Re: [PATCH net] igc: only strip RX timestamp header from first buffer

["Dahan, AvigailX" <avigailx.dahan@intel.com>]

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On 26/08/2026 2:55, Paul Moses wrote:
> igc_clean_rx_irq() strips IGC_TS_HDR_LEN whenever a descriptor reports
> IGC_RXDADV_STAT_TSIP. For multi-buffer packets, continuation descriptors
> retain TSIP even though the inline timestamp is present only in the first
> RX buffer.
>
> Subtracting the header length from each continuation buffer truncates
> jumbo packets by 16 bytes per continuation and leaves the packet length
> larger than the received data.
>
> Only consume the timestamp header when skb is NULL, which identifies the
> first buffer of a new packet. An skb carried in rx_ring->skb remains
> non-NULL when packet assembly resumes in a later NAPI poll.
>
> Link:https://lore.kernel.org/all/20260625-igb-rx-ts-fix-v3-1-99b3efa08dca@aweta.nl/
> Fixes: e1ed4f92a625 ("igc: Refactor Rx timestamp handling")
> Cc:stable@vger.kernel.org
> Signed-off-by: Paul Moses<p@1g4.org>
> ---
> #
> # REPRO
> #
> # Receiver: igc / enp1s0 / 10.0.5.175
> # Sender:   RTL8125B / enP4p65s0 / 10.0.5.165
>
> # Both hosts
> sudo ip link set dev enp1s0 mtu 9000
> sudo ip link set dev enP4p65s0 mtu 9000
>
> # Baseline: RX timestamping off
> sudo hwstamp_ctl -i enp1s0 -t 0 -r 0
> ping -n -M do -c 5 -s 8972 10.0.5.175
> # 5/5 received
>
> # Enable RX timestamping only
> sudo hwstamp_ctl -i enp1s0 -t 0 -r 1
>
> # Receiver
> sudo timeout 20 tcpdump -ni enp1s0 -s 0 -w /tmp/igc-jumbo.pcap \
>    'icmp and host 10.0.5.165'
>
> # Sender
> ping -n -M do -c 5 -W 2 -s 8972 10.0.5.175
> # 0/5 received
>
> # Receiver
> sudo tcpdump -nn -e -vvv -r /tmp/igc-jumbo.pcap
> # length 8950
> # [total length 9000 > length 8936] (invalid)
> # wrong icmp cksum
>
> # Expected Ethernet length: 9014
> # Captured length:          8950
> # Loss:                       64 = 4 continuation buffers * 16 bytes
>
> # Disable RX timestamping again
> sudo hwstamp_ctl -i enp1s0 -t 0 -r 0
> ping -n -M do -c 5 -s 8972 10.0.5.175
> # 5/5 received
>
> ---
>
>   drivers/net/ethernet/intel/igc/igc_main.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>

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