[mpich-discuss] MPI-IO of multidimensional arrays - issue reported by valgrind

[Turlough Downes]

Hi All,
	I'm using MPI-IO to let multiple processes write their own subarrays to a single file which will then contain a global array - this is for an astrophysical fluid dynamics simulation code which is parallelised using domain decomposition.  
	To do this I'm using MPI_Type_create_subarray(), MPI_File_open(), MPI_File_set_view() and MPI_File_write_all().  My problem is that my code is occasionally hanging on output on a Blue Gene/P system.  To study this a bit more I tried running the code on my workstation.  When I run this code on my local system using mpich2 (version 1.2.1) on a CentOS 8 core system using valgrind I find that the following error being reported:

==10315== Conditional jump or move depends on uninitialised value(s)
==10315==    at 0x4C86DE8: (within /usr/lib64/mpich2/lib/libmpich.so.1.2)
==10315==    by 0x4C88F0E: ADIOI_GEN_WriteStridedColl (in /usr/lib64/mpich2/lib/libmpich.so.1.2)
==10315==    by 0x4D678C6: MPIOI_File_write_all (in /usr/lib64/mpich2/lib/libmpich.so.1.2)
==10315==    by 0x4D679B8: PMPI_File_write_all (in /usr/lib64/mpich2/lib/libmpich.so.1.2)
==10315==    by 0x41B6B4: hydra_write_single_binary_file (out_binary_single_file.c:101)

where the line number 101 in my code is the line which calls MPI_File_write_all().  My question is this: is this issue being reported by valgrind something to worry about?  It is happening somewhere inside the MPICH2 library itself so this isn't something I myself have delved into too much.  
	I know that any error like this may not have an analogue in the version of MPI used on Blue Gene/P systems, but I thought it might be worth chasing down a little.

	Thanks for any  help.

	Turlough

-- 
Dr Turlough Downes 
Senior Lecturer,
School of Mathematical Sciences,
Dublin City University,
Glasnevin,
Dublin 9,
Ireland.

Tel: +353 1 700 5270 (DCU) 
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