ompi/request: change semantics of ompi request callbacks

This commit changes the sematics of ompi request callbacks. If a
request's callback has freed or re-posted (using start) a request
the callback must return 1 instead of OMPI_SUCCESS. This indicates
to ompi_request_complete that the request should not be modified
further. This fixes a race condition in osc/pt2pt that could lead
to the req_state being inconsistent if a request is freed between
the callback and setting the request as complete.

Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>

ompi/mca/osc/pt2pt/osc_pt2pt.h

@@ -265,9 +265,6 @@ struct ompi_osc_pt2pt_module_t {
     /** Lock for garbage collection lists */
     opal_mutex_t gc_lock;
 
-    /** List of requests that need to be freed */
-    opal_list_t request_gc;
-
     /** List of buffers that need to be freed */
     opal_list_t buffer_gc;
 };
@@ -658,41 +655,26 @@ static inline void osc_pt2pt_copy_for_send (void *target, size_t target_len, con
 }
 
 /**
- * osc_pt2pt_request_gc_clean:
+ * osc_pt2pt_gc_clean:
  *
  * @short Release finished PML requests and accumulate buffers.
  *
- * @long This function exists because it is not possible to free a PML request
- *       or buffer from a request completion callback. We instead put requests
- *       and buffers on the module's garbage collection lists and release then
- *       at a later time.
+ * @long This function exists because it is not possible to free a buffer from
+ *     a request completion callback. We instead put requests and buffers on the
+ *     module's garbage collection lists and release then at a later time.
  */
 static inline void osc_pt2pt_gc_clean (ompi_osc_pt2pt_module_t *module)
 {
     ompi_request_t *request;
     opal_list_item_t *item;
 
     OPAL_THREAD_LOCK(&module->gc_lock);
-
-    while (NULL != (request = (ompi_request_t *) opal_list_remove_first (&module->request_gc))) {
-        OPAL_THREAD_UNLOCK(&module->gc_lock);
-        ompi_request_free (&request);
-        OPAL_THREAD_LOCK(&module->gc_lock);
-    }
-
     while (NULL != (item = opal_list_remove_first (&module->buffer_gc))) {
         OBJ_RELEASE(item);
     }
-
     OPAL_THREAD_UNLOCK(&module->gc_lock);
 }
 
-static inline void osc_pt2pt_gc_add_request (ompi_osc_pt2pt_module_t *module, ompi_request_t *request)
-{
-    OPAL_THREAD_SCOPED_LOCK(&module->gc_lock,
-                            opal_list_append (&module->request_gc, (opal_list_item_t *) request));
-}
-
 static inline void osc_pt2pt_gc_add_buffer (ompi_osc_pt2pt_module_t *module, opal_list_item_t *buffer)
 {
     OPAL_THREAD_SCOPED_LOCK(&module->gc_lock,

ompi/mca/osc/pt2pt/osc_pt2pt_comm.c

@@ -45,10 +45,9 @@ static int ompi_osc_pt2pt_comm_complete (ompi_request_t *request)
 
     mark_outgoing_completion(module);
 
-    /* put this request on the garbage colletion list */
-    osc_pt2pt_gc_add_request (module, request);
+    ompi_request_free (&request);
 
-    return OMPI_SUCCESS;
+    return 1;
 }
 
 static int ompi_osc_pt2pt_req_comm_complete (ompi_request_t *request)
@@ -101,10 +100,9 @@ static int ompi_osc_pt2pt_dt_send_complete (ompi_request_t *request)
     OPAL_THREAD_UNLOCK(&mca_osc_pt2pt_component.lock);
     assert (NULL != module);
 
-    /* put this request on the garbage colletion list */
-    osc_pt2pt_gc_add_request (module, request);
+    ompi_request_free (&request);
 
-    return OMPI_SUCCESS;
+    return 1;
 }
 
 /* self communication optimizations */

ompi/mca/osc/pt2pt/osc_pt2pt_component.c

@@ -320,7 +320,6 @@ component_select(struct ompi_win_t *win, void **base, size_t size, int disp_unit
     OBJ_CONSTRUCT(&module->locks_pending_lock, opal_mutex_t);
     OBJ_CONSTRUCT(&module->outstanding_locks, opal_hash_table_t);
     OBJ_CONSTRUCT(&module->pending_acc, opal_list_t);
-    OBJ_CONSTRUCT(&module->request_gc, opal_list_t);
     OBJ_CONSTRUCT(&module->buffer_gc, opal_list_t);
     OBJ_CONSTRUCT(&module->gc_lock, opal_mutex_t);
     OBJ_CONSTRUCT(&module->all_sync, ompi_osc_pt2pt_sync_t);

ompi/mca/osc/pt2pt/osc_pt2pt_data_move.c

@@ -238,10 +238,8 @@ static int ompi_osc_pt2pt_control_send_unbuffered_cb (ompi_request_t *request)
     /* free the temporary buffer */
     free (ctx);
 
-    /* put this request on the garbage colletion list */
-    osc_pt2pt_gc_add_request (module, request);
-
-    return OMPI_SUCCESS;
+    ompi_request_free (&request);
+    return 1;
 }
 
 /**
@@ -437,10 +435,8 @@ static int osc_pt2pt_incoming_req_complete (ompi_request_t *request)
 
     mark_incoming_completion (module, rank);
 
-    /* put this request on the garbage colletion list */
-    osc_pt2pt_gc_add_request (module, request);
-
-    return OMPI_SUCCESS;
+    ompi_request_free (&request);
+    return 1;
 }
 
 struct osc_pt2pt_get_post_send_cb_data_t {
@@ -460,10 +456,8 @@ static int osc_pt2pt_get_post_send_cb (ompi_request_t *request)
     /* mark this as a completed "incoming" request */
     mark_incoming_completion (module, rank);
 
