Re: bk commit into 5.0 tree (aelkin:1.2526) BUG#26000

[Mats Kindahl]

Hi Andrei!

Comments below.

Just my few cents,
Mats Kindahl

Andrei Elkin wrote:
> Below is the list of changes that have just been committed into a local
> 5.0 repository of elkin. When elkin does a push these changes will
> be propagated to the main repository and, within 24 hours after the
> push, to the public repository.
> For information on how to access the public repository
> see http://dev.mysql.com/doc/mysql/en/installing-source-tree.html
>
> ChangeSet@stripped, 2007-09-26 21:59:17+02:00, aelkin@stripped +1 -0
>   Bug #26000 SHOW SLAVE STATUS can crash mysqld during shutdown process
>   
>   active_mi has been reset (shutdown) at the time of quering with 
>   SHOW SLAVE STATUS so that 
>   at handling of SHOW an attempt to read its members segfaults.
>   
>   Fixed with checking the value of active_mi before to call show_master_info()
>   Merely send_ok() is invoked when active_mi does not exist.
>   A test can not be easiely written.
>   
>   Notice, there are more analogical cases in the code which require a similar
>   treatment (to be reported as a bug separately). 
>
>   sql/sql_parse.cc@stripped, 2007-09-26 21:59:11+02:00, aelkin@stripped +10 -1
>     Ignore reporting and send only OK if master info struct has been destoyed.
>     As this must be at shutdown merely a warning is sent to the client.
>
> diff -Nrup a/sql/sql_parse.cc b/sql/sql_parse.cc
> --- a/sql/sql_parse.cc	2007-08-05 05:53:13 +02:00
> +++ b/sql/sql_parse.cc	2007-09-26 21:59:11 +02:00
> @@ -2844,7 +2844,16 @@ mysql_execute_command(THD *thd)
>      if (check_global_access(thd, SUPER_ACL | REPL_CLIENT_ACL))
>        goto error;
>      pthread_mutex_lock(&LOCK_active_mi);
> -    res = show_master_info(thd,active_mi);
> +    if (active_mi != NULL)
>   

This won't solve the bug. It just moves the sweet spot to just after the 
"if" above.

To fix the problem, it is necessary to ensure that all read and writes 
to the active_mi or the object that it points to is protected by the 
LOCK_active_mi mutex.

> +    {
> +      res = show_master_info(thd, active_mi);
> +    }
> +    else
> +    {
> +      push_warning(thd, MYSQL_ERROR::WARN_LEVEL_WARN, 0,
> +                   "the master info structure does not exist");
> +      send_ok(thd);
> +    }
>      pthread_mutex_unlock(&LOCK_active_mi);
>      break;
>    }
>
>   


-- 
Mats Kindahl
Lead Software Developer
Replication Team
MySQL AB, www.mysql.com