From: Jason Xing The patch is the 1/2 part of push-level granularity feature. Tag the skb in tcp_sendmsg_locked() when wait_for_space occurs even though it might not carry the last byte of the sendmsg. Prior to the patch, BPF timestamping cannot cover this case: The following steps reproduce this: 1) skb A is the current last skb before entering wait_for_space process 2) tcp_push() pushes A without any tag 3) A is transmitted from TCP to driver without putting any skb carrying timestamps in the error queue, like SCHED, DRV/HARDWARE. 4) sk_stream_wait_memory() sleeps for a while and then returns with an error code. Note that the socket lock is released. 5) skb A finally gets acked and removed from the rtx queue. 6) continue with the rest of tcp_sendmsg_locked(): it will jump to(goto) 'do_error' label and then 'out' label. 7) at this moment, skb A turns out to be the last one in this send syscall, and miss the following tcp_bpf_tx_timestamp() opportunity before the final tcp_push() 8) BPF script fails to see any timestamps this time Signed-off-by: Yushan Zhou Signed-off-by: Jason Xing --- net/ipv4/tcp.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index c603b90057f6..7d030a11d004 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1400,9 +1400,11 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) wait_for_space: set_bit(SOCK_NOSPACE, &sk->sk_socket->flags); tcp_remove_empty_skb(sk); - if (copied) + if (copied) { + tcp_bpf_tx_timestamp(sk); tcp_push(sk, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH, size_goal); + } err = sk_stream_wait_memory(sk, &timeo); if (err != 0) -- 2.41.3