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Scot Breitenfeld
d8ec63966c
The Fortran example set sel_type = H5S_BLOCK_F on the branch where a rank
calls H5Sselect_none (no data to contribute) and H5S_ALL_F on the branch
where a rank sets a real hyperslab, which is backwards. The equivalent C
example (ph5_filtered_writes_no_sel.c) does the opposite:
H5Dwrite(..., no_selection ? H5S_ALL : H5S_BLOCK, ...);
i.e. H5S_ALL when there is no selection (mirrors the file dataspace's own
empty selection) and H5S_BLOCK when a hyperslab was set (memory buffer
matches the block shape of the file selection).
With the inversion, H5Dwrite_f feeds a bogus selection into the collective
filtered I/O path, corrupting the element/byte-length accounting in
H5D__mpio_collective_filtered_chunk_update, which segfaults inside
H5D_select_io_mem -> H5VM_memcpyvv on 12 MPI ranks. Reproduces on current
develop; the bug has been present since the example was added in #3916.