Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756282AbcKVSLA (ORCPT ); Tue, 22 Nov 2016 13:11:00 -0500 Received: from fmailer.gwdg.de ([134.76.11.16]:47686 "EHLO fmailer.gwdg.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932323AbcKVSK7 (ORCPT ); Tue, 22 Nov 2016 13:10:59 -0500 Date: Tue, 22 Nov 2016 17:59:12 +0100 From: Andre Noll To: Greg KH Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Jiri Slaby , Eric Dumazet , Yibin Yang , Alexander Duyck , Willem de Bruijn , Alexei Starovoitov , "David S. Miller" Subject: Re: Linux 4.4.34 Message-ID: <20161122165912.GA19939@tuebingen.mpg.de> References: <20161121092855.GA20976@kroah.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="MGYHOYXEY6WxJCY8" Content-Disposition: inline In-Reply-To: <20161121092855.GA20976@kroah.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2650 Lines: 91 --MGYHOYXEY6WxJCY8 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Nov 21, 10:28, Greg KH wrote > I'm announcing the release of the 4.4.34 kernel. >=20 > All users of the 4.4 kernel series must upgrade. This update broke PXE boot on our 4-way AMD boxes. The kernel panics in eth_type_trans(), presumably during kernel-level IP autoconfiguration, see [1]. Bisection points me at 5c67f947 (net: __skb_flow_dissect() must cap its return value). And indeed, reverting this commit fixes the problem for me. Investigation showed that the real problem is not the change in the above commit per se (i.e., capping ->thoff) but the fact that in the success case, where we jump to the "out_good" label, ->thoff is now set *after* ->n_proto and ->ip_proto. I fail to see how order matters here, but it clearly does, since the crash is 100% reproducible, and is fixed by the commit below (on top of v4.4.34). Please consider applying something like the patch below for mainline and -stable. Thanks Andre [1] http://people.tuebingen.mpg.de/maan/.eth_type_trans_panic.png --- commit 3494d99764da2b7bbac5d0eed364d03552fefd36 Author: Andre Noll Date: Tue Nov 22 11:34:11 2016 +0100 net: __skb_flow_dissect() must set ->thoff *after* ->n_proto and ->ip_p= roto =20 Without this, PXE boot fails on some AMD Opteron machines. =20 Signed-off-by: Andre Noll diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index 9aba9e9..fde26e4 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -491,18 +491,17 @@ ip_proto_again: =20 out_good: ret =3D true; - - key_control->thoff =3D (u16)nhoff; + goto out; +out_bad: + ret =3D false; out: key_basic->n_proto =3D proto; key_basic->ip_proto =3D ip_proto; - + if (ret) + key_control->thoff =3D (u16)nhoff; + else + key_control->thoff =3D min_t(u16, nhoff, skb ? skb->len : hlen); return ret; - -out_bad: - ret =3D false; - key_control->thoff =3D min_t(u16, nhoff, skb ? skb->len : hlen); - goto out; } EXPORT_SYMBOL(__skb_flow_dissect); --=20 Max Planck Institute for Developmental Biology Spemannstra=C3=9Fe 35, 72076 T=C3=BCbingen, Germany. Phone: (+49) 7071 601 = 829 http://people.tuebingen.mpg.de/maan/ --MGYHOYXEY6WxJCY8 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAlg0eWAACgkQWto1QDEAkw8T+wCfTeWemruQIvG9hSDzphMuTGt6 IoUAniR0EPHG/NRH6OSqMhHJWJxHZx3z =QEbd -----END PGP SIGNATURE----- --MGYHOYXEY6WxJCY8--