[pulseaudio-discuss] [PATCH v5 39/39] bluetooth: Revive module-bluetooth-discover

[João Paulo Rechi Vita]

On Wed, Oct 9, 2013 at 12:26 PM, João Paulo Rechi Vita
<jprvita at gmail.com> wrote:
> On Tue, Oct 8, 2013 at 12:15 PM, Tanu Kaskinen
> <tanu.kaskinen at linux.intel.com> wrote:
>> On Tue, 2013-10-08 at 11:19 -0300, João Paulo Rechi Vita wrote:
>>> On Sun, Sep 29, 2013 at 1:39 PM, Tanu Kaskinen
>>> <tanu.kaskinen at linux.intel.com> wrote:
>>> > On Tue, 2013-09-24 at 19:45 -0300, jprvita at gmail.com wrote:
>>> >> +void pa__done(pa_module* m) {
>>> >> +    struct userdata *u;
>>> >> +
>>> >> +    pa_assert(m);
>>> >> +
>>> >> +    if (!(u = m->userdata))
>>> >> +        return;
>>> >> +
>>> >> +    if (u->bluez5_module)
>>> >> +        pa_module_unload(m->core, u->bluez5_module, true);
>>> >> +
>>> >> +    if (u->bluez4_module)
>>> >> +        pa_module_unload(m->core, u->bluez4_module, true);
>>> >
>>> > This crashes when shutting down the daemon, because when the daemon
>>> > unloads all modules, module-bluez*-discover gets unloaded before
>>> > module-bluetooth-discover, so the y->bluez5_module and u->bluez4_module
>>> > pointers become stale. I see two ways of fixing this: add a hook that is
>>> > fired when modules are unloaded and use that hook in
>>> > module-bluetooth-discover to drop the reference to the unloaded module,
>>> > or unload module-bluetooth-discover immediately after loading
>>> > module-bluez5-discover and module-bluez4-discover. The second solution
>>> > is of course much simpler, but I proposed that already earlier, and you
>>> > didn't like that.
>>> >
>>>
>>> It doesn't crash (and that's what I'm experiencing here) because
>>> pa_module_unload() will look for that module pointer in its internal
>>> hash of modules before trying to unload it. I agree we are left with a
>>> stale pointer, but as long as we don't dereference it, we should be
>>> fine.
>>
>> pa_module_unload() dereferences the pointer already before
>>
>>     if (!(m = pa_idxset_remove_by_data(c->modules, m, NULL)))
>>         return;
>>
>> which I think you are referring to as the safeguard. The line that
>> crashes is this:
>>
>>     if (m->core->disallow_module_loading && !force)
>>

Hum, another thing came to my mind: pa_module_unload() also receives
the pa_core pointer through its arguments, why not use it in the check
for disallow_module_loading? Like this:

if (c->disallow_module_loading && !force)

-- 
João Paulo Rechi Vita
http://about.me/jprvita