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From: "Håkon Bugge" <haakon.bugge@oracle.com>
To: Jason Gunthorpe <jgg@ziepe.ca>, Doug Ledford <dledford@redhat.com>
Cc: Don Hiatt <don.hiatt@intel.com>, Ira Weiny <ira.weiny@intel.com>,
	Sean Hefty <sean.hefty@intel.com>,
	OFED mailing list <linux-rdma@vger.kernel.org>,
	linux-kernel@vger.kernel.org, jackm <jackm@dev.mellanox.co.il>
Subject: Re: [PATCH] IB/core: Make ib_mad_client_id atomic
Date: Thu, 26 Apr 2018 18:06:10 +0200	[thread overview]
Message-ID: <C546E163-297B-438E-AF76-CC04247ABFBA@oracle.com> (raw)
In-Reply-To: <20180423221618.0000795d@dev.mellanox.co.il>



> On 23 Apr 2018, at 21:16, jackm <jackm@dev.mellanox.co.il> wrote:
> 
> On Mon, 23 Apr 2018 16:19:57 +0200
> Håkon Bugge <haakon.bugge@oracle.com> 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

  reply	other threads:[~2018-04-26 16:05 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-18 14:24 Håkon Bugge
2018-04-18 18:51 ` Weiny, Ira
2018-04-19  2:59 ` Yanjun Zhu
2018-04-20  3:55 ` Doug Ledford
2018-04-20 15:34   ` Jason Gunthorpe
2018-04-23 14:19     ` Håkon Bugge
2018-04-23 19:16       ` jackm
2018-04-26 16:06         ` Håkon Bugge [this message]
2018-04-26 18:32           ` jackm
     [not found]             ` <9fdd3ec4-ee91-5442-e753-25d2ecd27ea9@xsintricity.com>
     [not found]               ` <A58D5192-06E7-46A3-869C-273E9A2BC128@oracle.com>
2018-04-27 19:08                 ` Doug Ledford
2018-04-30 11:50                   ` Håkon Bugge
2018-04-30 14:49         ` Jason Gunthorpe
2018-04-30 17:10           ` Doug Ledford
2018-04-30 17:49             ` Weiny, Ira
2018-04-30 23:01             ` Jason Gunthorpe
2018-05-01  4:38             ` jackm
2018-05-01  6:40               ` Håkon Bugge

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