linux-kernel - Re: [PATCH] kmemcheck: move hook before preempt_conditional

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Date:	Mon, 08 Jun 2009 15:46:20 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	ananth@...ibm.com, Vegard Nossum <vegard.nossum@...il.com>
CC:	linux-kernel@...r.kernel.org,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH] kmemcheck: move hook before preempt_conditional_sti()

Ananth N Mavinakayanahalli wrote:
> On Sun, Jun 07, 2009 at 06:26:52PM +0200, Vegard Nossum wrote:
>> commit 787ecfaa503dc63ff1831ddc74b15dad49bace1d
>> Author: Vegard Nossum <vegard.nossum@...il.com>
>> Date:   Fri Apr 4 00:53:23 2008 +0200
>>
>>     x86: add hooks for kmemcheck
>>
>> I encourage the kprobe developers to check whether their code is correct
>> as it stands in current tip/master. Also, comments on this particular
>> change is welcome.
> 
> I see no problem with this change wrt kprobes, since the changes happen
> after the notify_die, by which time, kprobes would've returned
> NOTIFY_DONE since the per-cpu current_kprobe == NULL.

BTW, what will happen if kmemchecked page is accessed from
kprobe's single-stepping instruction? :-)

If a pagefault occurs before (kprobe's)single-step is done,
may kmemcheck's single-step handler be ignored by kprobe's
single-step handler? If it's true, I think kmemcheck hook
should be done before notify_die. (and add __kprobes to some
kmemcheck functions)

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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