linux-kernel - Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

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Message-ID: <20160627103625.GF31799@dhcp22.suse.cz>
Date:	Mon, 27 Jun 2016 12:36:25 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Andy Lutomirski <luto@...nel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Nadav Amit <nadav.amit@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jann Horn <jann@...jh.net>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86,
 core)

On Fri 24-06-16 22:22:55, Oleg Nesterov wrote:
> On 06/24, Michal Hocko wrote:
> >
> > On Fri 24-06-16 16:05:58, Michal Hocko wrote:
> > > On Thu 23-06-16 20:52:21, Oleg Nesterov wrote:
> > > >
> > > > But I agree, this is fixable (and in fact I still hope TIF_MEMDIE will die,
> > > > at least in its current form).
> > >
> > > We can move the flag to the task_struct.
> 
> Well, I actually meant that to me its usage doesn't look really
> right and we need to change this logic. But this is off-topic.
> 
> > Here is the patch.
> 
> Can't comment, but note that it was decided to move ti->flags into
> task_struct, so the patch is "off-topic" too ;)

OK, my original understanding was that we want to get rid of all the
current thread flags.

> 
> > @@ -1856,6 +1856,8 @@ struct task_struct {
> >  	unsigned long	task_state_change;
> >  #endif
> >  	int pagefault_disabled;
> > +	/* oom victim - give it access to memory reserves */
> > +	atomic_t	memdie;
> 
> Yet another oom member. And these atomic_add_unless's look a bit
> strange, it seems that you could add "bool memdie" and use xchg()
> with the same effect?

That would work as well of course.

Thanks!
-- 
Michal Hocko
SUSE Labs