MDEV-19273: Server crash in MDL_ticket::has_stronger_or_equal_type or Assertion `thd->mdl_context.is_lock_owner(MDL_key::TABLE, table->db.str, table->table_name.str, MDL_SHARED)' failed in mysql_rm_table_no_locks

Early report error in case of DROP SEQUENCE <non-sequence>

Do not use error variable for other purposes except error.

mysql-test/suite/sql_sequence/create.result

@@ -666,7 +666,7 @@ create temporary sequence s;
 drop temporary table s;
 create temporary table s (i int);
 drop temporary sequence s;
-ERROR 42S02: Unknown SEQUENCE: 'test.s'
+ERROR 42S02: 'test.s' is not a SEQUENCE
 drop table s;
 #
 # MDEV-15115 Assertion failure in CREATE SEQUENCE...ROW_FORMAT=REDUNDANT

mysql-test/suite/sql_sequence/create.test

@@ -489,7 +489,7 @@ drop table s;
 create temporary sequence s;
 drop temporary table s;
 create temporary table s (i int);
---error ER_UNKNOWN_SEQUENCES
+--error ER_NOT_SEQUENCE2
 drop temporary sequence s;
 drop table s;
 

mysql-test/suite/sql_sequence/other.result

@@ -300,4 +300,63 @@ update t1 set p_first_name='Yunxi' where p_id=1;
 drop view v2;
 drop table t1,t2;
 drop sequence s1;
+#
+# MDEV-19273:Server crash in MDL_ticket::has_stronger_or_equal_type or
+# Assertion `thd->mdl_context.is_lock_owner(MDL_key::TABLE,
+# table->db.str, table->table_name.str, MDL_SHARED)' failed
+# in mysql_rm_table_no_locks
+#
+CREATE TABLE t1 (a INT);
+CREATE TEMPORARY TABLE tmp (b INT);
+LOCK TABLE t1 READ;
+DROP SEQUENCE tmp;
+ERROR 42S02: 'test.tmp' is not a SEQUENCE
+DROP TEMPORARY SEQUENCE tmp;
+ERROR 42S02: 'test.tmp' is not a SEQUENCE
+DROP SEQUENCE t1;
+ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
+DROP TEMPORARY SEQUENCE t1;
+ERROR 42S02: Unknown SEQUENCE: 'test.t1'
+UNLOCK TABLES;
+DROP SEQUENCE t1;
+ERROR 42S02: 'test.t1' is not a SEQUENCE
+DROP TEMPORARY SEQUENCE t1;
+ERROR 42S02: Unknown SEQUENCE: 'test.t1'
+DROP TABLE t1;
+CREATE TABLE t (a INT);
+CREATE TEMPORARY TABLE s (f INT);
+CREATE SEQUENCE s;
+LOCK TABLE t WRITE;
+DROP SEQUENCE s;
+ERROR 42S02: 'test.s' is not a SEQUENCE
+DROP TEMPORARY SEQUENCE s;
+ERROR 42S02: 'test.s' is not a SEQUENCE
+UNLOCK TABLES;
+CREATE TEMPORARY SEQUENCE s;
+LOCK TABLE t WRITE;
+DROP TEMPORARY SEQUENCE s;
+UNLOCK TABLES;
+DROP TEMPORARY TABLE s;
+DROP SEQUENCE s;
+create table s(a INT);
+CREATE TEMPORARY TABLE s (f INT);
+LOCK TABLE t WRITE;
+DROP TEMPORARY TABLE s;
+CREATE TEMPORARY TABLE s (f INT);
+DROP TABLE s;
+DROP TABLE s;
+ERROR HY000: Table 's' was not locked with LOCK TABLES
+UNLOCK TABLES;
+DROP TABLE s;
+CREATE VIEW v1 as SELECT * FROM t;
+CREATE SEQUENCE s;
+DROP SEQUENCE IF EXISTS v1;
+Warnings:
+Note	4091	Unknown SEQUENCE: 'test.v1'
+DROP VIEW IF EXISTS s;
+Warnings:
+Note	4092	Unknown VIEW: 'test.s'
+DROP VIEW v1;
+DROP SEQUENCE s;
+DROP TABLE t;
 # End of 10.3 tests

mysql-test/suite/sql_sequence/other.test

@@ -315,4 +315,68 @@ drop view v2;
 drop table t1,t2;
 drop sequence s1;
 
+--echo #
+--echo # MDEV-19273:Server crash in MDL_ticket::has_stronger_or_equal_type or
+--echo # Assertion `thd->mdl_context.is_lock_owner(MDL_key::TABLE,
+--echo # table->db.str, table->table_name.str, MDL_SHARED)' failed
+--echo # in mysql_rm_table_no_locks
+--echo #
+
+CREATE TABLE t1 (a INT);
+CREATE TEMPORARY TABLE tmp (b INT);
+LOCK TABLE t1 READ;
+--error ER_NOT_SEQUENCE2
+DROP SEQUENCE tmp;
+--error ER_NOT_SEQUENCE2
+DROP TEMPORARY SEQUENCE tmp;
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+DROP SEQUENCE t1;
+--error ER_UNKNOWN_SEQUENCES
+DROP TEMPORARY SEQUENCE t1;
+UNLOCK TABLES;
+--error ER_NOT_SEQUENCE2
+DROP SEQUENCE t1;
+--error ER_UNKNOWN_SEQUENCES
+DROP TEMPORARY SEQUENCE t1;
+
+# Cleanup
+DROP TABLE t1;
+
+
+CREATE TABLE t (a INT);
+CREATE TEMPORARY TABLE s (f INT);
+CREATE SEQUENCE s;
+LOCK TABLE t WRITE;
+--error ER_NOT_SEQUENCE2
+DROP SEQUENCE s;
+--error ER_NOT_SEQUENCE2
+DROP TEMPORARY SEQUENCE s;
+UNLOCK TABLES;
+CREATE TEMPORARY SEQUENCE s;
+LOCK TABLE t WRITE;
+DROP TEMPORARY SEQUENCE s;
+UNLOCK TABLES;
+DROP TEMPORARY TABLE s;
+DROP SEQUENCE s;
+
+create table s(a INT);
+CREATE TEMPORARY TABLE s (f INT);
+LOCK TABLE t WRITE;
+DROP TEMPORARY TABLE s;
+CREATE TEMPORARY TABLE s (f INT);
+DROP TABLE s;
+--error ER_TABLE_NOT_LOCKED
+DROP TABLE s;
+UNLOCK TABLES;
+DROP TABLE s;
+
+CREATE VIEW v1 as SELECT * FROM t;
+CREATE SEQUENCE s;
+
+DROP SEQUENCE IF EXISTS v1;
+DROP VIEW IF EXISTS s;
+
+DROP VIEW v1;
+DROP SEQUENCE s;
+DROP TABLE t;
 --echo # End of 10.3 tests

