[PATCH net] tcp: inherit timestamp on mtu probe

[PATCH net] tcp: inherit timestamp on mtu probe

[Willem de Bruijn]

From: Willem de Bruijn <willemb@google.com>

TCP associates tx timestamp requests with a byte in the bytestream.
If merging skbs in tcp_mtu_probe, migrate the tstamp request.

Similar to MSG_EOR, do not allow moving a timestamp from any segment
in the probe but the last. This to avoid merging multiple timestamps.

Tested with the packetdrill script at
https://github.com/wdebruij/packetdrill/commits/mtu_probe-1

Link: http://patchwork.ozlabs.org/patch/1143278/#2232897
Fixes: 4ed2d765dfac ("net-timestamp: TCP timestamping")
Signed-off-by: Willem de Bruijn <willemb@google.com>
---
 net/ipv4/tcp_output.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 5c46bc4c7e8d..42abc9bd687a 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2053,7 +2053,7 @@ static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len)
 		if (len <= skb->len)
 			break;
 
-		if (unlikely(TCP_SKB_CB(skb)->eor))
+		if (unlikely(TCP_SKB_CB(skb)->eor) || tcp_has_tx_tstamp(skb))
 			return false;
 
 		len -= skb->len;
@@ -2170,6 +2170,7 @@ static int tcp_mtu_probe(struct sock *sk)
 			 * we need to propagate it to the new skb.
 			 */
 			TCP_SKB_CB(nskb)->eor = TCP_SKB_CB(skb)->eor;
+			tcp_skb_collapse_tstamp(nskb, skb);
 			tcp_unlink_write_queue(skb, sk);
 			sk_wmem_free_skb(sk, skb);
 		} else {
-- 
2.23.0.187.g17f5b7556c-goog

Re: [PATCH net] tcp: inherit timestamp on mtu probe

[Eric Dumazet]

On Tue, Aug 27, 2019 at 9:09 PM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> From: Willem de Bruijn <willemb@google.com>
>
> TCP associates tx timestamp requests with a byte in the bytestream.
> If merging skbs in tcp_mtu_probe, migrate the tstamp request.
>
> Similar to MSG_EOR, do not allow moving a timestamp from any segment
> in the probe but the last. This to avoid merging multiple timestamps.
>
> Tested with the packetdrill script at
> https://github.com/wdebruij/packetdrill/commits/mtu_probe-1
>
> Link: http://patchwork.ozlabs.org/patch/1143278/#2232897
> Fixes: 4ed2d765dfac ("net-timestamp: TCP timestamping")
> Signed-off-by: Willem de Bruijn <willemb@google.com>
> ---
>  net/ipv4/tcp_output.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 5c46bc4c7e8d..42abc9bd687a 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2053,7 +2053,7 @@ static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len)
>                 if (len <= skb->len)
>                         break;
>
> -               if (unlikely(TCP_SKB_CB(skb)->eor))
> +               if (unlikely(TCP_SKB_CB(skb)->eor) || tcp_has_tx_tstamp(skb))
>                         return false;
>
>                 len -= skb->len;
> @@ -2170,6 +2170,7 @@ static int tcp_mtu_probe(struct sock *sk)
>                          * we need to propagate it to the new skb.
>                          */
>                         TCP_SKB_CB(nskb)->eor = TCP_SKB_CB(skb)->eor;
> +                       tcp_skb_collapse_tstamp(nskb, skb);

nit: maybe rename tcp_skb_collapse_tstamp() to tcp_skb_tstamp_copy()
or something ?

Its name came from the fact that it was only used from
tcp_collapse_retrans(), but it will no
longer be the case after your fix.

>                         tcp_unlink_write_queue(skb, sk);
>                         sk_wmem_free_skb(sk, skb);
>                 } else {
> --
> 2.23.0.187.g17f5b7556c-goog
>

Re: [PATCH net] tcp: inherit timestamp on mtu probe

[Willem de Bruijn]

