Subject: Re: Memory corruption due to word sharing
From: Colin Walters <walters@verbum.org>
To: Jan Kara <jack@suse.cz>
Cc: LKML <linux-kernel@vger.kernel.org>, linux-ia64@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>, dsterba@suse.cz,
        ptesarik@suse.cz, rguenther@suse.de, gcc@gcc.gnu.org
Date: Wed, 01 Feb 2012 11:37:45 -0500
In-Reply-To: <20120201151918.GC16714@quack.suse.cz>
References: <20120201151918.GC16714@quack.suse.cz>
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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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