sql/sql_table.cc

@@ -2314,8 +2314,11 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables, bool if_exists,
   {
     bool is_trans= 0;
     bool table_creation_was_logged= 0;
+    bool real_table= FALSE;
     LEX_CSTRING db= table->db;
     handlerton *table_type= 0;
+    // reset error state for this table
+    error= 0;
 
     DBUG_PRINT("table", ("table_l: '%s'.'%s'  table: %p  s: %p",
                          table->db.str, table->table_name.str,  table->table,
@@ -2331,9 +2334,35 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables, bool if_exists,
                   thd->find_temporary_table(table) &&
                   table->mdl_request.ticket != NULL));
 
-    if (table->open_type == OT_BASE_ONLY || !is_temporary_table(table) ||
+    if (table->open_type == OT_BASE_ONLY || !is_temporary_table(table))
-        (drop_sequence && table->table->s->table_type != TABLE_TYPE_SEQUENCE))
+      real_table= TRUE;
+    else if (drop_sequence &&
+            table->table->s->table_type != TABLE_TYPE_SEQUENCE)
+    {
+      was_table= (table->table->s->table_type == TABLE_TYPE_NORMAL);
+      was_view= (table->table->s->table_type == TABLE_TYPE_VIEW);
+      if (if_exists)
+      {
+        char buff[FN_REFLEN];
+        String tbl_name(buff, sizeof(buff), system_charset_info);
+        tbl_name.length(0);
+        tbl_name.append(&db);
+        tbl_name.append('.');
+        tbl_name.append(&table->table_name);
+        push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
+                            ER_NOT_SEQUENCE2, ER_THD(thd, ER_NOT_SEQUENCE2),
+                            tbl_name.c_ptr_safe());
+
+        /*
+          Our job is done here. This statement was added to avoid executing
+          unnecessary code farther below which in some strange corner cases
+          caused the server to crash (see MDEV-17896).
+        */
+        goto log_query;
+      }
       error= 1;
+      goto non_critical_err;
+    }
     else
     {
       table_creation_was_logged= table->table->s->table_creation_was_logged;
@@ -2342,29 +2371,28 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables, bool if_exists,
         error= 1;
         goto err;
       }
-      error= 0;
       table->table= 0;
     }
 
-    if ((drop_temporary && if_exists) || !error)
+    if ((drop_temporary && if_exists) || !real_table)
     {
       /*
         This handles the case of temporary tables. We have the following cases:
 
           . "DROP TEMPORARY" was executed and a temporary table was affected
-          (i.e. drop_temporary && !error) or the if_exists was specified (i.e.
+          (i.e. drop_temporary && !real_table) or the
-          drop_temporary && if_exists).
+          if_exists was specified (i.e. drop_temporary && if_exists).
 
           . "DROP" was executed but a temporary table was affected (.i.e
-          !error).
+          !real_table).
       */
       if (!dont_log_query && table_creation_was_logged)
       {
         /*
-          If there is an error, we don't know the type of the engine
+          If there is an real_table, we don't know the type of the engine
           at this point. So, we keep it in the trx-cache.
         */
-        is_trans= error ? TRUE : is_trans;
+        is_trans= real_table ? TRUE : is_trans;
         if (is_trans)
           trans_tmp_table_deleted= TRUE;
         else
@@ -2391,7 +2419,7 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables, bool if_exists,
         is no need to proceed with the code that tries to drop a regular
         table.
       */
-      if (!error) continue;
+      if (!real_table) continue;
     }
     else if (!drop_temporary)
     {
@@ -2407,7 +2435,6 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables, bool if_exists,
                                         reg_ext, 0);
     }
     DEBUG_SYNC(thd, "rm_table_no_locks_before_delete_table");
-    error= 0;
     if (drop_temporary ||
         (ha_table_exists(thd, &db, &alias, &table_type, &is_sequence) == 0 &&
          table_type == 0) ||
@@ -2447,6 +2474,11 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables, bool if_exists,
       {
         non_tmp_error = (drop_temporary ? non_tmp_error : TRUE);
         error= 1;
+        /*
+          non critical error (only for this table), so we continue.
+          Next we write it to wrong_tables and continue this loop
+          The same as "goto non_critical_err".
+        */
       }
     }
     else
@@ -2540,7 +2572,7 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables, bool if_exists,
       }
       non_tmp_error|= MY_TEST(error);
     }
-
+non_critical_err:
     if (error)
     {
       if (wrong_tables.length())