linux-kernel - Re: Getting rid of dynamic TASK

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Message-ID: <CALCETrU4me1X7oTriLgFQpTqwaebMsT5sdYZzjC=_EERXNbqzA@mail.gmail.com>
Date:	Tue, 10 May 2016 13:29:50 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Dmitry Safonov <0x7f454c46@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, X86 ML <x86@...nel.org>,
	Ruslan Kabatsayev <b7.10110111@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Getting rid of dynamic TASK_SIZE (on x86, at least)

On May 10, 2016 11:21 AM, "Oleg Nesterov" <oleg@...hat.com> wrote:
>
> On 05/10, Andy Lutomirski wrote:
> >
> >  - xol_add_vma: This one is weird: uprobes really is doing something
> > behind the task's back, and the addresses need to be consistent with
> > the address width.  I'm not quite sure what to do here.
>
> It can use mm->task_size instead, plus this is just a hint. And perhaps
> mm->task_size should have more users, say get_unmapped_area...

Ick.  I hadn't noticed mm->task_size.  We have a *lot* of different
indicators of task size.  mm->task_size appears to have basically no
useful uses except maybe for ppc.

On x86, bitness can change without telling the kernel, and tasks
running in 64-bit mode can do 32-bit syscalls.

So maybe I should add mm->task_size to my list of things that would be
nice to remove.  Or maybe I'm just tilting at windmills.

>
> Not sure we should really get rid of dynamic TASK_SIZE completely, but
> personally I agree it looks a bit ugly.
>
> Oleg.
>