Re: [RFC PATCH v2 02/10] udp: implement GRO for plain UDP sockets.

[Paolo Abeni <pabeni@redhat.com>]

On Sun, 2018-10-21 at 16:06 -0400, Willem de Bruijn wrote:
> On Fri, Oct 19, 2018 at 10:30 AM Paolo Abeni <pabeni@redhat.com> wrote:
> > 
> > This is the RX counterpart of commit bec1f6f69736 ("udp: generate gso
> > with UDP_SEGMENT"). When UDP_GRO is enabled, such socket is also
> > eligible for GRO in the rx path: UDP segments directed to such socket
> > are assembled into a larger GSO_UDP_L4 packet.
> > 
> > The core UDP GRO support is enabled with setsockopt(UDP_GRO).
> > 
> > Initial benchmark numbers:
> > 
> > Before:
> > udp rx:   1079 MB/s   769065 calls/s
> > 
> > After:
> > udp rx:   1466 MB/s    24877 calls/s
> > 
> > 
> > This change introduces a side effect in respect to UDP tunnels:
> > after a UDP tunnel creation, now the kernel performs a lookup per ingress
> > UDP packet, while before such lookup happened only if the ingress packet
> > carried a valid internal header csum.
> > 
> > v1 -> v2:
> >  - use a new option to enable UDP GRO
> >  - use static keys to protect the UDP GRO socket lookup
> > 
> > Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> > ---
> >  include/linux/udp.h      |   3 +-
> >  include/uapi/linux/udp.h |   1 +
> >  net/ipv4/udp.c           |   7 +++
> >  net/ipv4/udp_offload.c   | 109 +++++++++++++++++++++++++++++++--------
> >  net/ipv6/udp_offload.c   |   6 +--
> >  5 files changed, 98 insertions(+), 28 deletions(-)
> > 
> > diff --git a/include/linux/udp.h b/include/linux/udp.h
> > index a4dafff407fb..f613b329852e 100644
> > --- a/include/linux/udp.h
> > +++ b/include/linux/udp.h
> > @@ -50,11 +50,12 @@ struct udp_sock {
> >         __u8             encap_type;    /* Is this an Encapsulation socket? */
> >         unsigned char    no_check6_tx:1,/* Send zero UDP6 checksums on TX? */
> >                          no_check6_rx:1,/* Allow zero UDP6 checksums on RX? */
> > -                        encap_enabled:1; /* This socket enabled encap
> > +                        encap_enabled:1, /* This socket enabled encap
> >                                            * processing; UDP tunnels and
> >                                            * different encapsulation layer set
> >                                            * this
> >                                            */
> > +                        gro_enabled:1; /* Can accept GRO packets */
> > 
> >         /*
> >          * Following member retains the information to create a UDP header
> >          * when the socket is uncorked.
> > diff --git a/include/uapi/linux/udp.h b/include/uapi/linux/udp.h
> > index 09502de447f5..30baccb6c9c4 100644
> > --- a/include/uapi/linux/udp.h
> > +++ b/include/uapi/linux/udp.h
> > @@ -33,6 +33,7 @@ struct udphdr {
> >  #define UDP_NO_CHECK6_TX 101   /* Disable sending checksum for UDP6X */
> >  #define UDP_NO_CHECK6_RX 102   /* Disable accpeting checksum for UDP6 */
> >  #define UDP_SEGMENT    103     /* Set GSO segmentation size */
> > +#define UDP_GRO                104     /* This socket can receive UDP GRO packets */
> > 
> >  /* UDP encapsulation types */
> >  #define UDP_ENCAP_ESPINUDP_NON_IKE     1 /* draft-ietf-ipsec-nat-t-ike-00/01 */
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 9fcb5374e166..3c277378814f 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -115,6 +115,7 @@
> >  #include "udp_impl.h"
> >  #include <net/sock_reuseport.h>
> >  #include <net/addrconf.h>
> > +#include <net/udp_tunnel.h>
> > 
> >  struct udp_table udp_table __read_mostly;
> >  EXPORT_SYMBOL(udp_table);
> > @@ -2459,6 +2460,12 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
> >                 up->gso_size = val;
> >                 break;
> > 
> > +       case UDP_GRO:
> > +               if (valbool)
> > +                       udp_tunnel_encap_enable(sk->sk_socket);
> > +               up->gro_enabled = valbool;
> 
> The socket lock is not held here, so multiple updates to
> up->gro_enabled and the up->encap_enabled and the static branch can
> race. Syzkaller is adept at generating those.

Good catch. I was fooled by the current existing code. I think there
are potentially similar issues for UDP_ENCAP, UDPLITE_SEND_CSCOV, ...

Since the rx path don't take it anymore and we don't risk starving, I
think we should could/always acquire the socket lock on setsockopt,
wdyt?

> > +#define UDO_GRO_CNT_MAX 64
> > +static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
> > +                                              struct sk_buff *skb)
> > +{
> > +       struct udphdr *uh = udp_hdr(skb);
> > +       struct sk_buff *pp = NULL;
> > +       struct udphdr *uh2;
> > +       struct sk_buff *p;
> > +
> > +       /* requires non zero csum, for simmetry with GSO */
> 
> symmetry

Thanks ;)

Paolo