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 <jesus.sanchez-palen...@intel.com>
> ---
> 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.
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.
