Re: kern/57049: large TCP transfers NetBSD-Xen-Guest -> NetBSD-Xen-DOM0 abort with EHOSTDOWN

[Frank Kardel <kardel%netbsd.org@localhost>]

The following reply was made to PR kern/57049; it has been noted by GNATS.

From: Frank Kardel <kardel%netbsd.org@localhost>
To: gnats-bugs%netbsd.org@localhost, kern-bug-people%netbsd.org@localhost,
 gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/57049: large TCP transfers NetBSD-Xen-Guest ->
 NetBSD-Xen-DOM0 abort with EHOSTDOWN
Date: Sat, 19 Nov 2022 16:31:50 +0100

 Yes I think it is somehow related to the new ARP code in nd.c.
 
 New datapoint:
 Reversing the transfer to send from DOM0 to guest survive longer. DOM0 
 is fine. on the guest the EHOSTDOWN return in nd.c:~390 is triggered often.
 As failure of sending ACK does not terminate TCP connections that is why 
 the connection survives.
 The timing pattern seems to be a mixture of 200ms (possible ACK 
 re-sends) and ~41 seconds (possibly the nd.c effect).
 
 The EHOSTDOWN pattern looks like this:
 
 [  2174.429719] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2174.639722] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2217.636882] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2217.841108] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2218.051081] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2218.261120] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2259.258196] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2259.462455] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2259.672445] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2300.669503] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2300.873729] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2301.083775] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2301.293752] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2342.290807] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2342.495060] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2342.705039] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2342.915041] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2383.912120] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2384.116365] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2384.326380] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2384.536361] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2427.533491] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2427.737675] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2427.947745] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2428.157763] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2469.154813] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2469.358585] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 [  2469.568578] /src/NetBSD/999100/src/sys/net/nd.c:391: EHOSTDOWN
 
 Best regards,
    Frank
 On 10/07/22 17:10, Manuel Bouyer wrote:
 > The following reply was made to PR kern/57049; it has been noted by GNATS.
 >
 > From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
 > To: Frank Kardel <kardel%netbsd.org@localhost>
 > Cc: gnats-bugs%netbsd.org@localhost, kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
 >          netbsd-bugs%netbsd.org@localhost
 > Subject: Re: kern/57049: large TCP transfers NetBSD-Xen-Guest ->
 >   NetBSD-Xen-DOM0 abort with EHOSTDOWN
 > Date: Fri, 7 Oct 2022 17:07:37 +0200
 >
 >   On Fri, Oct 07, 2022 at 04:43:52PM +0200, Frank Kardel wrote:
 >   > Hi Manuel,
 >   >
 >   > that is probably because the DOMU is 9.2 which still had the classic ARP
 >   > resolution code. In 9.99.x the ARP resolution
 >   >
 >   > was replaced with a neighbour discovery derived code in nd.c. On Xen I
 >   > tripped over this issue with a 99.100 GENERIC guest quickly. It may be that
 >   > it
 >   >
 >   > happens with other true network peers also, but I was not able to trigger it
 >   > with a true network peer right away.
 >   
 >   OK, with a HEAD domU I can reproduce this.
 >   But I don't think this is Xen-specific. Maybe it's just some timing or
 >   ressource issue that makes it more likely to happen on Xen.
 >   
 >   --
 >   Manuel Bouyer <bouyer%antioche.eu.org@localhost>
 >        NetBSD: 26 ans d'experience feront toujours la difference
 >   --
 >