Re: [PATCH] IB/mlx4: Fix CM REQ retries in paravirt mode

[jackm <jackm-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>]

Nice catch, Haakon!

-Jack

On Tue, 20 Jun 2017 14:07:50 +0200
Håkon Bugge <Haakon.Bugge-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> wrote:

> CM REQs cannot be successfully retried, because a new pv_cm_id is
> created for each request, without checking if one already exists.
> 
> By checking if an id exists before creating one, the bug is fixed.
> 
> This bug can be provoked by running an RDMA CM user-land application,
> but inserting a five seconds delay before the rdma_accept() call on
> the passive side. This delay is larger than the default CMA timeout,
> and triggers a retry from the active side. The retried REQ will use
> another pv_cm_id (the cm_id on the wire). This confuses the CM
> protocol and two REJs are sent from the passive side.
> 
> Here is an excerpt from ibdump running without the patch:
> 
> 3.285092       LID: 4 -> LID: 4       SDP 290 CM: ConnectRequest(SDP
> Hello) 7.382711       LID: 4 -> LID: 4       SDP 290 CM:
> ConnectRequest(SDP Hello) 7.382861       LID: 4 -> LID: 4
> InfiniBand 290 CM: ConnectReject 7.387644       LID: 4 -> LID:
> 4       InfiniBand 290 CM: ConnectReject
> 
> and here is the same with bug fix applied:
> 
> 3.251010       LID: 4 -> LID: 4       SDP 290 CM: ConnectRequest(SDP
> Hello) 7.349387       LID: 4 -> LID: 4       SDP 290 CM:
> ConnectRequest(SDP Hello) 8.258443       LID: 4 -> LID: 4       SDP
> 290 CM: ConnectReply(SDP Hello) 8.259890       LID: 4 -> LID: 4
> InfiniBand 290 CM: ReadyToUse
> 
> Suggested-by: Venkat Venkatsubra <venkat.x.venkatsubra-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Håkon Bugge <haakon.bugge-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> Reported-by: Wei Lin Guay <wei.lin.guay-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> Tested-by: Wei Lin Guay <wei.lin.guay-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> Reviewed-by: Yuval Shaia <yuval.shaia-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>

Acked-by: Jack Morgenstein <jackm-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>
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