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Message-ID: <20260106142838.69ecc00c@kernel.org>
Date: Tue, 6 Jan 2026 14:28:38 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Paolo Abeni
<pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Florian Westphal
<fw@...len.de>, netdev@...r.kernel.org, eric.dumazet@...il.com,
syzbot+6023ea32e206eef7920a@...kaller.appspotmail.com, Mazin Al Haddad
<mazin@...state.dev>
Subject: Re: [PATCH v2 net] ip6_gre: use skb_vlan_inet_prepare() instead of
pskb_inet_may_pull()
On Tue, 6 Jan 2026 22:33:05 +0100 Eric Dumazet wrote:
> > [hi on] edumazet@...mazet1:~/git/net-next$ vng -r --user root --cpus
> > 4 --memory 4G
> > /usr/lib/tmpfiles.d/legacy.conf:14: Duplicate line for path
> > "/run/lock", ignoring.
> > _ _
> > __ _(_)_ __| |_ _ __ ___ ___ _ __ __ _
> > \ \ / / | __| __| _ _ \ / _ \_____| _ \ / _ |
> > \ V /| | | | |_| | | | | | __/_____| | | | (_| |
> > \_/ |_|_| \__|_| |_| |_|\___| |_| |_|\__ |
> > |___/
> > kernel version: 6.16.12-1rodete2-amd64 x86_64
> > (CTRL+d to exit)
> >
> > Illegal instruction shell-history-configtool configure-interactively
> > root@...tme-ng:/usr/local/google/home/edumazet/git/net-next# cd
> > tools/testing/selftests/net/
> > root@...tme-ng:/usr/local/google/home/edumazet/git/net-next/tools/testing/selftests/net#
> > ./gre_gso.sh
> > TEST: GREv6/v4 - copy file w/ TSO [ OK ]
> > TEST: GREv6/v4 - copy file w/ GSO [ OK ]
> > 2026/01/06 21:25:27 socat[1214] W exiting on signal 15
> > TEST: GREv6/v6 - copy file w/ TSO [ OK ]
> > TEST: GREv6/v6 - copy file w/ GSO [ OK ]
> > 2026/01/06 21:25:27 socat[1229] W exiting on signal 15
> >
> > Tests passed: 4
> > Tests failed: 0
> > root@...tme-ng:/usr/local/google/home/edumazet/git/net-next/tools/testing/selftests/net#
>
> Ah of course my script had '-r arch/x86/boot/bzImage'
Maybe your machine / TCP tunings are super fast. I think we have some
packet loss here which slows things down, maybe we run into the timeout
of 1 sec with GSO and you don't.
I did this to the (GSO side of the) test:
diff --git a/tools/testing/selftests/net/gre_gso.sh b/tools/testing/selftests/net/gre_gso.sh
index 5100d90f92d2..b9a223b584f6 100755
--- a/tools/testing/selftests/net/gre_gso.sh
+++ b/tools/testing/selftests/net/gre_gso.sh
@@ -125,9 +125,16 @@ gre_gst_test_checks()
ethtool -K veth0 tso off
- cat $TMPFILE | timeout 1 socat -u STDIN TCP:$addr:$port
- log_test $? 0 "$name - copy file w/ GSO"
-
+ $NS_EXEC nstat >>/dev/null
+ nstat >>/dev/null
+ cat $TMPFILE | \time timeout 1 socat -u STDIN TCP:$addr:$port
+ R=$?
