From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] ibmveth: set correct gso_size and gso_type Date: Fri, 09 Dec 2016 22:48:15 -0500 (EST) Message-ID: <20161209.224815.1152441346998572864.davem@davemloft.net> References: <1477440555-21133-1-git-send-email-jmaxwell37@gmail.com> <1481236803-4807-1-git-send-email-tlfalcon@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: tlfalcon@linux.vnet.ibm.com Return-path: Received: from shards.monkeyblade.net ([184.105.139.130]:39884 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752090AbcLJDsT (ORCPT ); Fri, 9 Dec 2016 22:48:19 -0500 In-Reply-To: <1481236803-4807-1-git-send-email-tlfalcon@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Thomas Falcon Date: Thu, 8 Dec 2016 16:40:03 -0600 > This patch is based on an earlier one submitted > by Jon Maxwell with the following commit message: > > "We recently encountered a bug where a few customers using ibmveth on the > same LPAR hit an issue where a TCP session hung when large receive was > enabled. Closer analysis revealed that the session was stuck because the > one side was advertising a zero window repeatedly. > > We narrowed this down to the fact the ibmveth driver did not set gso_size > which is translated by TCP into the MSS later up the stack. The MSS is > used to calculate the TCP window size and as that was abnormally large, > it was calculating a zero window, even although the sockets receive buffer > was completely empty." > > We rely on the Virtual I/O Server partition in a pseries > environment to provide the MSS through the TCP header checksum > field. The stipulation is that users should not disable checksum > offloading if rx packet aggregation is enabled through VIOS. > > Some firmware offerings provide the MSS in the RX buffer. > This is signalled by a bit in the RX queue descriptor. > > Reviewed-by: Brian King > Reviewed-by: Pradeep Satyanarayana > Reviewed-by: Marcelo Ricardo Leitner > Reviewed-by: Jonathan Maxwell > Reviewed-by: David Dai > Signed-off-by: Thomas Falcon Applied, although mis-using the TCP checksum field for this is kind of bogus. I'm surprised there wasn't some other place you could stick this value, which wouldn't modify the packet contents.