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; }