[mvapich-discuss] MPI_File_read_at_all external32 bug in MV2-2.1

[Adam T. Moody]

Hello MVAPICH team,
I've hit a bug in MPI_File_read_at_all in MVAPICH2-2.1.  I have an 
application that reads and writes files in external32 format.  It writes 
the file just fine, but it throws the following error when reading the 
file back:

internal ABORT - process 0
srun: error: rzmerl2: task 0: Exited with exit code 1
Assertion failed in file src/mpid/common/datatype/mpid_ext32_segment.c 
at line 277: FALSE
memcpy argument memory ranges overlap, dst_=0x2aaab5c160a8 
src_=0x2aaab5c160a8 len_=176

Above, MPI is trying to do a memcpy where the source and destination 
buffer are the same address.  Looking through the code for MVAPICH2-2.1, 
the problem seems to be at line 132 in src/mpi/romio/mpi-io/read_all.c:

    if (e32_buf != NULL) {
        error_code = MPIU_read_external32_conversion_fn(xbuf, datatype,
                count, e32_buf);
    ADIOI_Free(e32_buf);
    }

I think the fix is to change "xbuf" above to "buf" as it is in read.c below:

    if (e32_buf != NULL) {
        error_code = MPIU_read_external32_conversion_fn(buf, datatype,
                count, e32_buf);
    ADIOI_Free(e32_buf);
    }

When in external32 mode, xbuf == e32_buf, which acts as a temporary 
buffer in which to read the data.  The code is then meant to unpack and 
convert the data from the temporary buffer into the user buffer at buf.

It's probably worth checking the other external32 code paths to look for 
similar bugs.
Thanks,
-Adam