Bug# 11763784 (former 56541)

ASSERTION TABLE->DB_STAT FAILED IN
SQL_BASE.CC::OPEN_TABLE() DURING I_S Q

This assert could be triggered if a statement requiring a name
lock on a table (e.g. DROP TRIGGER) executed concurrently
with an I_S query which also used the table.

One connection first started an I_S query that opened a given table.
Then another connection started a statement requiring a name lock
on the same table. This statement was blocked since the table was
in use by the I_S query. When the I_S query resumed and tried to
open the table again as part of get_all_tables(), it would encounter
a table instance with an old version number representing the pending
name lock. Since I_S queries ignore version checks and thus pending
name locks, it would try to continue. This caused it to encounter
the assert. The assert checked that the TABLE instance found with a
different version, was a real, open table. However, since this TABLE
instance instead represented a pending name lock, the check would
fail and trigger the assert.

This patch fixes the problem by removing the assert. It is ok for
TABLE::db_stat to be 0 in this case since the TABLE instance can
represent a pending name lock.

Test case added to lock_sync.test.

mysql-test/r/lock_sync.result

@@ -629,3 +629,30 @@ drop procedure p1;
 drop procedure p2;
 drop table t1, t2, t3, t4, t5, te;
 set @@global.concurrent_insert= @old_concurrent_insert;
+#
+# Bug#11763784 56541: ASSERTION TABLE->DB_STAT FAILED IN
+#                     SQL_BASE.CC::OPEN_TABLE() DURING I_S Q
+#
+DROP TABLE IF EXISTS t1;
+CREATE TABLE t1(a int);
+INSERT INTO t1 VALUES (1), (2);
+CREATE TRIGGER t1_bi BEFORE INSERT ON t1 FOR EACH ROW BEGIN END;
+# Connection con2
+SET DEBUG_SYNC= 'before_open_in_get_all_tables SIGNAL is_waits WAIT_FOR is_cont';
+# Sending:
+SELECT * FROM information_schema.table_constraints JOIN t1 ON table_name = a;
+# Connection con1
+SET DEBUG_SYNC= 'now WAIT_FOR is_waits';
+# Sending:
+DROP TRIGGER t1_bi;
+# Connection default
+# Wait until DROP TRIGGER is blocked, waiting for t1
+SET DEBUG_SYNC= 'now SIGNAL is_cont';
+# Connection con2
+# Reaping SELECT * FROM information_schema.table_constraints JOIN t1...
+CONSTRAINT_CATALOG	CONSTRAINT_SCHEMA	CONSTRAINT_NAME	TABLE_SCHEMA	TABLE_NAME	CONSTRAINT_TYPE	a
+# Connection con1
+# Reaping DROP TRIGGER t1_bi
+# Connection default
+DROP TABLE t1;
+SET DEBUG_SYNC= 'RESET';

mysql-test/t/lock_sync.test

@@ -862,6 +862,60 @@ disconnect con2;
 set @@global.concurrent_insert= @old_concurrent_insert;
 
 
+--echo #
+--echo # Bug#11763784 56541: ASSERTION TABLE->DB_STAT FAILED IN
+--echo #                     SQL_BASE.CC::OPEN_TABLE() DURING I_S Q
+--echo #
+
+--disable_warnings
+DROP TABLE IF EXISTS t1;
+--enable_warnings
+
+CREATE TABLE t1(a int);
+INSERT INTO t1 VALUES (1), (2);
+CREATE TRIGGER t1_bi BEFORE INSERT ON t1 FOR EACH ROW BEGIN END;
+
+connect (con1, localhost, root);
+--echo # Connection con2
+connect (con2, localhost, root);
+SET DEBUG_SYNC= 'before_open_in_get_all_tables SIGNAL is_waits WAIT_FOR is_cont';
+--echo # Sending:
+--send SELECT * FROM information_schema.table_constraints JOIN t1 ON table_name = a
+
+--echo # Connection con1
+connection con1;
+SET DEBUG_SYNC= 'now WAIT_FOR is_waits';
+--echo # Sending:
+--send DROP TRIGGER t1_bi
+
+--echo # Connection default
+connection default;
+--echo # Wait until DROP TRIGGER is blocked, waiting for t1
+let $wait_condition=
+  SELECT COUNT(*) = 1 FROM information_schema.processlist
+  WHERE state = "Waiting for table" AND
+        info = "DROP TRIGGER t1_bi";
+--source include/wait_condition.inc
+SET DEBUG_SYNC= 'now SIGNAL is_cont';
+
+--echo # Connection con2
+connection con2;
+--echo # Reaping SELECT * FROM information_schema.table_constraints JOIN t1...
+--reap
+
+--echo # Connection con1
+connection con1;
+--echo # Reaping DROP TRIGGER t1_bi
+--reap
+
+--echo # Connection default
+connection default;
+DROP TABLE t1;
+SET DEBUG_SYNC= 'RESET';
+disconnect con1;
+disconnect con2;
+
+
 # Check that all connections opened by test cases in this file are really
 # gone so execution of other tests won't be affected by their presence.
 --source include/wait_until_count_sessions.inc

sql/sql_base.cc

@@ -2798,10 +2798,9 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
                  ("Found table '%s.%s' with different refresh version",
                   table_list->db, table_list->table_name));
 
-      /* Ignore FLUSH, but not name locks! */
+      /* Ignore FLUSH and pending name locks, but not acquired name locks! */
       if (flags & MYSQL_LOCK_IGNORE_FLUSH && !table->open_placeholder)
       {
-        DBUG_ASSERT(table->db_stat);
         /* Force close at once after usage */
         thd->version= table->s->version;
         continue;