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From: jackm <jackm@dev.mellanox.co.il>
To: "Håkon Bugge" <haakon.bugge@oracle.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>,
	Doug Ledford <dledford@redhat.com>,
	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
Subject: Re: [PATCH] IB/core: Make ib_mad_client_id atomic
Date: Thu, 26 Apr 2018 21:32:50 +0300	[thread overview]
Message-ID: <20180426213250.0000515d@dev.mellanox.co.il> (raw)
In-Reply-To: <C546E163-297B-438E-AF76-CC04247ABFBA@oracle.com>

On Thu, 26 Apr 2018 18:06:10 +0200
Håkon Bugge <haakon.bugge@oracle.com> wrote:

> > 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?
> 
> 
Haakon, I think Jason is on vacation this week. Best to wait for his
response.

-Jack

> Thxs, Håkon
> 

  reply	other threads:[~2018-04-26 18:33 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
2018-04-26 18:32           ` jackm [this message]
     [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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