linux-kernel - Re: [PATCH] taskstats: Use better ifdef for alignment

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Message-Id: <20101230.162328.104050033.davem@davemloft.net>
Date:	Thu, 30 Dec 2010 16:23:28 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	jeffm@...e.com
Cc:	akpm@...ux-foundation.org, error27@...il.com,
	balbir@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] taskstats: Use better ifdef for alignment

From: Jeff Mahoney <jeffm@...e.com>
Date: Wed, 29 Dec 2010 19:12:08 -0500

>  Commit 4be2c95d added a null field to align the taskstats structure but
>  the discussion centered around ia64. The issue exists on other platforms
>  with inefficient unaligned access and adding them piecemeal would be
>  an unmaintainable mess.
> 
>  This patch uses Dave Miller's suggestion of using a combination of
>  CONFIG_64BIT && !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS to determine
>  whether alignment is needed.
> 
>  Note that this will cause breakage on those platforms with applications
>  like iotop which had hard-coded offsets into the packet to access the
>  taskstats structure.
> 
>  The message seen on systems without the alignment fixes looks like:
>  kernel unaligned access to 0xe000023879dca9bc, ip=0xa000000100133d10
> 
>  The addresses may vary but resolve to locations inside __delayacct_add_tsk.
> 
> Reported-by: David S. Miller <davem@...emloft.net>
> Signed-off-by: Jeff Mahoney <jeffm@...e.com>

Acked-by: David S. Miller <davem@...emloft.net>
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