Jeff, Thank you for the help. Indeed, changing the disp_unit on MPI_Win_allocate from MPI_INT to sizeof(MPI_INT) does eliminate the seg faults in the subsequent window accesses. Rajeev, I am not getting any compiler warnings for using int or literals for target_disp on my machine, but I did change all instances to MPI_Aint just in case. Possibly running this code with some other compiler would show warnings. I am using mpic++/g++ on Ubuntu. I vaguely remember from the MPI-3.0 documentation (but can't seem to find it now) that the disp_unit on window creation and on any subsequent atomic operations had to match. I get the impression that the datatype passed to Get/Put does not determine the length in bytes of the stride used with target_disp. Instead the disp_unit at window creation is used. In this case it would seem to me that asking to Put/Get data with a target_disp of 1 and an original disp_unit of 1275069445 would definitely seg fault since the buffer and window are only a few tens of bytes long. But as I said earlier, I am by no means an expert. Still learning my way around. Thanks again to both of you for the help. I am not sure I would've ever caught that myself! Corey On Sat, Jan 18, 2014 at 4:56 PM, Jeff Hammond <[email protected]>wrote:

Hi Corey,

It was a simple bug. You passed MPI_INT as the disp_unit rather than sizeof(int), which is almost certainly what you meant. MPI_INT is an opaque handle that is 1275069445 when interpreted as an integer.

I am not entirely sure why using such a large disp_unit caused the segfault though. I haven't yet figured out where disp_unit is used in the MPI_Get code.

Best,

Jeff

On Sat, Jan 18, 2014 at 2:41 PM, Corey A. Henderson <[email protected]> wrote:

...

I am having a problem where I cannot set the target_disp parameter to a positive value in any of the 1-sided calls I've tried (EG: MPI_Put, MPI_Get, MPI_Fetch_and_op, etc.)

I am trying to use a shared (lock_all) approach with flushes. When I set target_disp to zero, the messaging works fine as expected. If I use a positive value I always get a Seg fault.

Obligatory disclaimer: I am not a c or MPI expert so it's entirely possible I've made some newbie error here. But I am at my wit's end trying to figure this out and could use help.

Info: MPICH 3.0.4 built on Ubuntu 12.04 LTS running one node on Intel® Core™ i5-3570K CPU @ 3.40GHz × 4

I've attached the code I've isolated to show the problem. With the targetDisp int set to 0, the data is properly transferred. If it is set to 1, or sizeof(int), I get the following seg fault from mpiexec for targetDisp>0.

corey@UbuntuDesktop:~/workspace/TargetDispBug/Release$ mpiexec -n 2 ./TargetDispBug

===================================================================================

...

= BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES = EXIT CODE: 139 = CLEANING UP REMAINING PROCESSES = YOU CAN IGNORE THE BELOW CLEANUP MESSAGES

===================================================================================

...

YOUR APPLICATION TERMINATED WITH THE EXIT STRING: Segmentation fault (signal 11) This typically refers to a problem with your application. Please see the FAQ page for debugging suggestions

However, for targetDisp == 0 I get (as expected):

corey@UbuntuDesktop:~/workspace/TargetDispBug/Release$ mpiexec -n 2 ./TargetDispBug Received: 42.

The seg fault occurs at the MPI_Win_flush on both processes for targetDisp>0 on either the Put or Get or both.

Any help with this would be great.

Code follows:

#include "mpi.h"

int main(int argc, char* argv[]){

// Test main for one sided message queueing int rank, numranks, targetDisp = 0; int sizeInBytes = 10*sizeof(int), *buffer; MPI_Win window;

MPI_Init(&argc, &argv);

MPI_Comm_rank(MPI_COMM_WORLD, &rank); MPI_Comm_size(MPI_COMM_WORLD, &numranks);

MPI_Win_allocate(sizeInBytes, MPI_INT, MPI_INFO_NULL, MPI_COMM_WORLD, &buffer, &window);

MPI_Win_lock_all(0, window);

int *sendBuffer; int *receiveBuffer;

MPI_Alloc_mem(sizeof(int), MPI_INFO_NULL, &sendBuffer); MPI_Alloc_mem(sizeof(int), MPI_INFO_NULL, &receiveBuffer);

if (rank == 1) {

sendBuffer[0] = 42;

MPI_Put(sendBuffer, 1, MPI_INT, 0, targetDisp, 1, MPI_INT, window);

MPI_Win_flush(0, window);

}

MPI_Barrier(MPI_COMM_WORLD);

if (rank == 0) {

MPI_Get(receiveBuffer, 1, MPI_INT, 0, targetDisp, 1, MPI_INT, window);

MPI_Win_flush(0, window);

printf("Received: %d.\n", receiveBuffer[0]);

}

MPI_Win_unlock_all(window);

MPI_Free_mem(sendBuffer); MPI_Free_mem(receiveBuffer);

MPI_Win_free(&window);

MPI_Finalize(); return 0;

}

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-- Jeff Hammond [email protected]