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Thu, 17 Sep 2026 06:27:50 -0700 (PDT) Received: from KERNELXING-MB0.tencent.com ([114.253.38.195]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2dd89f34921sm26873345ad.84.2026.09.17.06.27.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Sep 2026 06:27:49 -0700 (PDT) From: Jason Xing To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, willemb@google.com, kuniyu@google.com Cc: netdev@vger.kernel.org, Jason Xing Subject: [PATCH net v2] tcp: preserve timestamps across receive queue collapse Date: Thu, 17 Sep 2026 21:27:42 +0800 Message-Id: <20260917132742.87117-1-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When tcp_collapse() rebuilds skbs under memory pressure, the copy process doesn't include the right tstamp and hwtstamp from the old skb. And memcpy(nskb->cb, skb->cb, ...) copies has_rxtstamp, but nskb->tstamp and hwtstamps are left at zero, so tcp_recv_timestamp() ends up emitting no cmsg at all. In net timestamping case, if such an skb happens to be the last one consumed in a recvmsg() call, the application receives no RX timestamp for that call. Fix this by copying both tstamp and hwtstamp to the new skb right after the initialization. Fixes: 98aaa913b4ed ("tcp: Extend SOF_TIMESTAMPING_RX_SOFTWARE to TCP recvmsg") Signed-off-by: Jason Xing --- V2 Link: https://lore.kernel.org/all/20260916124153.43457-1-kerneljasonxing@gmail.com/ 1. add one sentence in commit log from Eric's reply 2. use the same semantic as tcp_add_backlog which is to sync the last skb (Eric) --- net/ipv4/tcp_input.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 0f60a1dbf927..81d587654d3d 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5854,6 +5854,12 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root, if (skb_copy_bits(skb, offset, skb_put(nskb, size), size)) BUG(); TCP_SKB_CB(nskb)->end_seq += size; + if (TCP_SKB_CB(skb)->has_rxtstamp) { + TCP_SKB_CB(nskb)->has_rxtstamp = true; + nskb->tstamp = skb->tstamp; + skb_hwtstamps(nskb)->hwtstamp = + skb_hwtstamps(skb)->hwtstamp; + } copy -= size; start += size; } -- 2.43.5