netdev - Potential bio_vec networking/igb size dependency?

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Message-ID: <2757afa0-1b27-8480-0830-9638b2495a85@kernel.dk>
Date:   Mon, 11 Oct 2021 16:09:55 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        Jakub Kicinski <kuba@...nel.org>,
        intel-wired-lan@...ts.osuosl.org
Subject: Potential bio_vec networking/igb size dependency?

Hi,

Been working on a change today that changes struct bio_vec, and it works
fine on the storage side. But when I boot the box with the change, I
can't ssh in. If I attempt to use networking on the box (eg to update
packages), it looks like the data is corrupt. Basic things work - I can
dhcp and get an IP and so on, but ssh in yields:

ssh -v box
[...]
debug1: Local version string SSH-2.0-OpenSSH_8.2p1 Ubuntu-4ubuntu0.3
debug1: Remote protocol version 2.0, remote software version OpenSSH_8.2p1 Ubuntu-4ubuntu0.3
debug1: match: OpenSSH_8.2p1 Ubuntu-4ubuntu0.3 pat OpenSSH* compat 0x04000000
debug1: Authenticating to box as 'axboe'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@...nssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@...nssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
Connection closed by 207.135.234.126 port 22

I've got a vm image that I boot on my laptop, and that seems to
work fine. Hence I'm thinking maybe it's an igb issue? But for the
life of me, I cannot figure out wtf it is. I've looked at the skb_frag_t
uses and nothing pops out at me.

Trivial to reproduce, just add the below patch.

diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index 0e9bdd42dafb..e61967fb4643 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -33,6 +33,7 @@ struct bio_vec {
 	struct page	*bv_page;
 	unsigned int	bv_len;
 	unsigned int	bv_offset;
+	unsigned long	foo;
 };
 
 struct bvec_iter {

-- 
Jens Axboe