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

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Message-ID: <20090608064148.GA516@in.ibm.com>
Date:	Mon, 8 Jun 2009 12:11:49 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	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>,
	Masami Hiramatsu <mhiramat@...hat.com>
Subject: Re: [PATCH] kmemcheck: move hook before preempt_conditional_sti()

On Sun, Jun 07, 2009 at 06:26:52PM +0200, Vegard Nossum wrote:
> There are actually two problems here:
> 
> 1. We absolutely cannot enable IRQs in case the fault was caused by
>    kmemcheck.
> 
> 2. We cannot enable preemption and then return from the debug handler
>    without disabling preemption afterwards.
> 
> The problem seems to be a merge fallout between three commits:
> 
> commit 3d2a71a596bd9c761c8487a2178e95f8a61da083
> Author: Alexander van Heukelum <heukelum@...tmail.fm>
> Date:   Tue Sep 30 18:41:37 2008 +0200
> 
>     x86, traps: converge do_debug handlers
> 
> commit 08d68323d1f0c34452e614263b212ca556dae47f
> Author: K.Prasad <prasad@...ux.vnet.ibm.com>
> Date:   Mon Jun 1 23:44:08 2009 +0530
> 
>     hw-breakpoints: modifying generic debug exception to use thread-specific deb
> 
> 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.

Ananth
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