On Tue, Aug 27, 2019 at 4:07 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Tue, Aug 27, 2019 at 9:09 PM Willem de Bruijn
> <willemdebruijn.kernel@gmail.com> wrote:
> >
> > From: Willem de Bruijn <willemb@google.com>
> >
> > TCP associates tx timestamp requests with a byte in the bytestream.
> > If merging skbs in tcp_mtu_probe, migrate the tstamp request.
> >
> > Similar to MSG_EOR, do not allow moving a timestamp from any segment
> > in the probe but the last. This to avoid merging multiple timestamps.
> >
> > Tested with the packetdrill script at
> > https://github.com/wdebruij/packetdrill/commits/mtu_probe-1
> >
> > Link: http://patchwork.ozlabs.org/patch/1143278/#2232897
> > Fixes: 4ed2d765dfac ("net-timestamp: TCP timestamping")
> > Signed-off-by: Willem de Bruijn <willemb@google.com>
> > ---
> >  net/ipv4/tcp_output.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> > index 5c46bc4c7e8d..42abc9bd687a 100644
> > --- a/net/ipv4/tcp_output.c
> > +++ b/net/ipv4/tcp_output.c
> > @@ -2053,7 +2053,7 @@ static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len)
> >                 if (len <= skb->len)
> >                         break;
> >
> > -               if (unlikely(TCP_SKB_CB(skb)->eor))
> > +               if (unlikely(TCP_SKB_CB(skb)->eor) || tcp_has_tx_tstamp(skb))
> >                         return false;
> >
> >                 len -= skb->len;
> > @@ -2170,6 +2170,7 @@ static int tcp_mtu_probe(struct sock *sk)
> >                          * we need to propagate it to the new skb.
> >                          */
> >                         TCP_SKB_CB(nskb)->eor = TCP_SKB_CB(skb)->eor;
> > +                       tcp_skb_collapse_tstamp(nskb, skb);
>
> nit: maybe rename tcp_skb_collapse_tstamp() to tcp_skb_tstamp_copy()
> or something ?
>
> Its name came from the fact that it was only used from
> tcp_collapse_retrans(), but it will no
> longer be the case after your fix.

Sure, that's more descriptive.

One caveat, the function is exposed in a header, so it's a
bit more churn. If you don't mind that, I'll send the v2.

Re: [PATCH net] tcp: inherit timestamp on mtu probe

[Eric Dumazet]

On Tue, Aug 27, 2019 at 10:54 PM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:

> Sure, that's more descriptive.
>
> One caveat, the function is exposed in a header, so it's a
> bit more churn. If you don't mind that, I'll send the v2.

Oh right it is also used from tcp_shifted_skb() after Martin KaFai Lau fix ...

Re: [PATCH net] tcp: inherit timestamp on mtu probe

[Willem de Bruijn]

On Tue, Aug 27, 2019 at 4:58 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Tue, Aug 27, 2019 at 10:54 PM Willem de Bruijn
> <willemdebruijn.kernel@gmail.com> wrote:
>
> > Sure, that's more descriptive.
> >
> > One caveat, the function is exposed in a header, so it's a
> > bit more churn. If you don't mind that, I'll send the v2.
>
> Oh right it is also used from tcp_shifted_skb() after Martin KaFai Lau fix ...

Leave as is then?

Re: [PATCH net] tcp: inherit timestamp on mtu probe

[Eric Dumazet]

On Tue, Aug 27, 2019 at 11:16 PM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> On Tue, Aug 27, 2019 at 4:58 PM Eric Dumazet <edumazet@google.com> wrote:
> >
> > On Tue, Aug 27, 2019 at 10:54 PM Willem de Bruijn
> > <willemdebruijn.kernel@gmail.com> wrote:
> >
> > > Sure, that's more descriptive.
> > >
> > > One caveat, the function is exposed in a header, so it's a
> > > bit more churn. If you don't mind that, I'll send the v2.
> >
> > Oh right it is also used from tcp_shifted_skb() after Martin KaFai Lau fix ...
>
> Leave as is then?

Not a big deal really ;)

Signed-off-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH net] tcp: inherit timestamp on mtu probe

[David Miller]

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: Tue, 27 Aug 2019 15:09:33 -0400

> From: Willem de Bruijn <willemb@google.com>
> 
> TCP associates tx timestamp requests with a byte in the bytestream.
> If merging skbs in tcp_mtu_probe, migrate the tstamp request.
> 
> Similar to MSG_EOR, do not allow moving a timestamp from any segment
> in the probe but the last. This to avoid merging multiple timestamps.
> 
> Tested with the packetdrill script at
> https://github.com/wdebruij/packetdrill/commits/mtu_probe-1
> 
> Link: http://patchwork.ozlabs.org/patch/1143278/#2232897
> Fixes: 4ed2d765dfac ("net-timestamp: TCP timestamping")
> Signed-off-by: Willem de Bruijn <willemb@google.com>

Applied and queued up for -stable.