Index: storage/innobase/log/log0log.cc
===================================================================
--- storage/innobase/log/log0log.cc	(revision 5767)
+++ storage/innobase/log/log0log.cc	(working copy)
@@ -1235,6 +1235,9 @@
 		log_sys->current_flush_lsn = log_sys->lsn;
 		MONITOR_INC(MONITOR_PENDING_LOG_FLUSH);
 		os_event_reset(log_sys->flush_event);
+
+		if (log_sys->buf_free == log_sys->buf_next_to_write)
+			goto flush_op;
 	}
 
 	group = UT_LIST_GET_FIRST(log_sys->log_groups);
@@ -1242,6 +1245,8 @@
 	start_offset = log_sys->buf_next_to_write;
 	end_offset = log_sys->buf_free;
 
+	ut_ad(start_offset != end_offset);
+
 	area_start = ut_calc_align_down(start_offset, OS_FILE_LOG_BLOCK_SIZE);
 	area_end = ut_calc_align(end_offset, OS_FILE_LOG_BLOCK_SIZE);
 
@@ -1252,8 +1257,6 @@
 		log_sys->buf + area_end - OS_FILE_LOG_BLOCK_SIZE,
 		log_sys->next_checkpoint_no);
 
-	group = UT_LIST_GET_FIRST(log_sys->log_groups);
-
 	/* Calculate pad_size if needed. */
 	pad_size = 0;
 	if (write_ahead_size > OS_FILE_LOG_BLOCK_SIZE) {
@@ -1300,6 +1303,8 @@
 
 	log_sys_write_completion();
 
+flush_op:
+	ut_ad(lsn <= log_sys->write_lsn);
 	if (srv_unix_file_flush_method == SRV_UNIX_O_DSYNC) {
 		/* O_DSYNC means the OS did not buffer the log file at all:
 		so we have also flushed to disk what we have written */