From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jesus Sanchez-Palencia Subject: Re: [PATCH v2 net-next 01/14] net: Clear skb->tstamp only on the forwarding path Date: Mon, 16 Jul 2018 14:52:48 -0700 Message-ID: References: <20180703224300.25300-1-jesus.sanchez-palencia@intel.com> <20180703224300.25300-2-jesus.sanchez-palencia@intel.com> <1e52c128-59f4-43ae-3487-059a84ae61c3@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: tglx@linutronix.de, jan.altenberg@linutronix.de, vinicius.gomes@intel.com, kurt.kanzenbach@linutronix.de, henrik@austad.us, richardcochran@gmail.com, ilias.apalodimas@linaro.org, ivan.khoronzhuk@linaro.org, mlichvar@redhat.com, willemb@google.com, jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us, jeffrey.t.kirsher@intel.com To: Eric Dumazet , netdev@vger.kernel.org Return-path: Received: from mga02.intel.com ([134.134.136.20]:63254 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728522AbeGPW1W (ORCPT ); Mon, 16 Jul 2018 18:27:22 -0400 In-Reply-To: <1e52c128-59f4-43ae-3487-059a84ae61c3@gmail.com> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: Hi Eric, On 07/13/2018 10:35 AM, Eric Dumazet wrote: > > > On 07/03/2018 03:42 PM, Jesus Sanchez-Palencia wrote: >> This is done in preparation for the upcoming time based transmission >> patchset. Now that skb->tstamp will be used to hold packet's txtime, >> we must ensure that it is being cleared when traversing namespaces. >> Also, doing that from skb_scrub_packet() before the early return would >> break our feature when tunnels are used. >> >> Signed-off-by: Jesus Sanchez-Palencia >> --- >> net/core/skbuff.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/net/core/skbuff.c b/net/core/skbuff.c >> index 1357f36c8a5e..c4e24ac27464 100644 >> --- a/net/core/skbuff.c >> +++ b/net/core/skbuff.c >> @@ -4898,7 +4898,6 @@ EXPORT_SYMBOL(skb_try_coalesce); >> */ >> void skb_scrub_packet(struct sk_buff *skb, bool xnet) >> { >> - skb->tstamp = 0; >> skb->pkt_type = PACKET_HOST; >> skb->skb_iif = 0; >> skb->ignore_df = 0; >> @@ -4912,6 +4911,7 @@ void skb_scrub_packet(struct sk_buff *skb, bool xnet) >> >> ipvs_reset(skb); >> skb->mark = 0; >> + skb->tstamp = 0; >> } >> EXPORT_SYMBOL_GPL(skb_scrub_packet); >> >> > > > > I believe we had some misunderstanding here. > > What I meant by forwarding is the following case : > > - We receive a packet. > - netstamp_wanted is >0 (because at least one packet capture is active) > - __net_timestamp() is called and does : > skb->tstamp = ktime_get_real(); > > Then this skb is forwarded into an interface where EDT is taken into > consideration by either a qdisc or a device. > > Since CLOCK_TAI is a different base than CLOCK_REALTIME, we might have a problem. I'm not sure we have a problem here. For the Tx path I only see net_timestamp_set() being called from dev_queue_xmit_nit(). And even there, it's a clone of the skb that gets timestamped. I believe the original skb, which had the valid txtime copied into skb->tstamp, is not modified anywhere along that path. What am I missing, please? Thanks, Jesus > > > Solutions for this problem : > > 1) Convert all our skb->tstamp usages to CLOCK_TAI base. > > or > > 2) clear skb->tstamp in forwarding paths, including the ones not scrubbing the packet. > > My preference is 1), even if it is a bit more work. >