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Thu, 18 Jun 2026 17:38:18 +0000 Message-ID: <55ab9b13-ee51-4ac6-af7b-b3feb159eb51@intel.com> Date: Thu, 18 Jun 2026 10:38:15 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] igb: only strip Rx timestamp header on the first buffer of a frame To: Kurt Kanzenbach , Tjerk Kusters , "netdev@vger.kernel.org" CC: "intel-wired-lan@lists.osuosl.org" , "przemyslaw.kitszel@intel.com" , "andrew+netdev@lunn.ch" , "davem@davemloft.net" , "edumazet@google.com" , "kuba@kernel.org" , "pabeni@redhat.com" , "richardcochran@gmail.com" , "hawk@kernel.org" , "stable@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <8733yojljf.fsf@jax.kurt.home> Content-Language: en-US From: Tony Nguyen In-Reply-To: <8733yojljf.fsf@jax.kurt.home> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR03CA0274.namprd03.prod.outlook.com (2603:10b6:303:b5::9) To DS0PR11MB8230.namprd11.prod.outlook.com (2603:10b6:8:158::21) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB8230:EE_|PH7PR11MB8249:EE_ X-MS-Office365-Filtering-Correlation-Id: 6eb7dd23-8c74-44f2-30f3-08decd60620a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|7416014|376014|366016|6133799003|4143699003|11063799006|5023799004|56012099006|18002099003|22082099003; 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apologies for the >> attachment. > > b4 has a web submission endpoint. Maybe you can use that one: > > https://b4.docs.kernel.org/en/latest/contributor/send.html Hi Tjerk, It would be great if you could get this setup as it makes patch handling easier. > [snip] > >> From fee3e3452dfcd7e109332369672a3e0090cadeb3 Mon Sep 17 00:00:00 2001 >> From: T Kusters >> Date: Tue, 9 Jun 2026 14:06:24 +0200 >> Subject: [PATCH net] igb: only strip Rx timestamp header on the first buffer >> of a frame >> >> When Rx hardware timestamping is enabled (e.g. ptp4l, which configures >> HWTSTAMP_FILTER_ALL), the NIC prepends a 16-byte timestamp header to the >> first Rx buffer of every received frame. igb_clean_rx_irq() strips this >> header inside its per-buffer loop: >> >> if (igb_test_staterr(rx_desc, E1000_RXDADV_STAT_TSIP)) { >> ts_hdr_len = igb_ptp_rx_pktstamp(rx_ring->q_vector, >> pktbuf, ×tamp); >> pkt_offset += ts_hdr_len; >> size -= ts_hdr_len; >> } >> >> For a frame that spans more than one Rx buffer (e.g. a jumbo frame), this >> block runs once per buffer. The timestamp header only exists at the start >> of the first buffer, but igb_ptp_rx_pktstamp() is called for every buffer. >> >> On a continuation buffer the data is packet payload, not a timestamp >> header. igb_ptp_rx_pktstamp() already has two guards against acting on a >> non-header buffer: it returns 0 if PTP is disabled, and returns 0 if the >> reserved dwords (the first 8 bytes) are non-zero. Neither is sufficient >> here: PTP is enabled, and a continuation buffer whose payload happens to >> begin with 8 zero bytes passes the reserved-dword check. In that case the >> payload is mistaken for a valid timestamp header and igb_ptp_rx_pktstamp() >> returns IGB_TS_HDR_LEN, so the caller strips 16 bytes of real data from >> that buffer. A frame spanning N buffers whose continuation buffers start >> with zero bytes therefore loses 16 * (N - 1) bytes from its tail. >> >> This is easily triggered by a GigE Vision camera streaming dark frames >> (mostly 0x00 pixel data) over jumbo UDP with PTP active on the receiver: >> the all-zero frames arrive truncated while frames with non-zero content >> are fine. There is no error indication. >> >> No content-based check can reliably tell a continuation buffer that begins >> with zero bytes from a real timestamp header, because both are all zero. >> Fix it structurally instead: only attempt the strip on the first buffer of >> a frame, which is the only buffer that can contain a timestamp header. In >> igb_clean_rx_irq() skb is NULL until the first buffer has been processed, >> so guarding the strip with !skb restricts it to the first buffer >> regardless of payload content. >> >> Fixes: 5379260852b0 ("igb: Fix XDP with PTP enabled") >> Cc: stable@vger.kernel.org >> Signed-off-by: T Kusters Sign off should be your full name. Thanks, Tony > Great explanation! igb_clean_rx_irq_zc() does not need the same > treatment, correct? > > Reviewed-by: Kurt Kanzenbach > >> --- >> drivers/net/ethernet/intel/igb/igb_main.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c >> index ce91dda00ec0..abb55cd589a9 100644 >> --- a/drivers/net/ethernet/intel/igb/igb_main.c >> +++ b/drivers/net/ethernet/intel/igb/igb_main.c >> @@ -9061,7 +9061,8 @@ static int igb_clean_rx_irq(struct igb_q_vector *q_vector, const int budget) >> pktbuf = page_address(rx_buffer->page) + rx_buffer->page_offset; >> >> /* pull rx packet timestamp if available and valid */ >> - if (igb_test_staterr(rx_desc, E1000_RXDADV_STAT_TSIP)) { >> + if (!skb && >> + igb_test_staterr(rx_desc, E1000_RXDADV_STAT_TSIP)) { >> int ts_hdr_len; >> >> ts_hdr_len = igb_ptp_rx_pktstamp(rx_ring->q_vector, >> -- >> 2.27.0 >>