linux-kernel - Re: [PATCHv2] kmmio/mmiotrace: fix double free of kmmio_fault

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Date:	Mon, 14 Jun 2010 00:18:03 +0200
From:	Marcin Slusarz <marcin.slusarz@...il.com>
To:	x86@...nel.org
Cc:	LKML <linux-kernel@...r.kernel.org>, Pekka Paalanen <pq@....fi>,
	Stuart Bennett <stuart@...edesktop.org>,
	Marcin Kościelnicki <koriakin@...4.net>,
	Shinpei KATO <shinpei@...is.s.u-tokyo.ac.jp>,
	nouveau@...ts.freedesktop.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCHv2] kmmio/mmiotrace: fix double free of kmmio_fault_pages

On Sun, Jun 13, 2010 at 11:56:54PM +0200, Marcin Slusarz wrote:
> After every iounmap mmiotrace has to free kmmio_fault_pages, but it
> can't do it directly, so it defers freeing by RCU.
> 
> It usually works, but when mmiotraced code calls ioremap-iounmap
> multiple times without sleeping between (so RCU won't kick in and
> start freeing) it can be given the same virtual address, so at
> every iounmap mmiotrace will schedule the same pages for release.
> Obviously it will explode on second free.
> 
> Fix it by marking kmmio_fault_pages which are scheduled for release
> and not adding them second time.
> 
> Signed-off-by: Marcin Slusarz <marcin.slusarz@...il.com>
> Acked-by: Pekka Paalanen <pq@....fi>
> Cc: Stuart Bennett <stuart@...edesktop.org>
> Tested-by: Marcin Kościelnicki <koriakin@...4.net>
> Tested-by: Shinpei KATO <shinpei@...is.s.u-tokyo.ac.jp>
> ---

It would be good to apply it to -stable too. Sometimes people has to test
some earlier kernels because of unfixable constraints (you know, these
uncooperative vendors not releasing their binary drivers for latest kernels)

Marcin
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