linux-kernel - Re: [patch 16/17] Immediate Values

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Date:	Sat, 12 Apr 2008 01:06:52 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	Adrian Bunk <bunk@...sta.de>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Christoph Hellwig <hch@...radead.org>, akpm@...l.org
Subject: Re: [patch 16/17] Immediate Values - Documentation

On Friday 11 April 2008 11:16:47 Mathieu Desnoyers wrote:
> * Rusty Russell (rusty@...tcorp.com.au) wrote:
> > On Thursday 10 April 2008 01:08:45 Mathieu Desnoyers wrote:
> > > If you have to read the immediate values from a function declared as
> > > __init or __exit, you should explicitly use _imv_read(), which will
> > > fall back on a global variable read. Failing to do so will leave a
> > > reference to the __init section after it is freed (it would generate a
> > > modpost warning).
> >
> > That's a real usability wart.  Couldn't we skip these in the patching
> > loop if required and revert so noone can make this mistake?
>
> Yeah, I know :(
>
> Well, only if we can find a way to detect the macro is put within a init
> or exit section. Is there some assembly trickery that would permit us to
> do that ?
>
> Otherwise, given the memory freed from the init section could be reused
> later by the kernel, I don't see how we can detect the pointer leads to
> a freed init section and, say, a module.

In theory although not in practice, since everyone vmallocs modules.  Let's 
not rely on that tho.

How about we sweep the immediate table on init discard and remove/mark all the 
init and exit references?

Cheers,
Rusty.
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