From: Jason Xing <kerneljasonxing@gmail•com>
To: davem@davemloft•net, edumazet@google•com, kuba@kernel•org,
pabeni@redhat•com, horms@kernel•org, willemb@google•com,
martin.lau@kernel•org
Cc: netdev@vger•kernel.org, bpf@vger•kernel.org,
Jason Xing <kernelxing@tencent•com>,
Yushan Zhou <katrinzhou@tencent•com>
Subject: [PATCH net-next v2 3/4] bpf-timestamp: keep track of the skb when wait_for_space occurs
Date: Sat, 4 Apr 2026 23:04:51 +0800 [thread overview]
Message-ID: <20260404150452.83904-4-kerneljasonxing@gmail.com> (raw)
In-Reply-To: <20260404150452.83904-1-kerneljasonxing@gmail.com>
From: Jason Xing <kernelxing@tencent•com>
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 <katrinzhou@tencent•com>
Signed-off-by: Jason Xing <kernelxing@tencent•com>
---
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
next prev parent reply other threads:[~2026-04-04 15:05 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-04 15:04 [PATCH net-next v2 0/4] bpf-timestamp: convert to push-level granularity Jason Xing
2026-04-04 15:04 ` [PATCH net-next v2 1/4] tcp: separate BPF timestamping from tcp_tx_timestamp Jason Xing
2026-04-04 15:04 ` [PATCH net-next v2 2/4] tcp: advance the tsflags check to save cycles Jason Xing
2026-04-06 2:23 ` Willem de Bruijn
2026-04-06 11:48 ` Jason Xing
2026-04-04 15:04 ` Jason Xing [this message]
2026-04-06 2:28 ` [PATCH net-next v2 3/4] bpf-timestamp: keep track of the skb when wait_for_space occurs Willem de Bruijn
2026-04-06 11:59 ` Jason Xing
2026-04-06 14:37 ` Willem de Bruijn
2026-04-07 3:33 ` Jason Xing
2026-04-07 7:43 ` Jason Xing
2026-04-07 21:17 ` Willem de Bruijn
2026-04-08 0:35 ` Jason Xing
2026-04-08 7:30 ` Jason Xing
2026-04-08 15:15 ` Willem de Bruijn
2026-04-08 18:12 ` Martin KaFai Lau
2026-04-08 23:52 ` Jason Xing
2026-04-08 23:05 ` Jason Xing
2026-04-04 15:04 ` [PATCH net-next v2 4/4] bpf-timestamp: complete tracing the skb from each push in sendmsg Jason Xing
2026-04-06 2:17 ` [PATCH net-next v2 0/4] bpf-timestamp: convert to push-level granularity Willem de Bruijn
2026-04-06 12:25 ` Jason Xing
2026-04-06 14:38 ` Willem de Bruijn
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