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From Ruediger Pluem <rpl...@apache.org>
Subject Re: svn commit: r646582 - /httpd/httpd/trunk/modules/ldap/util_ldap.c
Date Thu, 10 Apr 2008 20:00:50 GMT
On 10.04.2008 18:11, Brad Nicholes wrote:
>>>> On 4/10/2008 at 12:12 AM, in message <47FDAFE4.4070806@apache.org>,
> Ruediger
> Pluem <rpluem@apache.org> wrote:
>> On 10.04.2008 00:49, bnicholes@apache.org wrote:
>>> Author: bnicholes Date: Wed Apr  9 15:49:31 2008 New Revision:
> 646582
>>> URL: http://svn.apache.org/viewvc?rev=646582&view=rev Log: Move the
>>> initialization of rebind to the post_config handler so that it is
> done 
>> during
>>> the actual module load stage rather than the preload stage.  If done
> during
>>> the preload stage, the pool passed into the initialization function
> will be
>>> cleared and all allocations will be freed.
>> But isn't it the pconf pool in both cases? Currently I cannot follow
> this 
>> argument. Mind to explain in more detail?
>>
>> Regards
>>
>> RĂ¼diger
> 
> What is happening is that when httpd is invoked, the first thing it
> does is preload all of the modules to make sure that everything works. 
> The preload of the modules also calls the util_ldap_create_config()
> which subsequently calls apr_ldap_rebind_init().  In
> apr_ldap_rebind_init() some allocations are done.  Actually a thread
> mutex is created against the pool that was passed in.  In addition, the
> clean up of the mutex was tied to the pool and the rebind init function
> also assigned to a global static variable, the mutex handle.  Then when
> the preload stage is complete, it clears the memory pool which also
> causes the mutex to be destroy.  However the mutex handle, which is now
> bogus, is still assigned to the global static variable.  Finally the
> real module loading stage occurs and util_ldap_create_config() and
> apr_ldap_rebind_init() are called again.  Only this time the
> apr_ldap_rebind_init() sees that the mutex global static variable is no
> longer NULL so it doesn't bother to recreate the mutex leaving a bogus
> value in the static variable.  When an ldap authentication occurs later
> and tries to use the bogus mutex handle, at least on NetWare, the code
> segfaults. 
> 
> The change was simply moving the init of the rebind functionality to a
> location in the code where everything else is initialized and is also
> protected so that the initialization only happens during the real module
> load stage rather than the preload stage.

Thanks for explaining. I now understand why it is bad to call 
apr_ldap_rebind_init twice, but I still do not get how your change helps 
avoiding this as the post_config hook is also called twice and the pconf
pool that is used for apr_ldap_rebind_init is cleaned up in between.
Sorry for being persistent on this, but care to explain where my thoughts
are wrong here?
In other parts of the code these situations are normally solved by something
like if (staticvar++) {} with staticvar being an static global int initialized 
with 0.

Regards

RĂ¼diger


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