linux-kernel - Re: [PATCH 1/1] ipc/shm: fix the historical/wrong mm->start

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Message-ID: <20140825190956.GA25759@redhat.com>
Date:	Mon, 25 Aug 2014 21:09:56 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Manfred Spraul <manfred@...orfullife.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Andrew Vagin <avagin@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Julien Tinnes <jln@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ipc/shm: fix the historical/wrong mm->start_stack
	check

On 08/25, Hugh Dickins wrote:
>
> On Mon, 25 Aug 2014, Oleg Nesterov wrote:
> > On 08/25, Hugh Dickins wrote:
> >
> > > And I think I'll let Linus's guard page justify your 4 (to match comment)
> > > in place of the original's mysterious 5.
> >
> > Ah, thanks again. Yes, if we want to guarantee 4 pages we should check 5.
> >
> > Although obviously this doesn't explain the original's 5, this was
> > written before check_stack_guard_page().
>
> I meant, you changed the coded 5 to 4, to match the comment above it;
> and if I were insistent on maximizing back-compatible-safety, I would
> say that 4 should go back to 5;

I already did this ;) I'll send v2 patch in a minute.

> But I didn't understand your "to guarantee 4 we should check 5".

I just tried to say that I fully agree with your point.

I didn't dare to preserve your acks although the patch is almost the
same, I'll appreciate it if you can ack v2 too.

Oleg.

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