[mpich2-dev] Bug in ch3 MPIDI_Accumulate()?

[David Gingold]

I ran into this problem in code that I cribbed from the ch3  
implementation.  I've not verified that it happens in ch3, but it  
seems, by inspection, that it probably does:

In MPIDI_Accumulate() (ch3u_rma_ops.c), in the case where target_rank  
== rank and the origin and target datatypes are not both pre-defined,  
the code does this:

	    MPID_Datatype_get_ptr(target_datatype, dtp);
	    vec_len = dtp->n_contig_blocks * target_count + 1;

The trouble is that we'll hit this case where the origin type is  
derived and the target type is pre-defined.  And MPID_Datatype_get_ptr 
() isn't workable for pre-defined datatypes.  So dtp->* will evaluate  
to zero.  That causes grief when we reference dtp->eltype a few lines  
down.

I think the simple fix is to add separate cases in here for when  
target_datatype is predefined.  But I also spotted the code in  
MPIR_Datatype_builtin_fillin(), which, if called, would seem to make  
MPID_Datatype_get_ptr() become valid for built-in datatypes.  Is  
there a reason why MPIR_Datatype_builtin_fillin() isn't simply called  
inside MPI_Init() somwehere?

-dg

--
David Gingold
Principal Software Engineer
SiCortex
Three Clock Tower Place, Suite 210
Maynard MA 01754
(978) 897-0214 x224



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