• Guilhem Bichot's avatar
    Fix for BUG#40661 "Maria: crash in embedded server (when detecting deadlock?)" · 255f8feb
    Guilhem Bichot authored
    bug is actually a weirdness in test system, so moving test portion into maria_notembedded.test
    
    mysql-test/suite/maria/r/maria.result:
      result update
    mysql-test/suite/maria/r/maria_notembedded.result:
      result update
    mysql-test/suite/maria/t/maria.test:
          Removing test portion into maria_notembedded.test. Explanation below.
          Running maria.test with --mem --embedded --valgrind I got:
          ==378== Invalid read of size 4
          ==378==    at 0x857C755: _lf_pinbox_real_free (lf_alloc-pin.c:342)
          ==378==    by 0x857C640: _lf_pinbox_free (lf_alloc-pin.c:267)
          ==378==    by 0x857D50C: ldelete (lf_hash.c:226)
          ==378==    by 0x857DBC1: lf_hash_delete (lf_hash.c:429)
          ==378==    by 0x8243D82: unlock_lock_and_free_resource
          (waiting_threads.c:676)
          ==378==    by 0x8244A79: wt_thd_release (waiting_threads.c:948)
          ==378==    by 0x83F301D: wt_thd_release_self (trnman.c:98)
          ==378==    by 0x83F3D49: trnman_end_trn (trnman.c:431)
          ==378==    by 0x837C437: ma_commit (ma_commit.c:60)
          ==378==    by 0x835F082: ha_maria::external_lock(THD*, int)
          (ha_maria.cc:2387)
          ==378==    by 0x84D1011: handler::ha_external_lock(THD*, int)
          (handler.cc:4433)
          ==378==    by 0x856DA92: unlock_external(THD*, st_table**, unsigned)
          (lock.cc:786)
          ==378==    by 0x856DD6F: mysql_unlock_tables(THD*, st_mysql_lock*)
          (lock.cc:389)
          ==378==    by 0x8274A57: close_thread_tables(THD*) (sql_base.cc:1307)
          ==378==    by 0x82ABEC3: unlock_locked_tables(THD*) (sql_parse.cc:99)
          ==378==    by 0x82B0BB3: mysql_execute_command(THD*)
          (sql_parse.cc:3372)
          ==378==  Address 0x5894a0c is 164 bytes inside a block of size 184
          free'd
          ==378==    at 0x40233FC: free (vg_replace_malloc.c:323)
          ==378==    by 0x823CF92: my_thread_end (my_thr_init.c:348)
          ==378==    by 0x8200FEE: mysql_thread_end (libmysql.c:250)
          ==378==    by 0x81A9487: send_one_query (mysqltest.c:535)
          ==378==    by 0x4050111: start_thread (in /lib/libpthread-2.5.so)
          ==378==    by 0x41A52ED: clone (in /lib/libc-2.5.so)
          
          (among other errors). The line where the invalid read happens is:
            if (available_stack_size(&pinbox, *pins->stack_ends_here) >
          alloca_size)
          and stack_ends_here was previously set here:
            el->stack_ends_here= & my_thread_var->stack_ends_here;
          The mysqltest "send" command, in embedded mode, is implemented this way
          (mysqltest.c:do_send_query()): a *new OS thread* is created in
          mysqltest, and does this:
          
            mysql_thread_init();
            VOID(mysql_send_query(&cn->mysql, cn->cur_query,
          cn->cur_query_len));
            mysql_thread_end();
          
          So, con_d "send insert t1 values (2)" creates a new OS thread, which
          gets a thread-specific data (mysql_thread_init()), then sends the
          query; in particular, this sets el->stack_ends_here to a pointer inside
          the thread-specific data (see my_thread_var above), that is, thd->pins
          depends on the thread-specific data.
          This sent "insert" blocks as expected, thread-specific data is free()d
          (my_thread_end() above), OS thread terminates.
          Then "default" connection runs "insert t1 values (3)"
          which blocks on the 3 already inserted by the con_d.
          This blocking (see waiting_threads.c) creates a WT_RESOURCE, which has,
          as owner, con_d's WT_THD.
          When con_d calls "unlock tables" (see stack trace), it wants to release
          this resource, which involves con_d's thd->pins, so it ends up reading
          stack_ends_here which points inside the freed thread-specific data =>
          Valgrind error, crashes...
          So this is an effect of having one single connection (con_d) for which
          two queries:
          send insert t1 values (2)
          unlock tables
          are done by different OS threads. That is indeed weird design of
          mysqltest, and it breaks on the dependency of lf_alloc-pin.c on
          thread-specific data. It is maybe already explained in those comments
          in lf_alloc-pin.c:
          "  It is assumed that pins belong to a THD and are not transferable
            between THD's (LF_PINS::stack_ends_here being a primary reason
            for this limitation)."
          "    It is assumed that pins belong to a thread and are not
          transferable
              between threads."
          
          In correct usage of libmysqld (no two queries sent for one connection
          by two threads), this problem would not happen, so I call it a
          deficiency of the test system.
    mysql-test/suite/maria/t/maria_notembedded.test:
      moving test portion into maria_notembedded.test
    255f8feb
maria.result 87.9 KB