osc/rdma: Fix segfault in shared memory peer initialization

Commit 815fe8e changed ompi_osc_rdma_peer_local_base() calls to
ompi_osc_rdma_peer_cpu_atomics() in accumulate operations. This caused
local peers without CPU atomics to fall back to network operations,
but their base_handle was not initialized, leading to a NULL pointer
dereference in the BTL layer.

Fix by setting base_handle for local peers when use_memory_registration
is enabled (indicating BTL requires registered memory handles for RDMA
operations) and use_cpu_atomics is false (forcing network fallback).

Signed-off-by: Shi Jin <[email protected]>

Author: shijin-aws

ompi/mca/osc/rdma/osc_rdma_component.c

@@ -18,7 +18,7 @@
  * Copyright (c) 2015-2017 Intel, Inc. All rights reserved.
  * Copyright (c) 2016-2017 IBM Corporation. All rights reserved.
  * Copyright (c) 2018      Cisco Systems, Inc.  All rights reserved
- * Copyright (c) 2018-2022 Amazon.com, Inc. or its affiliates.
+ * Copyright (c) 2018-2025 Amazon.com, Inc. or its affiliates.
  *                         All Rights reserved.
  * Copyright (c) 2019      Research Organization for Information Science
  *                         and Technology (RIST).  All rights reserved.
@@ -867,6 +867,16 @@ static int allocate_state_shared (ompi_osc_rdma_module_t *module, void **base, s
                 if (use_cpu_atomics) {
                     peer->flags |= OMPI_OSC_RDMA_PEER_CPU_ATOMICS;
                 }
+
+                /* set base_handle for local peers when memory registration is used */
+                if (module->use_memory_registration && !use_cpu_atomics) {
+                    if (MPI_WIN_FLAVOR_ALLOCATE == module->flavor) {
+                        ex_peer->super.base_handle = module->state_handle;
+                    } else {
+                        ex_peer->super.base_handle = module->base_handle;
+                    }
+                }
+
                 offset += temp[i].size;
                 offset += OPAL_ALIGN_PAD_AMOUNT(offset, memory_alignment);
             } else {