linux-kernel - Re: + fully-honor-vdso_enabled.patch added to -mm tree

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Date:	Mon, 5 Mar 2007 19:56:29 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	John Reiser <jreiser@...Wagon.com>, Andi Kleen <ak@...e.de>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: + fully-honor-vdso_enabled.patch added to -mm tree

On Mon, Mar 05, 2007 at 01:54:44PM +0300, Oleg Nesterov wrote:
> On 03/05, Paul Mundt wrote:
> > -	if (current->binfmt->hasvdso)
> > +	if (current->binfmt->hasvdso && current->mm->context.vdso)
> 
> I think this is correct, but a bit strange.
> 
> The "->context.vdso != NULL" check relies on the fact that .vdso == NULL
> after mm_alloc (because arch_setup_additional_pages() doesn' initialize
> it when vdso_enabled == 0, and it has to be != NULL otherwise).
> 
> This means that binfmt->hasvdso in essence is not used, at least for i386.
> Isn't it better to kill ->hasvdso and just use ->context.vdso ? Every usage
> of ->hasvdso should also check ->context.vdso anyway.
> 
That was my thought as well, it looks like it's only needed for x86_64. We
don't look at binfmt->hasvdso on SH at all at least, and it works fine
there.. I left it in in the patch since I figured x86 had a reason for
checking it, but perhaps someone who knows the x86/x86_64 interaction
can comment on this.
-
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