Re: [PATCH] ib/cm: Change reject message type when destroying cm_id

["Ted H. Kim" <ted.h.kim-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

On 05/15/15 10:06 AM, Hefty, Sean wrote:
>> Did you intend to add an ISSUE B: section to the commit message?
>
> The issue is listed as the missing comm id.  Though, thinking about it
> again, the issue may have been a missing node GUID.  I can't recall now.
> Maybe Ted does.

Imagine the case of the Linux active side sending REQ with it's CM communication
id. When it gets the REP back, the other side's communication ID
will be received and internal CM state updated. So any REJ from this
point on can send both communication IDs.

Now imagine a slightly different case. The active side sends the REQ,
and the passive side responds with MRA. At this point the CM should
update the state with the second communication ID coming in the
MRA. But it does not do so. This is "ISSUE B". This is will require
a different fix from the patch in question to add the communication ID
updating when getting an MRA.

So as a side effect, a REJ issued at this point by the active side
has only its own communication ID. The problem with only one communication ID
REJs is that they are all generated by remote systems from the one being
sent the REJ and therefore might not be unique. The way that TIMEOUT
REJ addresses this is to have a GUID in the ARI to make it unique.
But other REJ codes don't have this.

-ted

> The IB spec is goofy here in that it only allows a CM REQ, once sent,
> to timeout.  It doesn't define an 'abort' case.  The spec also treats
> the connection is being in a single 'REP wait' state, regardless of
> whether an MRA has been received or not.  This change results in
> the 'I got an MRA but I'm waiting for a REP' to be handled the
> same as 'I'm waiting for a REP', at least for the destruction case.


-- 
Ted H. Kim, PhD
Sun/Oracle America             ted.h.kim-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org
5750 Hannum Drive, #200        +1 310-258-7536
Culver City, CA 90230
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