Re: [PATCH] taskstats: Use better ifdef for alignment

Andrew Morton
2010-12-30T00:15:06Z

On Wed, 29 Dec 2010 19:12:08 -0500 Jeff Mahoney <jeffm@suse.com> wrote:

> 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.

That seems a very good reason to not apply the patch.

Tell us more, please...

> 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@davemloft.net>
> Signed-off-by: Jeff Mahoney <jeffm@suse.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
>