Re: [RFC][PATCH] s390: add arch_change_pid for arch updates after task pid change

[Oleg Nesterov <oleg@redhat.com>]

On 04/19, Martin Schwidefsky wrote:
>
> In a multi-threaded program any thread can call execve(). If this
> is not done by the thread group leader, the de_thread() function
> replaces the pid of the task that calls execve() with the pid of
> thread group leader. If the task reaches user space again without
> going over __switch_to() the sampling tag is still set to the old
> pid.

If this is the only reason for arch_change_pid() hook, then perhaps
it would be better/simpler to add it into de_thread() right after
change_pid(tsk, PIDTYPE_PID, task_pid(leader)) ?

note also that this way arch_change_pid() doesn't need any checks and
any arguments, you can simply do

void arch_change_pid(void)
{
	S390_lowcore.current_pid = current->pid;
	if (test_facility(40))
		lpp(&S390_lowcore.lpp);
}

Oleg.