From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751321AbeAWD0E (ORCPT ); Mon, 22 Jan 2018 22:26:04 -0500 Received: from aserp2120.oracle.com ([141.146.126.78]:40828 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751151AbeAWD0C (ORCPT ); Mon, 22 Jan 2018 22:26:02 -0500 Subject: Re: [PATCH] net/mlx4_en: ensure rx_desc updating reaches HW before prod db updating To: Jason Gunthorpe Cc: Eric Dumazet , Tariq Toukan , junxiao.bi@oracle.com, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, Saeed Mahameed References: <1515728542-3060-1-git-send-email-jianchao.w.wang@oracle.com> <339a7156-9ef1-1f3c-30b8-3cc3558d124e@mellanox.com> <1516552998.3478.5.camel@gmail.com> <460fca68-f8a8-e3c4-2e60-e90dc0e2f843@oracle.com> <20180122154734.GD14372@ziepe.ca> From: "jianchao.wang" Message-ID: Date: Tue, 23 Jan 2018 11:25:55 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <20180122154734.GD14372@ziepe.ca> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8782 signatures=668655 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=995 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1801230042 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jason Thanks for your kindly response. On 01/22/2018 11:47 PM, Jason Gunthorpe wrote: >>> Yeah, mlx4 NICs in Google fleet receive trillions of packets per >>> second, and we never noticed an issue. >>> >>> Although we are using a slightly different driver, using order-0 pages >>> and fast pages recycling. >>> >>> >> The driver we use will will set the page reference count to (size of pages)/stride, the >> pages will be freed by networking stack when the reference become zero, and the order-3 >> pages maybe allocated soon, this give NIC device a chance to corrupt the pages which have >> been allocated by others, such as slab. > But it looks like the wmb() is placed when stuffing new rx descriptors > into the device - how can it prevent corruption of pages where > ownership was transfered from device to the host? That sounds more like a > rmb() is missing someplace to me... > The device may see the prod_db updating before rx_desc updating. Then it will get stale rx_descs. These stale rx_descs may contain pages that has been freed to host. > (Granted the missing wmb() is a bug, but it may not be fully solving this > issue??)the wmb() here fix one of the customer's test case. Thanks Jianchao