linux-kernel - Re: [1/2] 2.6.22-rc5: known regressions with patches

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Message-ID: <5640c7e00706201602g5c983a34qf7644b19d6295d42@mail.gmail.com>
Date:	Thu, 21 Jun 2007 11:02:42 +1200
From:	"Ian McDonald" <ian.mcdonald@...di.co.nz>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Miklos Szeredi" <miklos@...redi.hu>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Darrick J. Wong" <djwong@...ibm.com>, "Andi Kleen" <ak@...e.de>,
	"Bj?rn Steinbrink" <B.Steinbrink@....de>,
	"William Cohen" <wcohen@...hat.com>,
	"S. P. Prasanna" <prasanna@...ibm.com>,
	"Antonino Daplas" <adaplas@...il.com>,
	"Olaf Hering" <olaf@...fle.de>, "Ville Syrj?l?" <syrjala@....fi>,
	"Jean Delvare" <khali@...ux-fr.org>,
	"Rudolf Marek" <r.marek@...embler.cz>,
	"Soeren Sonnenburg" <kernel@....de>,
	"Michal Piotrowski" <michal.k.k.piotrowski@...il.com>
Subject: Re: [1/2] 2.6.22-rc5: known regressions with patches

On 6/21/07, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> And yes, sometimes debugging *does* change what it debugs. In timing, if
> nothing else, but also in the kinds of things you can do.

Totally agree.

> For example, we
> don't allow slab redzoning on data structures that have alignment
> restrictions not compatible with the redzoning, and I'd argue that this is
> more of the same: we just should not do DEBUG_RODATA if you expect to
> change read-only data.
>

Well the description for DEBUG_RODATA is:
         Mark the kernel read-only data as write-protected in the pagetables,
         in order to catch accidental (and incorrect) writes to such const data.

What we are doing with kprobes is neither accidental, nor incorrect.

> There's just no *point*.
>
>                 Linus
>
I understand your philosophical viewpoint here. Anyway it's no biggie
as can keep the patch out of tree if I want it... Another option is to
be able to enable and disable protecting read only data via a sysctl
but that seems even uglier.

Anyway I'll stop wasting your time now.

Ian
-- 
Web: http://wand.net.nz/~iam4/
Blog: http://iansblog.jandi.co.nz
WAND Network Research Group
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