linux-kernel - Re: [PATCH 1/2] mm/vmalloc: export is_vmalloc_or_module

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Message-ID: <CA+55aFzzxcrLrUaCrzFbwS_74B2iHd3OvQ=WC-DR-rqpOA0j0A@mail.gmail.com>
Date:	Sat, 8 Feb 2014 14:24:42 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Richard Yao <ryao@...too.org>
Cc:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Eric Van Hensbergen <ericvh@...il.com>,
	Ron Minnich <rminnich@...dia.gov>,
	Latchesar Ionkov <lucho@...kov.net>,
	"David S. Miller" <davem@...emloft.net>,
	V9FS Develooper Mailing List 
	<v9fs-developer@...ts.sourceforge.net>,
	Linux Netdev Mailing List <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Will Deacon <will.deacon@....com>,
	Christopher Covington <cov@...eaurora.org>,
	Matthew Thode <mthode@...ode.org>
Subject: Re: [PATCH 1/2] mm/vmalloc: export is_vmalloc_or_module_addr

On Sat, Feb 8, 2014 at 12:44 PM, Richard Yao <ryao@...too.org> wrote:
>
> However, is_vmalloc_addr() only applies to the vmalloc region. While all
> architectures load kernel modules into virtual memory (to my knowledge),
> some architectures do not load them into the vmalloc region.

So?

People shouldn't do IO to module data, so who cares if something is a
module address or not?

The thing is, even module *loading* doesn't do IO to the magic module
addresses - it loads the module data into regular vmalloc space, and
then copies it into the final location separately.

And no module should ever do any IO on random static data (and
certainly not on code).

So there is _zero_ reason for a driver or a filesystem to use
is_vmalloc_or_module_addr(). It's just not a valid question to ask.

If somebody uses module data/code addresses, we're *better* off with a
oops or other nasty behavior than to try to make it "work".

            Linus
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