MDEV-24929 Server crash in thr_multi_unlock or in get_schema_tables_result

This was caused by two different bugs:
1) Information_schema tables where not locked by lock_tables, but
   get_lock_data() was not filtering these out. This caused a crash when
   mysql_unlock_some_tables() tried to unlock tables early, including
   not locked information schema tables.

Fixed by not locking SYSTEM_TMP_TABLES

2) In some cases the optimizer will notice that we do not need to read
   the information_schema tables at all. In this case
   join_tab->read_record is not set, which caused a crash in
   get_schema_tables_result()

Fixed by ignoring const tables in get_schema_tables_result()

mysql-test/main/information_schema.result

@@ -2303,5 +2303,18 @@ group by f;
 f
 drop table t1;
 #
+# MDEV-24929 Server crash in thr_multi_unlock or in
+# get_schema_tables_result upon select from I_S with joins
+#
+CREATE TABLE t1 (a TIMESTAMP, KEY (a));
+INSERT INTO t1 VALUES ('2012-12-12'),('2021-11-11');
+SELECT count(*) FROM t1 AS t1a LEFT JOIN (t1 AS t1b JOIN INFORMATION_SCHEMA.ROUTINES) ON (t1b.a IS NULL);
+count(*)
+2
+SELECT count(*) FROM t1 AS t1a LEFT JOIN (t1 AS t1b JOIN INFORMATION_SCHEMA.PROFILING) ON (t1b.a IS NULL);
+count(*)
+2
+DROP TABLE t1;
+#
 # End of 10.3 tests
 #

mysql-test/main/information_schema.test

@@ -2034,6 +2034,16 @@ inner join t1 on f=i.column_name
 group by f;
 drop table t1;
 
+--echo #
+--echo # MDEV-24929 Server crash in thr_multi_unlock or in
+--echo # get_schema_tables_result upon select from I_S with joins
+--echo #
+
+CREATE TABLE t1 (a TIMESTAMP, KEY (a));
+INSERT INTO t1 VALUES ('2012-12-12'),('2021-11-11');
+SELECT count(*) FROM t1 AS t1a LEFT JOIN (t1 AS t1b JOIN INFORMATION_SCHEMA.ROUTINES) ON (t1b.a IS NULL);
+SELECT count(*) FROM t1 AS t1a LEFT JOIN (t1 AS t1b JOIN INFORMATION_SCHEMA.PROFILING) ON (t1b.a IS NULL);
+DROP TABLE t1;
 --echo #
 --echo # End of 10.3 tests
 --echo #

sql/lock.cc

@@ -727,6 +727,9 @@ static int unlock_external(THD *thd, TABLE **table,uint count)
            - GET_LOCK_STORE_LOCKS : Store lock info in TABLE
            - GET_LOCK_SKIP_SEQUENCES : Ignore sequences (for temporary unlock)
            - GET_LOCK_ON_THD      : Store lock in thd->mem_root
+
+  Temporary tables are not locked (as these are single user), except for
+  TRANSACTIONAL_TMP_TABLES as locking is needed to handle transactions.
 */
 
 MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table_ptr, uint count, uint flags)
@@ -743,8 +746,8 @@ MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table_ptr, uint count, uint flags)
   {
     TABLE *t= table_ptr[i];
     
-    if (t->s->tmp_table != NON_TRANSACTIONAL_TMP_TABLE && 
-        t->s->tmp_table != INTERNAL_TMP_TABLE &&
+    if ((likely(!t->s->tmp_table) ||
+         (t->s->tmp_table == TRANSACTIONAL_TMP_TABLE)) &&
         (!(flags & GET_LOCK_SKIP_SEQUENCES) || t->s->sequence == 0))
     {
       lock_count+= t->file->lock_count();
@@ -772,13 +775,13 @@ MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table_ptr, uint count, uint flags)
 
   for (i=0 ; i < count ; i++)
   {
-    TABLE *table;
+    TABLE *table= table_ptr[i];
     enum thr_lock_type lock_type;
     THR_LOCK_DATA **locks_start;
-    table= table_ptr[i];
-    if (table->s->tmp_table == NON_TRANSACTIONAL_TMP_TABLE ||
-        table->s->tmp_table == INTERNAL_TMP_TABLE ||
-        ((flags & GET_LOCK_SKIP_SEQUENCES) && table->s->sequence))
+
+    if (!((likely(!table->s->tmp_table) ||
+           (table->s->tmp_table == TRANSACTIONAL_TMP_TABLE)) &&
+          (!(flags & GET_LOCK_SKIP_SEQUENCES) || table->s->sequence == 0)))
       continue;
     lock_type= table->reginfo.lock_type;
     DBUG_ASSERT(lock_type != TL_WRITE_DEFAULT && lock_type != TL_READ_DEFAULT);

sql/sql_show.cc

@@ -8837,6 +8837,16 @@ bool get_schema_tables_result(JOIN *join,
       if (table_list->schema_table->fill_table == 0)
         continue;
 
+      /*
+        Do not fill in tables thare are marked as JT_CONST as these will never
+        be read and they also don't have a tab->read_record.table set!
+        This can happen with queries like
+        SELECT * FROM t1 LEFT JOIN (t1 AS t1b JOIN INFORMATION_SCHEMA.ROUTINES)
+        ON (t1b.a IS NULL);
+      */
+      if (tab->type == JT_CONST)
+        continue;
+
       /* skip I_S optimizations specific to get_all_tables */
       if (lex->describe &&
           (table_list->schema_table->fill_table != get_all_tables))