linux-kernel - Re: Memory corruption due to word sharing

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Message-ID: <1328114266.5355.44.camel@lenny>
Date:	Wed, 01 Feb 2012 11:37:45 -0500
From:	Colin Walters <walters@...bum.org>
To:	Jan Kara <jack@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-ia64@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	dsterba@...e.cz, ptesarik@...e.cz, rguenther@...e.de,
	gcc@....gnu.org
Subject: Re: Memory corruption due to word sharing

On Wed, 2012-02-01 at 16:19 +0100, Jan Kara wrote:

> I've raised the issue with our GCC guys and they said to me that: "C does
> not provide such guarantee, nor can you reliably lock different
> structure fields with different locks if they share naturally aligned
> word-size memory regions.  The C++11 memory model would guarantee this,
> but that's not implemented nor do you build the kernel with a C++11
> compiler."

That's interesting.  So it seems like there are two solutions:

1) Use the same lock for a given bitfield
2) Split up the bitfield into different words


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