[PATCH net-next v2 4/4] bpf-timestamp: complete tracing the skb from each push in sendmsg

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

The patch is the 2/2 part of push-level granularity feature.

Prior to the patch, BPF timestamping cannot cover this case.
Here is how we reproduce in theory:
1) in the first round, __tcp_push_pending_frames() or tcp_push() kicks
   the stack to transfer the skb.
2) in the second round, problems like skb_copy_to_page_nocache() that
   returns with err code.
3) it jumps into 'do_error" label and then 'out' label.
4) at this point, there is no single skb staying in the write queue
5) the end of sendmsg

Monitor these two push functions with the previous one to complete
the conversion from send-level granularity to push-level granularity.

Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
 net/ipv4/tcp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 7d030a11d004..43fa8329a5ad 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1392,9 +1392,12 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 
 		if (forced_push(tp)) {
 			tcp_mark_push(tp, skb);
+			tcp_bpf_tx_timestamp(sk);
 			__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_PUSH);
-		} else if (skb == tcp_send_head(sk))
+		} else if (skb == tcp_send_head(sk)) {
+			tcp_bpf_tx_timestamp(sk);
 			tcp_push_one(sk, mss_now);
+		}
 		continue;
 
 wait_for_space:
-- 
2.41.3