Merge pull request open-mpi#8779 from awlauria/8677_fix

osc/rdma: Fix MPI_Win_start()/complete() with MPI_GROUP_EMPTY.

Author: awlauria

ompi/mca/osc/rdma/osc_rdma_active_target.c

@@ -385,16 +385,17 @@ int ompi_osc_rdma_start_atomic (ompi_group_t *group, int mpi_assert, ompi_win_t
 
     OSC_RDMA_VERBOSE(MCA_BASE_VERBOSE_TRACE, "start group size %d", sync->num_peers);
 
+    sync->type = OMPI_OSC_RDMA_SYNC_TYPE_PSCW;
+
     if (0 == ompi_group_size (group)) {
         /* nothing more to do. this is an empty start epoch */
+        sync->peer_list.peers = NULL;
         OPAL_THREAD_UNLOCK(&module->lock);
         return OMPI_SUCCESS;
     }
 
     opal_atomic_wmb ();
 
-    sync->type = OMPI_OSC_RDMA_SYNC_TYPE_PSCW;
-
     /* prevent us from entering a passive-target, fence, or another pscw access epoch until
      * the matching complete is called */
     sync->epoch_active = true;
@@ -466,17 +467,14 @@ int ompi_osc_rdma_complete_atomic (ompi_win_t *win)
     sync->type = OMPI_OSC_RDMA_SYNC_TYPE_NONE;
     sync->epoch_active = false;
 
-    /* phase 2 cleanup group */
-    OBJ_RELEASE(group);
-
     peers = sync->peer_list.peers;
     if (NULL == peers) {
-        /* empty peer list */
         OPAL_THREAD_UNLOCK(&(module->lock));
-        OBJ_RELEASE(group);
         return OMPI_SUCCESS;
     }
 
+    OBJ_RELEASE(group);
+
     sync->peer_list.peers = NULL;
 
     OPAL_THREAD_UNLOCK(&(module->lock));