On Tue, Oct 1, 2019 at 7:36 AM Josh Hunt <joh...@akamai.com> wrote:
>
>
>
> On 9/30/19 4:56 PM, Alexander Duyck wrote:
> > On Mon, Sep 30, 2019 at 3:13 PM Josh Hunt <joh...@akamai.com> wrote:
> >>
> >> Prior to this change an application sending <= 1MSS worth of data and
> >> enabling UDP GSO would fail if the system had SW GSO enabled, but the
> >> same send would succeed if HW GSO offload is enabled. In addition to this
> >> inconsistency the error in the SW GSO case does not get back to the
> >> application if sending out of a real device so the user is unaware of this
> >> failure.
> >>
> >> With this change we only perform GSO if the # of segments is > 1 even
> >> if the application has enabled segmentation. I've also updated the
> >> relevant udpgso selftests.
> >>
> >> Fixes: bec1f6f69736 ("udp: generate gso with UDP_SEGMENT")
> >> Signed-off-by: Josh Hunt <joh...@akamai.com>
> >> ---
> >> net/ipv4/udp.c | 5 +++--
> >> net/ipv6/udp.c | 5 +++--
> >> tools/testing/selftests/net/udpgso.c | 16 ++++------------
> >> 3 files changed, 10 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> >> index be98d0b8f014..ac0baf947560 100644
> >> --- a/net/ipv4/udp.c
> >> +++ b/net/ipv4/udp.c
> >> @@ -821,6 +821,7 @@ static int udp_send_skb(struct sk_buff *skb, struct
> >> flowi4 *fl4,
> >> int is_udplite = IS_UDPLITE(sk);
> >> int offset = skb_transport_offset(skb);
> >> int len = skb->len - offset;
> >> + int datalen = len - sizeof(*uh);
> >> __wsum csum = 0;
> >>
> >> /*
> >> @@ -832,7 +833,7 @@ static int udp_send_skb(struct sk_buff *skb, struct
> >> flowi4 *fl4,
> >> uh->len = htons(len);
> >> uh->check = 0;
> >>
> >> - if (cork->gso_size) {
> >> + if (cork->gso_size && datalen > cork->gso_size) {
> >> const int hlen = skb_network_header_len(skb) +
> >> sizeof(struct udphdr);
> >>
> >
> > So what about the datalen == cork->gso_size case? That would only
> > generate one segment wouldn't it?
> >
> > Shouldn't the test really be "datalen < cork->gso_size"? That should
> > be the only check you need since if gso_size is 0 this statement would
> > always fail anyway.
> >
> > Thanks.
> >
> > - Alex
> >
>
> Alex thanks for the review. The intent of the patch is to only use GSO
> when the # of segs > 1. The two cases you've mentioned are when the # of
> segs == 1. In those cases we don't want to set gso_size and treat this
> as a non-GSO case, skipping the if block. Let me know if I misunderstood
> your points or you'd like further clarification.
>
> Thanks!
> Josh
Your right. Somehow I got the logic backwards in my head.
Thanks.
- Alex
