udplite: fast-path computation of checksum coverage

Commit 903ab86d195cca295379699299c5fc10beba31c7 of 1 March this year ("udp: Add
lockless transmit path") introduced a new fast TX path that broke the checksum
coverage computation of UDP-lite, which so far depended on up->len (only set
if the socket is locked and 0 in the fast path).

Fixed by providing both fast- and slow-path computation of checksum coverage.
The latter can be removed when UDP(-lite)v6 also uses a lockless transmit path.

Reported-by: Thomas Volkert <thomas@homer-conferencing.com>
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/udplite.h b/include/net/udplite.h
index 673a024..5f097ca 100644 (file)
--- a/include/net/udplite.h
+++ b/include/net/udplite.h
@@ -66,40 +66,34 @@ static inline int udplite_checksum_init(struct sk_buff *skb, struct udphdr *uh)
        return 0;
 }
 
-static inline int udplite_sender_cscov(struct udp_sock *up, struct udphdr *uh)
+/* Slow-path computation of checksum. Socket is locked. */
+static inline __wsum udplite_csum_outgoing(struct sock *sk, struct sk_buff *skb)
 {
+       const struct udp_sock *up = udp_sk(skb->sk);
        int cscov = up->len;
+       __wsum csum = 0;
 
-       /*
-        * Sender has set `partial coverage' option on UDP-Lite socket
-        */
-       if (up->pcflag & UDPLITE_SEND_CC)    {
+       if (up->pcflag & UDPLITE_SEND_CC) {
+               /*
+                * Sender has set `partial coverage' option on UDP-Lite socket.
+                * The special case "up->pcslen == 0" signifies full coverage.
+                */
                if (up->pcslen < up->len) {
-               /* up->pcslen == 0 means that full coverage is required,
-                * partial coverage only if  0 < up->pcslen < up->len */
-                       if (0 < up->pcslen) {
-                              cscov = up->pcslen;
-                       }
-                       uh->len = htons(up->pcslen);
+                       if (0 < up->pcslen)
+                               cscov = up->pcslen;
+                       udp_hdr(skb)->len = htons(up->pcslen);
                }
-       /*
-        * NOTE: Causes for the error case  `up->pcslen > up->len':
-        *        (i)  Application error (will not be penalized).
-        *       (ii)  Payload too big for send buffer: data is split
-        *             into several packets, each with its own header.
-        *             In this case (e.g. last segment), coverage may
-        *             exceed packet length.
-        *       Since packets with coverage length > packet length are
-        *       illegal, we fall back to the defaults here.
-        */
+               /*
+                * NOTE: Causes for the error case  `up->pcslen > up->len':
+                *        (i)  Application error (will not be penalized).
+                *       (ii)  Payload too big for send buffer: data is split
+                *             into several packets, each with its own header.
+                *             In this case (e.g. last segment), coverage may
+                *             exceed packet length.
+                *       Since packets with coverage length > packet length are
+                *       illegal, we fall back to the defaults here.
+                */
        }
-       return cscov;
-}
-
-static inline __wsum udplite_csum_outgoing(struct sock *sk, struct sk_buff *skb)
-{
-       int cscov = udplite_sender_cscov(udp_sk(sk), udp_hdr(skb));
-       __wsum csum = 0;
 
        skb->ip_summed = CHECKSUM_NONE;     /* no HW support for checksumming */
 
@@ -115,16 +109,21 @@ static inline __wsum udplite_csum_outgoing(struct sock *sk, struct sk_buff *skb)
        return csum;
 }
 
+/* Fast-path computation of checksum. Socket may not be locked. */
 static inline __wsum udplite_csum(struct sk_buff *skb)
 {
-       struct sock *sk = skb->sk;
-       int cscov = udplite_sender_cscov(udp_sk(sk), udp_hdr(skb));
+       const struct udp_sock *up = udp_sk(skb->sk);
        const int off = skb_transport_offset(skb);
-       const int len = skb->len - off;
+       int len = skb->len - off;
 
+       if ((up->pcflag & UDPLITE_SEND_CC) && up->pcslen < len) {
+               if (0 < up->pcslen)
+                       len = up->pcslen;
+               udp_hdr(skb)->len = htons(up->pcslen);
+       }
        skb->ip_summed = CHECKSUM_NONE;     /* no HW support for checksumming */
 
-       return skb_checksum(skb, off, min(cscov, len), 0);
+       return skb_checksum(skb, off, len, 0);
 }
 
 extern void    udplite4_register(void);