From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756825AbeDZQFq (ORCPT ); Thu, 26 Apr 2018 12:05:46 -0400 Received: from aserp2120.oracle.com ([141.146.126.78]:41884 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756519AbeDZQFo (ORCPT ); Thu, 26 Apr 2018 12:05:44 -0400 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 11.3 \(3445.6.18\)) Subject: Re: [PATCH] IB/core: Make ib_mad_client_id atomic From: =?utf-8?Q?H=C3=A5kon_Bugge?= In-Reply-To: <20180423221618.0000795d@dev.mellanox.co.il> Date: Thu, 26 Apr 2018 18:06:10 +0200 Cc: Don Hiatt , Ira Weiny , Sean Hefty , OFED mailing list , linux-kernel@vger.kernel.org, jackm Message-Id: References: <20180418142450.15581-1-Haakon.Bugge@oracle.com> <1524196555.11756.30.camel@redhat.com> <20180420153451.GF30433@ziepe.ca> <50E3FE4A-2C6E-4493-92E1-383C349FAE3A@oracle.com> <20180423221618.0000795d@dev.mellanox.co.il> To: Jason Gunthorpe , Doug Ledford X-Mailer: Apple Mail (2.3445.6.18) X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8875 signatures=668698 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=3 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=848 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1804260151 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id w3QG5rnR010646 > On 23 Apr 2018, at 21:16, jackm wrote: > > On Mon, 23 Apr 2018 16:19:57 +0200 > Håkon Bugge wrote: > > >>> >>> This actually looks like a genuine bug, why is it described only as >>> 'confusing'? ib_register_mad_agent is callable from userspace, so at >>> least two userspace agents can race and get the same TID’s. >> >> My understanding is that every lookup is using the {port, TID} tuple. >> As such, it is not a bug, but, very confusing. > Haakon, you are correct (see snippet from the IB spec, below). > > We will NOT have a situation where there are 2 threads/apps > with the same agent ID on the *same port* (accessing the agent ID > allocator is protected by a per-port spinlock). Having the same agent ID > on DIFFERENT ports is OK. > Thus, there is NO bug here. (But as Haakon says, IMHO it is more robust > to avoid having the same agent ID for 2 agents even if those agents are > on different ports). > >> >>> TIDs need to be globally unique on the entire machine. >> > Jason, that is not exactly correct. > > From the IB Spec 1.3, C13-18.1.1 (in section 13.4.6.4 - TransactionID > usage): > "When initiating a new operation, MADHeader:TransactionID > shall be set to such a value that within that MAD the combination of > TID, SGID, and MgmtClass is different from that of any other currently > executing operation. If the MAD does not have a GRH, its SLID is used > in the combination in place of an SGID." > > Since the SGID/SLID is different for each port, the per-port guarantee > of no 2 agents receiving the same agent-ID value is sufficient. > > -Jack Shall I interpret this silence as my commit is good to go or that I should add Jack’s tangible information to the commit message? Thxs, Håkon