-    /* put this request on the garbage colletion list */
-    osc_pt2pt_gc_add_request (module, request);
-
-    return OMPI_SUCCESS;
+    ompi_request_free (&request);
+    return 1;
 }
 
 /**
@@ -699,9 +693,7 @@ static int accumulate_cb (ompi_request_t *request)
         osc_pt2pt_gc_add_buffer (module, &acc_data->super);
     }
 
-    /* put this request on the garbage colletion list */
-    osc_pt2pt_gc_add_request (module, request);
-
+    ompi_request_free (&request);
     return ret;
 }
 
@@ -771,13 +763,11 @@ static int replace_cb (ompi_request_t *request)
 
     mark_incoming_completion (module, rank);
 
-    /* put this request on the garbage colletion list */
-    osc_pt2pt_gc_add_request (module, request);
-
     /* unlock the accumulate lock */
     ompi_osc_pt2pt_accumulate_unlock (module);
 
-    return OMPI_SUCCESS;
+    ompi_request_free (&request);
+    return 1;
 }
 
 /**
@@ -1435,13 +1425,11 @@ static int process_large_datatype_request_cb (ompi_request_t *request)
         return OMPI_ERROR;
     }
 
-    /* put this request on the garbage colletion list */
-    osc_pt2pt_gc_add_request (module, request);
-
     /* free the datatype buffer */
     osc_pt2pt_gc_add_buffer (module, &ddt_buffer->super);
 
-    return OMPI_SUCCESS;
+    ompi_request_free (&request);
+    return 1;
 }
 
 /**

ompi/mca/osc/pt2pt/osc_pt2pt_frag.c

@@ -37,11 +37,9 @@ static int frag_send_cb (ompi_request_t *request)
     mark_outgoing_completion(module);
     opal_free_list_return (&mca_osc_pt2pt_component.frags, &frag->super);
 
+    ompi_request_free (&request);
 
-    /* put this request on the garbage colletion list */
-    osc_pt2pt_gc_add_request (module, request);
-
-    return OMPI_SUCCESS;
+    return 1;
 }
 
 static int frag_send (ompi_osc_pt2pt_module_t *module, ompi_osc_pt2pt_frag_t *frag)

ompi/mca/osc/pt2pt/osc_pt2pt_module.c

@@ -79,7 +79,6 @@ int ompi_osc_pt2pt_free(ompi_win_t *win)
     OPAL_LIST_DESTRUCT(&module->pending_acc);
 
     osc_pt2pt_gc_clean (module);
-    OPAL_LIST_DESTRUCT(&module->request_gc);
     OPAL_LIST_DESTRUCT(&module->buffer_gc);
     OBJ_DESTRUCT(&module->gc_lock);
 

ompi/request/request.h

@@ -67,8 +67,10 @@ typedef int (*ompi_request_cancel_fn_t)(struct ompi_request_t* request, int flag
 
 /*
  * Optional function called when the request is completed from the MPI
- * library perspective. This function is not allowed to release any
- * ressources related to the request.
+ * library perspective. This function is allowed to release the request if
+ * the request will not be used with ompi_request_wait* or ompi_request_test.
+ * If the function reposts (using start) a request or calls ompi_request_free()
+ * on the request it *MUST* return 1. It should return 0 otherwise.
  */
 typedef int (*ompi_request_complete_fn_t)(struct ompi_request_t* request);
 
@@ -412,24 +414,28 @@ static inline void ompi_request_wait_completion(ompi_request_t *req)
  */
 static inline int ompi_request_complete(ompi_request_t* request, bool with_signal)
 {
+    int rc = 0;
+
     if( NULL != request->req_complete_cb) {
-        request->req_complete_cb( request );
+        rc = request->req_complete_cb( request );
         request->req_complete_cb = NULL;
     }
 
-    if( OPAL_LIKELY(with_signal) ) {
-        if(!OPAL_ATOMIC_CMPSET_PTR(&request->req_complete, REQUEST_PENDING, REQUEST_COMPLETED)) {
-            ompi_wait_sync_t *tmp_sync = (ompi_wait_sync_t *) OPAL_ATOMIC_SWAP_PTR(&request->req_complete,
-                                                                                   REQUEST_COMPLETED);
-            /* In the case where another thread concurrently changed the request to REQUEST_PENDING */
-            if( REQUEST_PENDING != tmp_sync )
-                wait_sync_update(tmp_sync, 1, request->req_status.MPI_ERROR);
+    if (0 == rc) {
+        if( OPAL_LIKELY(with_signal) ) {
+            if(!OPAL_ATOMIC_CMPSET_PTR(&request->req_complete, REQUEST_PENDING, REQUEST_COMPLETED)) {
+                ompi_wait_sync_t *tmp_sync = (ompi_wait_sync_t *) OPAL_ATOMIC_SWAP_PTR(&request->req_complete,
+                                                                                       REQUEST_COMPLETED);
+                /* In the case where another thread concurrently changed the request to REQUEST_PENDING */
+                if( REQUEST_PENDING != tmp_sync )
+                    wait_sync_update(tmp_sync, 1, request->req_status.MPI_ERROR);
+            }
+        } else
+            request->req_complete = REQUEST_COMPLETED;
+
+        if( OPAL_UNLIKELY(MPI_SUCCESS != request->req_status.MPI_ERROR) ) {
+            ompi_request_failed++;
         }
-    } else
-        request->req_complete = REQUEST_COMPLETED;
-
-    if( OPAL_UNLIKELY(MPI_SUCCESS != request->req_status.MPI_ERROR) ) {
-        ompi_request_failed++;
     }
 
     return OMPI_SUCCESS;