netdev - Re: [PATCH net-next 1/2] tcp: conditionally call ip_icmp_error() from tcp_v4

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Message-ID: <CANn89i+b-Unz959gZzBgn_7Zk7nyGRVgxP2+smaWeYK4_o0mjw@mail.gmail.com>
Date: Thu, 18 Apr 2024 20:14:50 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: David Ahern <dsahern@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org, 
	Neal Cardwell <ncardwell@...gle.com>, Dragos Tatulea <dtatulea@...dia.com>, eric.dumazet@...il.com, 
	Maciej Żenczykowski <maze@...gle.com>, 
	Willem de Bruijn <willemb@...gle.com>, Shachar Kagan <skagan@...dia.com>
Subject: Re: [PATCH net-next 1/2] tcp: conditionally call ip_icmp_error() from tcp_v4_err()

On Thu, Apr 18, 2024 at 8:09 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 18 Apr 2024 19:47:51 +0200 Eric Dumazet wrote:
> > > You have a kernel patch that makes a test fail, and your solution is
> > > changing userspace? The tests are examples of userspace applications and
> > > how they can use APIs, so if the patch breaks a test it is by definition
> > > breaking userspace which is not allowed.
>
> Tests are often overly sensitive to kernel behavior, while this is
> obviously a red flag it's not an automatic nack. The more tests we
> have the more often we'll catch tiny changes. A lot of tests started
> flaking with 6.9 because of the optimizations in the timer subsystem.
> You know where I'm going with this..
>
> > I think the userspace program relied on a bug added in linux in 2020
> >
> > Jakub, I will stop trying to push the patches, this is a lost battle.
>
> If you have the patches ready - please post them.
> I'm happy to take the blame if they actually regress something in
> the wild :(

The series with the 2 patches has been posted already.

The remaining part is a nettest.c fix, that David is not happy with.

diff --git a/tools/testing/selftests/net/nettest.c
b/tools/testing/selftests/net/nettest.c
index cd8a580974480212b45d86f35293b77f3d033473..23d56797900f19890923028af0b7ba162d9d5794
100644
--- a/tools/testing/selftests/net/nettest.c
+++ b/tools/testing/selftests/net/nettest.c
@@ -1744,6 +1744,8 @@ static int connectsock(void *addr, socklen_t
alen, struct sock_args *args)
        if (args->bind_test_only)
                goto out;

+       set_recv_attr(sd, args->version);
+
        if (connect(sd, addr, alen) < 0) {
                if (errno != EINPROGRESS) {
                        log_err_errno("Failed to connect to remote host");

>
> We're pursuing this because real application suffer real problems
> when routing changes cause transient ICMP errors. Users read the RFC
> and then come shouting at us that Linux is buggy.