[asterisk-dev] [Code Review]: Make ast_unload_resource actually remove the module from the module list when it is unloaded

[wdoekes]

> On Feb. 22, 2012, 1:11 p.m., wdoekes wrote:
> > /trunk/res/res_calendar.c, lines 1811-1814
> > <https://reviewboard.asterisk.org/r/1752/diff/2/?file=24509#file24509line1811>
> >
> >     If it's now not possible to unload res_calendar before unloading those that depend on it, shouldn't this be replaced with an assert(AST_LIST_EMPTY(&techs)) ?
> 
> Terry Wilson wrote:
>     Bah. Indeed. The whole point originally was to be able to unload res_calendar and the dependent modules with "module unload res_calendar.so". Oh, well. At least this makes it obvious why it isn't unloading in that case and still allows it to shut down properly.
> 
> Terry Wilson wrote:
>     Actually, you can still successfully unload all of the modules with "module unload -h res_calendar.so" so I'll just leave this in.

successfully isn't the first word that springs to mind.

*CLI> module unload -h res_calendar
[Feb 22 22:18:30] WARNING[15761]: loader.c:535 ast_unload_resource: Warning:  Forcing removal of module 'res_calendar' with use count 2
WARNING: Freeing unused memory at 0x7f9ea4548b88, in __ast_module_user_remove of loader.c, line 231
WARNING: Freeing unused memory at 0x7f9ea4548668, in __ast_module_user_remove of loader.c, line 231
Unloaded res_calendar


- wdoekes


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On Feb. 22, 2012, 12:12 p.m., Terry Wilson wrote:
> 
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> 
> (Updated Feb. 22, 2012, 12:12 p.m.)
> 
> 
> Review request for Asterisk Developers.
> 
> 
> Summary
> -------
> 
> res_calendar calls ast_unload_resource for the related tech modules when it is unloaded. If this happens through a 'core stop gracefully', then it will be unloading the tech modules that are already in the list that is being traversed (supposedly safely) for unloading, eventually causing a double free. The problem seems to be that ast_unload_resource, while it calls the unload() callback function for the module, does not actually unlink the module from the list of modules. So the AST_LIST_TRAVERSE_SAFE_BEGIN {} still iterates over the unloaded module.
> 
> This patch causes ast_unload_resource to call AST_LIST_REMOVE on successfully unloaded modules.
> 
> 
> Diffs
> -----
> 
>   /trunk/include/asterisk/calendar.h 356213 
>   /trunk/main/loader.c 356213 
>   /trunk/res/res_calendar.c 356213 
> 
> Diff: https://reviewboard.asterisk.org/r/1752/diff
> 
> 
> Testing
> -------
> 
> Scenario: Start Asterisk with res_calendar and assorted calendar tech modules loaded. Run 'core stop gracefully'.
> Before patch: Crash.
> After patch: No crash.
> 
> 
> Thanks,
> 
> Terry
> 
>

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