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

- Make sure the epoch type is set before returning from MPI_Win_start().
- Make sure the group is only free'd if it is valid in MPI_Win_complete().
  - Fix possible double free() of the group.

Signed-off-by: Austen Lauria <awlauria@us.ibm.com>

ompi/mca/osc/rdma/osc_rdma_active_target.c

@@ -385,6 +385,8 @@ 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 */
         OPAL_THREAD_UNLOCK(&module->lock);
@@ -393,8 +395,6 @@ int ompi_osc_rdma_start_atomic (ompi_group_t *group, int mpi_assert, ompi_win_t
 
     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 +466,19 @@ 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);
+        if(MPI_GROUP_EMPTY != group) {
+            OBJ_RELEASE(group);
+        }
+	OPAL_THREAD_UNLOCK(&(module->lock));
         return OMPI_SUCCESS;
     }
 
+    /* phase 2 cleanup group */
+    OBJ_RELEASE(group);
+
     sync->peer_list.peers = NULL;
 
     OPAL_THREAD_UNLOCK(&(module->lock));
@@ -508,7 +510,6 @@ int ompi_osc_rdma_wait_atomic (ompi_win_t *win)
 {
     ompi_osc_rdma_module_t *module = GET_MODULE(win);
     ompi_osc_rdma_state_t *state = module->state;
-    ompi_group_t *group;
     int group_size;
 
     OSC_RDMA_VERBOSE(MCA_BASE_VERBOSE_TRACE, "wait: %s", win->w_name);
@@ -532,12 +533,12 @@ int ompi_osc_rdma_wait_atomic (ompi_win_t *win)
     }
 
     OPAL_THREAD_LOCK(&module->lock);
-    group = module->pw_group;
+    if(MPI_GROUP_EMPTY != module->pw_group) {
+        OBJ_RELEASE(module->pw_group);
+    }
     module->pw_group = NULL;
     OPAL_THREAD_UNLOCK(&module->lock);
 
-    OBJ_RELEASE(group);
-
     OSC_RDMA_VERBOSE(MCA_BASE_VERBOSE_TRACE, "wait complete");
 
     return OMPI_SUCCESS;