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  1. MariaDB Server
  2. MDEV-8644

Using a UDF in a virtual column causes a crash when stopping the server

Details

    Description

      Because MariaDB does not accept a constant virtual column (other DBMS's do) I was obliged to write the noconst UDF as:

      /***********************************************************************/
      		 
      /*  Returns its argument saying it is not a constant.                  */
      		 
      /***********************************************************************/
      		 
      my_bool noconst_init(UDF_INIT *initid, UDF_ARGS *args, char *message)
      		 
      {
      		 
      	if (args->arg_count != 1 || args->arg_type[0] != STRING_RESULT) {
      		 
      		strcpy(message, "noconst unique argument must be a string");
      		 
      		return true;
      		 
      	} // endif arg
      		 
       
      		 
      	initid->const_item = false;    // The trick!
      		 
      	return false;
      		 
      } // end of noconst_init
      		 
       
      		 
      char *noconst(UDF_INIT *initid, UDF_ARGS *args, char *result,
      		 
      	unsigned long *res_length, char *, char *)
      		 
      {
      		 
      	return args->args[0];
      		 
      } // end of noconst

      Now, creating the table t1, inserting one line to it and displaying it does work:

      MariaDB [test]> create table t1 (
      		 
          -> n int key not null auto_increment,
      		 
          -> msg char(20) as (noconst('Hello World')) virtual);
      		 
      Query OK, 0 rows affected (0.06 sec)
      		 
       
      		 
      MariaDB [test]> insert into t1() values();
      		 
      Query OK, 1 row affected (0.01 sec)
      		 
       
      		 
      MariaDB [test]> select * from t1;
      		 
      +---+-------------+
      		 
      | n | msg         |
      		 
      +---+-------------+
      		 
      | 1 | Hello World |
      		 
      +---+-------------+
      		 
      1 row in set (0.00 sec)

      However, later on when stopping the server a crash occurs in the function:

      void udf_handler::cleanup()
      		 
      {
      		 
        if (!not_original)
      		 
        {
      		 
          if (initialized)
      		 
          {
      		 
            if (u_d->func_deinit != NULL)
      		 
            {
      		 
              Udf_func_deinit deinit= u_d->func_deinit;
      		 
              (*deinit)(&initid);
      		 
            }
      		 
            free_udf(u_d);
      		 
            initialized= FALSE;
      		 
          }
      		 
          if (buffers)				// Because of bug in ecc
      		 
            delete [] buffers;
      		 
          buffers= 0;
      		 
        }
      		 
      }

      See the attach udf_crash.log.
      The same kind of crash occurs with different other UDF's.

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          elenst Elena Stepanova added a comment -

          That's a surprise it works at all, documentation says UDFs are not allowed for virtual columns.

          bertrandop,
          Could you please attach the whole c file with your UDF function? It will be faster than me creating missing parts.

          elenst Elena Stepanova added a comment - That's a surprise it works at all, documentation says UDFs are not allowed for virtual columns. bertrandop , Could you please attach the whole c file with your UDF function? It will be faster than me creating missing parts.
          bertrandop Olivier Bertrand added a comment -

          Done.

          bertrandop Olivier Bertrand added a comment - Done.
          elenst Elena Stepanova added a comment -

          Stack trace from 5.5 commit 29ac245dd04c5416d57a90b0ab3c4d08cbc4d723

          		 
          #3  <signal handler called>
          		 
          #4  0x00000000008500ae in udf_handler::cleanup (this=0x7f11c2875968) at 5.5/sql/item_func.cc:3454
          		 
          #5  0x00000000008514e0 in Item_udf_func::cleanup (this=0x7f11c28758a0) at 5.5/sql/item_func.cc:3766
          		 
          #6  0x00000000006073a1 in Item::delete_self (this=0x7f11c28758a0) at 5.5/sql/item.h:1434
          		 
          #7  0x000000000060162f in Query_arena::free_items (this=0x7f11c2874bf8) at 5.5/sql/sql_class.cc:3164
          		 
          #8  0x00000000006fcf32 in closefrm (table=0x7f11c2828e60, free_share=true) at 5.5/sql/table.cc:2773
          		 
          #9  0x00000000005d4378 in intern_close_table (table=0x7f11c2828e60) at 5.5/sql/sql_base.cc:929
          		 
          #10 0x00000000005d43e5 in free_cache_entry (table=0x7f11c2828e60) at 5.5/sql/sql_base.cc:952
          		 
          #11 0x00000000005d4763 in close_cached_tables (thd=0x0, tables=0x0, wait_for_refresh=false, timeout=31536000) at 5.5/sql/sql_base.cc:1059
          		 
          #12 0x00000000005d3111 in table_def_start_shutdown () at 5.5/sql/sql_base.cc:410
          		 
          #13 0x0000000000586faf in clean_up (print_message=true) at 5.5/sql/mysqld.cc:1822
          		 
          #14 0x0000000000586d9e in unireg_end () at 5.5/sql/mysqld.cc:1735
          		 
          #15 0x0000000000586cc0 in kill_server (sig_ptr=0x0) at 5.5/sql/mysqld.cc:1663
          		 
          #16 0x0000000000586cdd in kill_server_thread (arg=0x7f11ed3b9e98) at 5.5/sql/mysqld.cc:1686
          		 
