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

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Date:	Wed, 29 Dec 2010 19:12:08 -0500
From:	Jeff Mahoney <jeffm@...e.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Dan Carpenter <error27@...il.com>, balbir@...ux.vnet.ibm.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] taskstats: Use better ifdef for alignment

 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>
---
 kernel/taskstats.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -349,7 +349,7 @@ static int parse(struct nlattr *na, stru
 	return ret;
 }

-#ifdef CONFIG_IA64
+#if defined(CONFIG_64BIT) && !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
 #define TASKSTATS_NEEDS_PADDING 1
 #endif

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