netdev - Re: [PATCH net-next v2 1/2] ip_gre: allow CSUM capable devices to handle packets

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Date:	Sun, 24 Feb 2013 22:09:14 -0800
From:	Pravin Shelar <pshelar@...ira.com>
To:	Dmitry Kravkov <dmitry@...adcom.com>
Cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 1/2] ip_gre: allow CSUM capable devices to
 handle packets

On Sun, Feb 24, 2013 at 8:56 AM, Dmitry Kravkov <dmitry@...adcom.com> wrote:
> On Thu, 2013-02-21 at 23:19 -0800, pravin wrote:
>> On Thu, Feb 21, 2013 at 3:46 PM, pravin <pravin.shelar@...il.com> wrote:
>> > On Thu, Feb 21, 2013 at 2:26 PM, Dmitry Kravkov <dmitry@...adcom.com> wrote:
>> >> On Tue, 2013-02-19 at 15:03 -0800, pravin wrote:
>> >>> On Tue, Feb 19, 2013 at 11:20 AM, Dmitry Kravkov <dmitry@...adcom.com> wrote:
>> >>> >
>> >>> >> -----Original Message-----
>> >>> >> From: pravin [mailto:pravin.shelar@...il.com]
>> >>> >> Sent: Tuesday, February 19, 2013 8:28 PM
>> >>> >> To: Dmitry Kravkov
>> >>> >> Cc: davem@...emloft.net; netdev@...r.kernel.org
>> >>> >> Subject: Re: [PATCH net-next v2 1/2] ip_gre: allow CSUM capable devices to
>> >>> >> handle packets
>> >>> >>
>> >>> >> On Mon, Feb 18, 2013 at 11:50 AM, Dmitry Kravkov <dmitry@...adcom.com>
>> >>> >> wrote:
>> >>> >> > If device is not able to handle checksumming it will
>> >>> >> > be handled in dev_xmit
>> >>> >> >
>> >>> >> > Signed-off-by: Dmitry Kravkov <dmitry@...adcom.com>
>> >>> >> > ---
>> >>> >> > Changes from v1: fixed email address
>> >>> >> >
>> >>> >> >  net/ipv4/ip_gre.c |    7 ++-----
>> >>> >> >  1 files changed, 2 insertions(+), 5 deletions(-)
>> >>> >> >
>> >>> >> > diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
>> >>> >> > index a56f118..cdc31ac 100644
>> >>> >> > --- a/net/ipv4/ip_gre.c
>> >>> >> > +++ b/net/ipv4/ip_gre.c
>> >>> >> > @@ -745,12 +745,9 @@ static struct sk_buff *handle_offloads(struct sk_buff
>> >>> >> *skb)
>> >>> >> >                         goto error;
>> >>> >> >                 skb_shinfo(skb)->gso_type |= SKB_GSO_GRE;
>> >>> >> >                 return skb;
>> >>> >> > -       } else if (skb->ip_summed == CHECKSUM_PARTIAL) {
>> >>> >> > -               err = skb_checksum_help(skb);
>> >>> >> > -               if (unlikely(err))
>> >>> >> > -                       goto error;
>> >>> >> >         }
>> >>> >> > -       skb->ip_summed = CHECKSUM_NONE;
>> >>> >> > +       if (skb->ip_summed != CHECKSUM_PARTIAL)
>> >>> >> > +               skb->ip_summed = CHECKSUM_NONE;
>> >>> >> >
>> >>> >> >         return skb;
>> >>> >> >
>> >>> >> > --
>> >>> >> > 1.7.7.2
>> >>> >> >
>> >>> >> >
>> >>> >>
>> >>> >> This patch breaks GRE tunnel with GRE_CSUM. since GRE_CSUM need
>> >>> >> complete IP packet to checksum entire GRE payload.
>> >>> >
>> >>> > Testing for o_flags&GRE_CSUM does not look too hurt here, since it will be used in ipgre_tunnel_xmit() later on
>> >>> > This is the only problematic case, right?
>> >>> >
>> >>>
>> >>> It does not work for me. I have GRE device with csum on. Ping works
>> >>> fine but Netperf is not working.
>> >>> Looking at code, I am not sure how tcp will work if inner packet TCP
>> >>> checksum is calculated after GRE_CSUM calculation.
>> >>
>> >>
>> >> Fixes handling when CSUM or SEQ flags are set - via skb_checksum_help()
>> >> ---
>> >> Tested with each mode (separately)
>> >>
>> >>  net/ipv4/ip_gre.c |   14 +++++++++++---
>> >>  1 files changed, 11 insertions(+), 3 deletions(-)
>> >>
>> >> diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
>> >> index 5ef4da7..0de54cd 100644
>> >> --- a/net/ipv4/ip_gre.c
>> >> +++ b/net/ipv4/ip_gre.c
>> >> @@ -735,7 +735,8 @@ drop:
>> >>         return 0;
>> >>  }
>> >>
>> >> -static struct sk_buff *handle_offloads(struct sk_buff *skb)
>> >> +static struct sk_buff *handle_offloads(struct ip_tunnel *tunnel,
>> >> +                                      struct sk_buff *skb)
>> >>  {
>> >>         int err;
>> >>
>> >> @@ -745,8 +746,15 @@ static struct sk_buff *handle_offloads(struct
>> >> sk_buff *skb)
>> >>                         goto error;
>> >>                 skb_shinfo(skb)->gso_type |= SKB_GSO_GRE;
>> >>                 return skb;
>> >> +       } else if (tunnel->parms.o_flags&(GRE_SEQ|GRE_CSUM) &&
>> >> +                  skb->ip_summed == CHECKSUM_PARTIAL) {
>> >> +               err = skb_checksum_help(skb);
>> >> +               if (unlikely(err))
>> >> +                       goto error;
>> >>         }
>>
>> one more thing, there is no need to do csum for GRE_SEQ case.
> If csum is not performed TCP csum become incorrect for offload
> capable and incapable devices.
>
>
that csum computation is only required for GRE_CSUM case, not for GRE_SEQ.
I have send out patches to fix GRE issues, please have a look.

>
>
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