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 18:56:58 +0200
From:	"Dmitry Kravkov" <dmitry@...adcom.com>
To:	pravin <pravin.shelar@...il.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 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.




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