user *)sub_info->argv,
(const char __user *const __user *)sub_info->envp);
if (!retval)
....
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