netdev - Re: [PATCH] openvswitch: fix sw_flow

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Date:	Fri, 30 Aug 2013 11:22:11 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	Andy Zhou <azhou@...ira.com>
Cc:	David Miller <davem@...emloft.net>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] openvswitch: fix sw_flow_key alignment

On Fri, Aug 30, 2013 at 10:32 AM, Andy Zhou <azhou@...ira.com> wrote:
> diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
> index ad1aeeb..fe7524c4 100644
> --- a/net/openvswitch/flow.c
> +++ b/net/openvswitch/flow.c
>  int ovs_flow_init(void)
>  {
>         BUILD_BUG_ON(sizeof(struct sw_flow_key) % sizeof(long));
> +       BUILD_BUG_ON(sizeof(struct sw_flow_key) % __alignof__(long));

Should this be checking alignof struct sw_flow_key instead of the size?

>         flow_cache = kmem_cache_create("sw_flow", sizeof(struct sw_flow), 0,
>                                         0, NULL);
> diff --git a/net/openvswitch/flow.h b/net/openvswitch/flow.h
> index b65f885..202c4c4 100644
> --- a/net/openvswitch/flow.h
> +++ b/net/openvswitch/flow.h
> @@ -125,7 +125,7 @@ struct sw_flow_key {
>                         } nd;
>                 } ipv6;
>         };
> -} __aligned(__alignof__(long));
> +} __aligned(sizeof(long));

This is going to result in the alignment issue discussed yesterday
where on 32-bit machines the 64 bit members potentially become
misaligned. The suggestion that Geert made was to just drop this
entirely and rely on the natural alignment from these values.
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