          #17 0x00007f11ecfaab50 in start_thread (arg=<optimized out>) at pthread_create.c:304
          		 
          #18 0x00007f11eb26095d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112

          elenst Elena Stepanova added a comment - Stack trace from 5.5 commit 29ac245dd04c5416d57a90b0ab3c4d08cbc4d723 #3 <signal handler called> #4 0x00000000008500ae in udf_handler::cleanup (this=0x7f11c2875968) at 5.5/sql/item_func.cc:3454 #5 0x00000000008514e0 in Item_udf_func::cleanup (this=0x7f11c28758a0) at 5.5/sql/item_func.cc:3766 #6 0x00000000006073a1 in Item::delete_self (this=0x7f11c28758a0) at 5.5/sql/item.h:1434 #7 0x000000000060162f in Query_arena::free_items (this=0x7f11c2874bf8) at 5.5/sql/sql_class.cc:3164 #8 0x00000000006fcf32 in closefrm (table=0x7f11c2828e60, free_share=true) at 5.5/sql/table.cc:2773 #9 0x00000000005d4378 in intern_close_table (table=0x7f11c2828e60) at 5.5/sql/sql_base.cc:929 #10 0x00000000005d43e5 in free_cache_entry (table=0x7f11c2828e60) at 5.5/sql/sql_base.cc:952 #11 0x00000000005d4763 in close_cached_tables (thd=0x0, tables=0x0, wait_for_refresh=false, timeout=31536000) at 5.5/sql/sql_base.cc:1059 #12 0x00000000005d3111 in table_def_start_shutdown () at 5.5/sql/sql_base.cc:410 #13 0x0000000000586faf in clean_up (print_message=true) at 5.5/sql/mysqld.cc:1822 #14 0x0000000000586d9e in unireg_end () at 5.5/sql/mysqld.cc:1735 #15 0x0000000000586cc0 in kill_server (sig_ptr=0x0) at 5.5/sql/mysqld.cc:1663 #16 0x0000000000586cdd in kill_server_thread (arg=0x7f11ed3b9e98) at 5.5/sql/mysqld.cc:1686 #17 0x00007f11ecfaab50 in start_thread (arg=<optimized out>) at pthread_create.c:304 #18 0x00007f11eb26095d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112
          serg Sergei Golubchik added a comment -

          I cannot repeat this. elenst, could you please show a complete test case?

          serg Sergei Golubchik added a comment - I cannot repeat this. elenst , could you please show a complete test case?
          elenst Elena Stepanova added a comment -

          I do the following:

          • build the attached noconst.c as g++ -shared -o noconst.so noconst.c -I/home/elenst/git/5.5/sql -I/home/elenst/git/5.5/include
          • start the debug server with noconst.so in the plugin dir;
          • run 

            CREATE FUNCTION noconst RETURNS STRING SONAME 'noconst.so';
            		 
            create table t1 (n int key not null auto_increment,  msg char(11) as (noconst('Hello World')) virtual);
            		 
            insert into t1() values();
            		 
            select * from t1;

          • shutdown server;
            => observe the crash.

          Reproducible on 5.5 commit 13ad179c96ee8c8c4043806b8575c851e3676f0d

          -

          elenst Elena Stepanova added a comment - I do the following: build the attached noconst.c as g++ -shared -o noconst.so noconst.c -I/home/elenst/git/5.5/sql -I/home/elenst/git/5.5/include start the debug server with noconst.so in the plugin dir; run CREATE FUNCTION noconst RETURNS STRING SONAME 'noconst.so'; create table t1 (n int key not null auto_increment, msg char(11) as (noconst('Hello World')) virtual); insert into t1() values(); select * from t1; shutdown server; => observe the crash. Reproducible on 5.5 commit 13ad179c96ee8c8c4043806b8575c851e3676f0d -
          bertrandop Olivier Bertrand added a comment -

          Does this mean that UDFs are no more banned from virtual columns?
          If so, it should be documented.

          bertrandop Olivier Bertrand added a comment - Does this mean that UDFs are no more banned from virtual columns? If so, it should be documented.
          serg Sergei Golubchik added a comment -

          They were not banned, were they? If they were banned, one would not be able to create a virtual column with a UDF in the first place.

          serg Sergei Golubchik added a comment - They were not banned, were they? If they were banned, one would not be able to create a virtual column with a UDF in the first place.
          elenst Elena Stepanova added a comment - - edited

          serg, it was the point of my initial comment: the documentation says they cannot be used, while in fact they can.
          I don't know whether they had ever been (or supposed to be) forbidden, or it is just a documentation mistake.

          elenst Elena Stepanova added a comment - - edited serg , it was the point of my initial comment: the documentation says they cannot be used, while in fact they can. I don't know whether they had ever been (or supposed to be) forbidden, or it is just a documentation mistake.

          People

            serg Sergei Golubchik
            bertrandop Olivier Bertrand
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              Updated:
              Resolved:

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