+ echo "== Sender"
+ nstat
+ echo "== Receiver"
+ $NS_EXEC nstat
+ log_test $R 0 "$name - copy file w/ GSO"
+
ethtool -K veth0 tso on
kill $PID
Without the fix under discussion I get:
# ./gre_gso.sh
TEST: GREv6/v4 - copy file w/ TSO [ OK ]
0.00user 0.12system 0:00.13elapsed 92%CPU (0avgtext+0avgdata 3744maxresident)k
0inputs+0outputs (0major+406minor)pagefaults 0swaps
== Sender
#kernel
IpInReceives 255 0.0
IpInDelivers 255 0.0
IpOutRequests 259 0.0
IpOutTransmits 259 0.0
TcpActiveOpens 1 0.0
TcpInSegs 255 0.0
TcpOutSegs 1539 0.0
Ip6InReceives 255 0.0
Ip6InDelivers 255 0.0
Ip6InOctets 26528 0.0
Ip6OutOctets 2124096 0.0
Ip6InNoECTPkts 255 0.0
Ip6OutTransmits 259 0.0
TcpExtTCPPureAcks 252 0.0
TcpExtTCPBacklogCoalesce 1 0.0
TcpExtTCPOrigDataSent 1536 0.0
TcpExtTCPDelivered 1537 0.0
IpExtInOctets 13268 0.0
IpExtOutOctets 2110628 0.0
IpExtInNoECTPkts 255 0.0
== Receiver
#kernel
IpInReceives 7 0.0
IpInDelivers 7 0.0
TcpPassiveOpens 2 0.0
TcpInSegs 7 0.0
Ip6InReceives 1287 0.0
Ip6InDelivers 1287 0.0
Ip6InMcastPkts 1 0.0
Ip6InOctets 4328152 0.0
Ip6InMcastOctets 72 0.0
Ip6InNoECTPkts 2564 0.0
Icmp6InNeighborSolicits 1 0.0
Icmp6OutNeighborAdvertisements 1 0.0
Icmp6InType135 1 0.0
Icmp6OutType136 1 0.0
TcpExtTW 2 0.0
TcpExtTCPRcvCoalesce 22 0.0
IpExtInOctets 4194668 0.0
IpExtInNoECTPkts 2564 0.0
TEST: GREv6/v4 - copy file w/ GSO [ OK ]
2026/01/06 17:23:10 socat[787] W exiting on signal 15
TEST: GREv6/v6 - copy file w/ TSO [ OK ]
0.00user 0.12system 0:00.14elapsed 85%CPU (0avgtext+0avgdata 3668maxresident)k
0inputs+0outputs (0major+405minor)pagefaults 0swaps
== Sender
#kernel
TcpActiveOpens 1 0.0
TcpInSegs 261 0.0
TcpOutSegs 1539 0.0
Ip6InReceives 522 0.0
Ip6InDelivers 522 0.0
Ip6OutRequests 263 0.0
Ip6InOctets 51172 0.0
Ip6OutOctets 4245868 0.0
Ip6InNoECTPkts 522 0.0
Ip6OutTransmits 526 0.0
TcpExtTCPPureAcks 257 0.0
TcpExtTCPLossProbes 1 0.0
TcpExtTCPBacklogCoalesce 2 0.0
TcpExtTCPOrigDataSent 1537 0.0
TcpExtTCPDelivered 1538 0.0
== Receiver
#kernel
IpInReceives 7 0.0
IpInDelivers 7 0.0
TcpPassiveOpens 4 0.0
TcpInSegs 11 0.0
Ip6InReceives 2571 0.0
Ip6InDelivers 2571 0.0
Ip6InMcastPkts 1 0.0
Ip6InOctets 12875768 0.0
Ip6InMcastOctets 72 0.0
Ip6InNoECTPkts 7670 0.0
Icmp6InNeighborSolicits 1 0.0
Icmp6OutNeighborAdvertisements 1 0.0
Icmp6InType135 1 0.0
Icmp6OutType136 1 0.0
TcpExtTW 4 0.0
TcpExtTCPRcvCoalesce 42 0.0
IpExtInOctets 4194668 0.0
IpExtInNoECTPkts 2564 0.0
TEST: GREv6/v6 - copy file w/ GSO [ OK ]
2026/01/06 17:23:10 socat[808] W exiting on signal 15
Tests passed: 4
Tests failed: 0
With the change I see retransmits:
# ./gre_gso.sh
TEST: GREv6/v4 - copy file w/ TSO [ OK ]
2026/01/06 17:25:21 socat[805] W exiting on signal 15
Command exited with non-zero status 124
0.00user 0.03system 0:01.02elapsed 3%CPU (0avgtext+0avgdata 3792maxresident)k
0inputs+0outputs (2major+408minor)pagefaults 0swaps
== Sender
#kernel
IpInReceives 103 0.0
IpInDelivers 103 0.0
IpOutRequests 145 0.0
IpOutTransmits 145 0.0
TcpActiveOpens 1 0.0
TcpInSegs 103 0.0
TcpOutSegs 123 0.0
TcpRetransSegs 52 0.0
Ip6InReceives 103 0.0
Ip6InDelivers 103 0.0
Ip6InOctets 11176 0.0
Ip6OutOctets 254280 0.0
Ip6InNoECTPkts 103 0.0
