From MySQL:

Fix bug #17264. For alter table on win32 for succesful operation completion
it is used TL_WRITE(=10) lock instead of TL_WRITE_ALLOW_READ(=6), however in
InnoDB handler TL_WRITE is lifted to TL_WRITE_ALLOW_WRITE, which causes race
condition when several clients do alter table simultaneously.

handler/ha_innodb.cc

@@ -6940,6 +6940,17 @@ ha_innobase::store_lock(
 		&& !thd->tablespace_op
 		&& thd->lex->sql_command != SQLCOM_TRUNCATE
 		&& thd->lex->sql_command != SQLCOM_OPTIMIZE
+
+#ifdef __WIN__
+                /* For alter table on win32 for succesful operation
+                completion it is used TL_WRITE(=10) lock instead of
+                TL_WRITE_ALLOW_READ(=6), however here in innodb handler
+                TL_WRITE is lifted to TL_WRITE_ALLOW_WRITE, which causes
+                race condition when several clients do alter table
+                simultaneously (bug #17264). This fix avoids the problem. */
+                && thd->lex->sql_command != SQLCOM_ALTER_TABLE
+#endif
+
 		&& thd->lex->sql_command != SQLCOM_CREATE_TABLE) {
 
 			lock_type = TL_WRITE_ALLOW_WRITE;