RE: [PATCH 0/3] Fix request completion holes

["Steve Wise" <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>]

> 
> > iWARP spec too.   This is in regard to completion ordering though.  The
local
> > invalidate send WR must have the IB_SEND_FENCE flag set if you want it to
only
> > be executed after all prior send WRs are executed.
> 
> Oh right, yes, you need to have local invalidate fence to guarentee
> that, but usually a local operation will not refer to a RKEY, so
> execution ordering wont matter.
> 
> But this is a good general point, doesn't a ULP need to set FENCE on
> SEND, eg:
> 
>  RDMA READ (rkey)
>  RDMA READ (rkey)
>  SEND w/ FENCE (tell remote to invalidate rkey)
> 
> Otherwise IBA Table 79 says RDMA READ can pass SEND and we have a
> situation where the rkey has become invalidated when the remote is
> still trying to use it.
> 
> IBA actually explicitly calls this out (pg 538):
> 
>  RDMA Read operations may be executed at the target after subse-
>  quent Send and Invalidate operation already performed the invalida-
>  tion at the target. That may cause the RDMA Read operation to fail.
>  Setting the Fence Indicator on the subsequent operations guarantees
>  that the RDMA Read will fully complete before the invalidation takes
>  place.
> 
> None of our ULPs use IB_SEND_FENCE - so this is a bug!
> 

I think the nvmf target doesn't post the SEND_W_INVALIDATE (NVMF CQE) until the
RDMA READ(s) (and back end BIO submission) complete. 

Steve.

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