Ip6OutTransmits 145 0.0
TcpExtDelayedACKs 1 0.0
TcpExtTCPPureAcks 88 0.0
TcpExtTCPSackRecovery 9 0.0
TcpExtTCPLostRetransmit 10 0.0
TcpExtTCPLossFailures 1 0.0
TcpExtTCPFastRetrans 33 0.0
TcpExtTCPSlowStartRetrans 15 0.0
TcpExtTCPTimeouts 4 0.0
TcpExtTCPLossProbes 2 0.0
TcpExtTCPSackRecoveryFail 3 0.0
TcpExtTCPBacklogCoalesce 12 0.0
TcpExtTCPSackMerged 4 0.0
TcpExtTCPSackShiftFallback 9 0.0
TcpExtTCPOrigDataSent 120 0.0
TcpExtTCPDelivered 119 0.0
TcpExtTcpTimeoutRehash 4 0.0
IpExtInOctets 5820 0.0
IpExtOutOctets 246740 0.0
IpExtInNoECTPkts 103 0.0
== Receiver
#kernel
IpInReceives 23 0.0
IpInDelivers 22 0.0
TcpPassiveOpens 2 0.0
TcpInSegs 23 0.0
Ip6InReceives 21 0.0
Ip6InDelivers 21 0.0
Ip6InMcastPkts 1 0.0
Ip6InOctets 2262688 0.0
Ip6InMcastOctets 72 0.0
Ip6InNoECTPkts 1295 0.0
Icmp6InNeighborSolicits 1 0.0
Icmp6OutNeighborAdvertisements 1 0.0
Icmp6InType135 1 0.0
Icmp6OutType136 1 0.0
TcpExtTW 1 0.0
TcpExtTCPRcvCoalesce 72 0.0
TcpExtTCPOFOQueue 13 0.0
IpExtInOctets 2261596 0.0
IpExtInNoECTPkts 1295 0.0
TEST: GREv6/v4 - copy file w/ GSO [FAIL]
2026/01/06 17:25:21 socat[789] W exiting on signal 15
TEST: GREv6/v6 - copy file w/ TSO [ OK ]
2026/01/06 17:25:22 socat[825] W exiting on signal 15
Command exited with non-zero status 124
0.00user 0.10system 0:01.05elapsed 9%CPU (0avgtext+0avgdata 3720maxresident)k
0inputs+0outputs (0major+406minor)pagefaults 0swaps
== Sender
#kernel
TcpActiveOpens 1 0.0
TcpInSegs 408 0.0
TcpOutSegs 430 0.0
TcpRetransSegs 73 0.0
Ip6InReceives 818 0.0
Ip6InDelivers 817 0.0
Ip6OutRequests 464 0.0
Ip6InMcastPkts 1 0.0
Ip6OutMcastPkts 1 0.0
Ip6InOctets 81620 0.0
Ip6OutOctets 1460624 0.0
Ip6InMcastOctets 72 0.0
Ip6OutMcastOctets 72 0.0
Ip6InNoECTPkts 818 0.0
Ip6OutTransmits 928 0.0
Icmp6OutMsgs 1 0.0
Icmp6OutRouterSolicits 1 0.0
Icmp6OutType133 1 0.0
TcpExtDelayedACKs 1 0.0
TcpExtTCPPureAcks 238 0.0
TcpExtTCPSackRecovery 15 0.0
TcpExtTCPDSACKUndo 1 0.0
TcpExtTCPLostRetransmit 10 0.0
TcpExtTCPLossFailures 1 0.0
TcpExtTCPFastRetrans 57 0.0
TcpExtTCPSlowStartRetrans 12 0.0
TcpExtTCPTimeouts 4 0.0
TcpExtTCPLossProbes 8 0.0
TcpExtTCPSackRecoveryFail 3 0.0
TcpExtTCPBacklogCoalesce 161 0.0
TcpExtTCPDSACKRecv 1 0.0
TcpExtTCPSackShiftFallback 15 0.0
TcpExtTCPOrigDataSent 427 0.0
TcpExtTCPDelivered 427 0.0
TcpExtTcpTimeoutRehash 4 0.0
TcpExtTCPDSACKRecvSegs 1 0.0
== Receiver
#kernel
IpInReceives 21 0.0
IpInDelivers 21 0.0
TcpPassiveOpens 4 0.0
TcpInSegs 43 0.0
Ip6InReceives 65 0.0
Ip6InDelivers 65 0.0
Ip6InMcastPkts 1 0.0
Ip6InOctets 7658680 0.0
Ip6InMcastOctets 72 0.0
Ip6InNoECTPkts 3889 0.0
Icmp6InNeighborSolicits 1 0.0
Icmp6OutNeighborAdvertisements 1 0.0
Icmp6InType135 1 0.0
Icmp6OutType136 1 0.0
TcpExtTW 3 0.0
TcpExtDelayedACKLost 1 0.0
TcpExtTCPDSACKOldSent 1 0.0
TcpExtTCPRcvCoalesce 197 0.0
TcpExtTCPOFOQueue 30 0.0
IpExtInOctets 2294396 0.0
IpExtInNoECTPkts 1295 0.0
TEST: GREv6/v6 - copy file w/ GSO [FAIL]
2026/01/06 17:25:22 socat[812] W exiting on signal 15
Tests passed: 2
Tests failed: 2
If I increase the timeout to 3 or 4 sec it's enough time to finish the
file transfer regardless of the loss.
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