tcp: coalesce/collapse must respect MPTCP extensions

Coalesce and collapse of packets carrying MPTCP extensions is allowed
when the newer packet has no extension or the extensions carried by both
packets are equal.

This allows merging of TSO packet trains and even cross-TSO packets, and
does not require any additional action when moving data into existing
SKBs.

v3 -> v4:
 - allow collapsing, under mptcp_skb_can_collapse() constraint

v5 -> v6:
 - clarify MPTCP skb extensions must always be cleared at allocation
   time

Co-developed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 326043c29c0a1e9b401a4fe33928b006c966c2af..0573ae75c3db3d4104e0212e140d95e6c715945c 100644 (file)
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -8,6 +8,7 @@
 #ifndef __NET_MPTCP_H
 #define __NET_MPTCP_H
 
+#include <linux/skbuff.h>
 #include <linux/types.h>
 
 /* MPTCP sk_buff extension data */
@@ -25,4 +26,60 @@ struct mptcp_ext {
        /* one byte hole */
 };
 
+#ifdef CONFIG_MPTCP
+
+/* move the skb extension owership, with the assumption that 'to' is
+ * newly allocated
+ */
+static inline void mptcp_skb_ext_move(struct sk_buff *to,
+                                     struct sk_buff *from)
+{
+       if (!skb_ext_exist(from, SKB_EXT_MPTCP))
+               return;
+
+       if (WARN_ON_ONCE(to->active_extensions))
+               skb_ext_put(to);
+
+       to->active_extensions = from->active_extensions;
+       to->extensions = from->extensions;
+       from->active_extensions = 0;
+}
+
+static inline bool mptcp_ext_matches(const struct mptcp_ext *to_ext,
+                                    const struct mptcp_ext *from_ext)
+{
+       /* MPTCP always clears the ext when adding it to the skb, so
+        * holes do not bother us here
+        */
+       return !from_ext ||
+              (to_ext && from_ext &&
+               !memcmp(from_ext, to_ext, sizeof(struct mptcp_ext)));
+}
+
+/* check if skbs can be collapsed.
+ * MPTCP collapse is allowed if neither @to or @from carry an mptcp data
+ * mapping, or if the extension of @to is the same as @from.
+ * Collapsing is not possible if @to lacks an extension, but @from carries one.
+ */
+static inline bool mptcp_skb_can_collapse(const struct sk_buff *to,
+                                         const struct sk_buff *from)
+{
+       return mptcp_ext_matches(skb_ext_find(to, SKB_EXT_MPTCP),
+                                skb_ext_find(from, SKB_EXT_MPTCP));
+}
+
+#else
+
+static inline void mptcp_skb_ext_move(struct sk_buff *to,
+                                     const struct sk_buff *from)
+{
+}
+
+static inline bool mptcp_skb_can_collapse(const struct sk_buff *to,
+                                         const struct sk_buff *from)
+{
+       return true;
+}
+
+#endif /* CONFIG_MPTCP */
 #endif /* __NET_MPTCP_H */

diff --git a/include/net/tcp.h b/include/net/tcp.h
index ac52633e7061281b84ad3411a82e382dfe114455..13bc83fab454492c128e18da85cb436badd723a6 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -39,6 +39,7 @@
 #include <net/tcp_states.h>
 #include <net/inet_ecn.h>
 #include <net/dst.h>
+#include <net/mptcp.h>
 
 #include <linux/seq_file.h>
 #include <linux/memcontrol.h>
@@ -978,6 +979,13 @@ static inline bool tcp_skb_can_collapse_to(const struct sk_buff *skb)
        return likely(!TCP_SKB_CB(skb)->eor);
 }
 
+static inline bool tcp_skb_can_collapse(const struct sk_buff *to,
+                                       const struct sk_buff *from)
+{
+       return likely(tcp_skb_can_collapse_to(to) &&
+                     mptcp_skb_can_collapse(to, from));
+}
+
 /* Events passed to congestion control interface */
 enum tcp_ca_event {
        CA_EVENT_TX_START,      /* first transmit when no packets in flight */

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 062b696a5fa15a635cd5d05f0731181760a0b6d9..2914fdf1d543a2bc31d4529a52b6269f0c546502 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1422,7 +1422,7 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
        if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
                goto fallback;
 
-       if (!tcp_skb_can_collapse_to(prev))
+       if (!tcp_skb_can_collapse(prev, skb))
                goto fallback;
 
        in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
@@ -4423,6 +4423,9 @@ static bool tcp_try_coalesce(struct sock *sk,
        if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
                return false;
 
+       if (!mptcp_skb_can_collapse(to, from))
+               return false;
+
 #ifdef CONFIG_TLS_DEVICE
        if (from->decrypted != to->decrypted)
                return false;
@@ -4932,7 +4935,7 @@ restart:
                /* The first skb to collapse is:
                 * - not SYN/FIN and
                 * - bloated or contains data before "start" or
-                *   overlaps to the next one.
+                *   overlaps to the next one and mptcp allow collapsing.
                 */
                if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
                    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
@@ -4941,7 +4944,7 @@ restart:
                        break;
                }
 
-               if (n && n != tail &&
+               if (n && n != tail && mptcp_skb_can_collapse(skb, n) &&
                    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
                        end_of_skbs = false;
                        break;
@@ -4974,6 +4977,7 @@ restart:
                else
                        __skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
                skb_set_owner_r(nskb, sk);
+               mptcp_skb_ext_move(nskb, skb);
 
                /* Copy data, releasing collapsed skbs. */
                while (copy > 0) {
@@ -4993,6 +4997,7 @@ restart:
                                skb = tcp_collapse_one(sk, skb, list, root);
                                if (!skb ||
                                    skb == tail ||
+                                   !mptcp_skb_can_collapse(nskb, skb) ||
                                    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
                                        goto end;
 #ifdef CONFIG_TLS_DEVICE

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 58c92a7d671c54564479db061dcec186a8a7bb34..3ce7fe1c4076e27ed73a34f0a70101f3f5254ab4 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2865,7 +2865,7 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
                if (!tcp_can_collapse(sk, skb))
                        break;
 
-               if (!tcp_skb_can_collapse_to(to))
+               if (!tcp_skb_can_collapse(to, skb))
                        break;
 
                space -= skb->len;