Bug#9459 - deadlock with flush with lock, and lock table write

Added a check before taking a global read lock if
the own thread has a write locked table.

mysql-test/r/flush.result

@@ -27,3 +27,24 @@ select * from t1;
 n
 345
 drop table t1;
+create table t1 (c1 int);
+lock table t1 write;
+flush tables with read lock;
+ERROR HY000: Can't execute the given command because you have active locked tables or an active transaction
+lock table t1 read;
+flush tables with read lock;
+lock table t1 write;
+ERROR HY000: Can't execute the query because you have a conflicting read lock
+lock table t1 read;
+lock table t1 write;
+ERROR HY000: Can't execute the query because you have a conflicting read lock
+unlock tables;
+create table t2 (c1 int);
+create table t3 (c1 int);
+lock table t1 read, t2 read, t3 write;
+flush tables with read lock;
+ERROR HY000: Can't execute the given command because you have active locked tables or an active transaction
+lock table t1 read, t2 read, t3 read;
+flush tables with read lock;
+unlock tables;
+drop table t1, t2, t3;

mysql-test/t/flush.test

@@ -70,4 +70,35 @@ insert into t1 values (345);
 select * from t1;
 drop table t1;
 
+#
+# Bug#9459 - deadlock with flush with lock, and lock table write
+#
+create table t1 (c1 int);
+lock table t1 write;
+# Cannot get the global read lock with write locked tables.
+--error 1192
+flush tables with read lock;
+lock table t1 read;
+# Can get the global read lock with read locked tables.
+flush tables with read lock;
+--error 1223
+lock table t1 write;
+lock table t1 read;
+--error 1223
+lock table t1 write;
+# Release all table locks and the global read lock.
+unlock tables;
+create table t2 (c1 int);
+create table t3 (c1 int);
+lock table t1 read, t2 read, t3 write;
+# Cannot get the global read lock with write locked tables.
+--error 1192
+flush tables with read lock;
+lock table t1 read, t2 read, t3 read;
+# Can get the global read lock with read locked tables.
+flush tables with read lock;
+# Release all table locks and the global read lock.
+unlock tables;
+drop table t1, t2, t3;
+
 # End of 4.1 tests

sql/sql_parse.cc

@@ -5027,6 +5027,23 @@ bool reload_acl_and_cache(THD *thd, ulong options, TABLE_LIST *tables,
   {
     if ((options & REFRESH_READ_LOCK) && thd)
     {
+      /*
+        We must not try to aspire a global read lock if we have a write
+        locked table. This would lead to a deadlock when trying to
+        reopen (and re-lock) the table after the flush.
+      */
+      if (thd->locked_tables)
+      {
+        THR_LOCK_DATA **lock_p= thd->locked_tables->locks;
+        THR_LOCK_DATA **end_p= lock_p + thd->locked_tables->lock_count;
+
+        for (; lock_p < end_p; lock_p++)
+          if ((*lock_p)->type == TL_WRITE)
+          {
+            my_error(ER_LOCK_OR_ACTIVE_TRANSACTION, MYF(0));
+            return 1;
+          }
+      }
       /*
 	Writing to the binlog could cause deadlocks, as we don't log
 	UNLOCK TABLES