dm vdo: don't refer to dedupe_context after releasing it

Clear the dedupe_context pointer in a data_vio whenever ownership of
the context is lost, so that vdo can't examine it accidentally.
Signed-off-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

drivers/md/dm-vdo/dedupe.c

@@ -729,6 +729,7 @@ static void process_update_result(struct data_vio *agent)
 	    !change_context_state(context, DEDUPE_CONTEXT_COMPLETE, DEDUPE_CONTEXT_IDLE))
 		return;
 
+	agent->dedupe_context = NULL;
 	release_context(context);
 }
 
@@ -1648,6 +1649,7 @@ static void process_query_result(struct data_vio *agent)
 
 	if (change_context_state(context, DEDUPE_CONTEXT_COMPLETE, DEDUPE_CONTEXT_IDLE)) {
 		agent->is_duplicate = decode_uds_advice(context);
+		agent->dedupe_context = NULL;
 		release_context(context);
 	}
 }
@@ -2321,6 +2323,7 @@ static void timeout_index_operations_callback(struct vdo_completion *completion)
 		 * send its requestor on its way.
 		 */
 		list_del_init(&context->list_entry);
+		context->requestor->dedupe_context = NULL;
 		continue_data_vio(context->requestor);
 		timed_out++;
 	}