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>

1 files changed, 31 insertions, 32 deletions

diff --git a/include/net/udplite.h b/include/net/udplite.h
index 673a024c6b2a..5f097ca7d5c5 100644
--- 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);