[PATCH net 5/5] tcp: add tcp_ooo_try_coalesce() helper

[Eric Dumazet]

In case skb in out_or_order_queue is the result of
multiple skbs coalescing, we would like to get a proper gso_segs
counter tracking, so that future tcp_drop() can report an accurate
number.

I chose to not implement this tracking for skbs in receive queue,
since they are not dropped, unless socket is disconnected.

Signed-off-by: Eric Dumazet <eduma...@google.com>
Acked-by: Soheil Hassas Yeganeh <soh...@google.com>
Acked-by: Yuchung Cheng <ych...@google.com>
---
 net/ipv4/tcp_input.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 
b062a76922384f6199563af7cf30a30c5baa7601..3bcd30a2ba06827e061d86ba22680986824e3ee4
 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4358,6 +4358,23 @@ static bool tcp_try_coalesce(struct sock *sk,
        return true;
 }
 
+static bool tcp_ooo_try_coalesce(struct sock *sk,
+                            struct sk_buff *to,
+                            struct sk_buff *from,
+                            bool *fragstolen)
+{
+       bool res = tcp_try_coalesce(sk, to, from, fragstolen);
+
+       /* In case tcp_drop() is called later, update to->gso_segs */
+       if (res) {
+               u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
+                              max_t(u16, 1, skb_shinfo(from)->gso_segs);
+
+               skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
+       }
+       return res;
+}
+
 static void tcp_drop(struct sock *sk, struct sk_buff *skb)
 {
        sk_drops_add(sk, skb);
@@ -4481,8 +4498,8 @@ static void tcp_data_queue_ofo(struct sock *sk, struct 
sk_buff *skb)
        /* In the typical case, we are adding an skb to the end of the list.
         * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
         */
-       if (tcp_try_coalesce(sk, tp->ooo_last_skb,
-                            skb, &fragstolen)) {
+       if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
+                                skb, &fragstolen)) {
 coalesce_done:
                tcp_grow_window(sk, skb);
                kfree_skb_partial(skb, fragstolen);
@@ -4532,8 +4549,8 @@ static void tcp_data_queue_ofo(struct sock *sk, struct 
sk_buff *skb)
                                tcp_drop(sk, skb1);
                                goto merge_right;
                        }
-               } else if (tcp_try_coalesce(sk, skb1,
-                                           skb, &fragstolen)) {
+               } else if (tcp_ooo_try_coalesce(sk, skb1,
+                                               skb, &fragstolen)) {
                        goto coalesce_done;
                }
                p = &parent->rb_right;
-- 
2.18.0.233.g985f88cf7e-goog