greybus: first operation error prevails

If an operation already has an error result recorded, don't
overwrite it with a new error code.

In order to ensure a request completes exactly once, return a
Boolean indicating whether setting the result was successful.  If
two threads are racing to complete an operation (for example if a
slow-but-normal response message arrives at the same time timeout
processing commences) only the one that sets the final result
will finish its activity.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

diff --git a/drivers/staging/greybus/operation.c b/drivers/staging/greybus/operation.c
index f42e6d2..49b0f19 100644 (file)
--- a/drivers/staging/greybus/operation.c
+++ b/drivers/staging/greybus/operation.c
@@ -66,9 +66,12 @@ struct gb_operation_msg_hdr {
 /* XXX Could be per-host device, per-module, or even per-connection */
 static DEFINE_SPINLOCK(gb_operations_lock);
 
-static void gb_operation_result_set(struct gb_operation *operation, int result)
+static bool gb_operation_result_set(struct gb_operation *operation, int result)
 {
+       if (operation->errno)
+               return false;
        operation->errno = result;
+       return true;
 }
 
 int gb_operation_result(struct gb_operation *operation)
@@ -174,7 +177,7 @@ static void gb_operation_request_handle(struct gb_operation *operation)
 
        gb_connection_err(operation->connection,
                "unexpected incoming request type 0x%02hhx\n", header->type);
-       gb_operation_result_set(operation, -EPROTONOSUPPORT);
+       (void)gb_operation_result_set(operation, -EPROTONOSUPPORT);
 }
 #endif
 
@@ -512,8 +515,8 @@ greybus_data_sent(struct greybus_host_device *hd, void *header, int status)
        /* XXX Right now we assume we're an outgoing request */
        message = gb_hd_message_find(hd, header);
        operation = message->operation;
-       gb_operation_result_set(operation, status);
-       queue_work(gb_operation_workqueue, &operation->work);
+       if (gb_operation_result_set(operation, status))
+               queue_work(gb_operation_workqueue, &operation->work);
 }
 EXPORT_SYMBOL_GPL(greybus_data_sent);
 
@@ -538,8 +541,8 @@ void gb_connection_recv_request(struct gb_connection *connection,
        memcpy(operation->request->header, data, size);
 
        /* XXX Right now this will just complete the operation */
-       gb_operation_result_set(operation, -ENOSYS);
-       queue_work(gb_operation_workqueue, &operation->work);
+       if (gb_operation_result_set(operation, -ENOSYS))
+               queue_work(gb_operation_workqueue, &operation->work);
 }
 
 /*
@@ -582,8 +585,8 @@ static void gb_connection_recv_response(struct gb_connection *connection,
                memcpy(message->header, data, size);
 
        /* The rest will be handled in work queue context */
-       gb_operation_result_set(operation, result);
-       queue_work(gb_operation_workqueue, &operation->work);
+       if (gb_operation_result_set(operation, result))
+               queue_work(gb_operation_workqueue, &operation->work);
 }
 
 /*
@@ -630,9 +633,10 @@ void gb_connection_recv(struct gb_connection *connection,
  */
 void gb_operation_cancel(struct gb_operation *operation, int errno)
 {
-       gb_operation_result_set(operation, errno);
-       gb_message_cancel(operation->request);
-       gb_message_cancel(operation->response);
+       if (gb_operation_result_set(operation, errno)) {
+               gb_message_cancel(operation->request);
+               gb_message_cancel(operation->response);
+       }
 }
 
 /**