linux-kernel - Re: eeepc_hotkey rmmod issues

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Date:	Wed, 29 Jul 2009 13:17:12 +0100
From:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
To:	Corentin Chary <corentin.chary@...il.com>
CC:	Pekka Enberg <penberg@...helsinki.fi>, linux-kernel@...r.kernel.org
Subject: Re: eeepc_hotkey rmmod issues

Corentin Chary wrote:
> On Wed, Jul 29, 2009 at 2:02 PM, Alan
> Jenkins<sourcejedi.lkml@...glemail.com> wrote:
>   
>> On 7/29/09, Corentin Chary <corentin.chary@...il.com> wrote:
>>     
>>> On Wed, Jul 29, 2009 at 12:01 PM, Alan
>>> Jenkins<sourcejedi.lkml@...glemail.com> wrote:
>>>       
>>>> On 7/28/09, Corentin Chary <corentin.chary@...il.com> wrote:
>>>>         
>>>>> On Tue, Jul 28, 2009 at 9:19 PM, Alan
>>>>> Jenkins<sourcejedi.lkml@...glemail.com> wrote:
>>>>>           
>>>>>> But we should still fix the underlying problem.  It sounds like
>>>>>> there's a narrow danger window on module unload.  And it's still there
>>>>>> in 2.6.31-rc4:
>>>>>>
>>>>>> 1019 static void eeepc_rfkill_exit(void)
>>>>>> 1020 {
>>>>>> 1021         eeepc_unregister_rfkill_notifier("\\_SB.PCI0.P0P6");
>>>>>> 1022         eeepc_unregister_rfkill_notifier("\\_SB.PCI0.P0P7");
>>>>>> 1023         if (ehotk->wlan_rfkill)
>>>>>> 1024                 rfkill_unregister(ehotk->wlan_rfkill);
>>>>>>
>>>>>> Really we need to perform these unregistrations "at the same time".
>>>>>> The rfkill device relies on the notifier, but the notifier callback
>>>>>> also uses the rfkill device.  I guess we will need to a mutex to
>>>>>> synchronize unregistration (and registration).
>>>>>>             
>>>>> I think 2.6.31 is ok,
>>>>>           
>>>>> In 2.6.30, we called eeepc_unregister_rfkill_notifier after
>>>>> rfkill_free, which was an error because
>>>>> the notifier callback uses the rfkill device.
>>>>>           
>>>> Ok.  I don't see how that causes Luciano's errors.  So I guess he was
>>>> right to blame the wireless driver.
>>>>         
>>> If he was using 2.6.30, then :
>>> eeepc_unregister_rfkill_notifier() was called after rfkill_unregister()
>>> And the callback was still registered after rfkill_unregister(), *Ooops*
>>>
>>> In 2.6.31 we first unregister the callback, and then rfkill, so rmmod
>>> should works.
>>>
>>>       
>>>>> But I believe that the rfkill device can work without the notifier
>>>>> (which is an acpi notifier).
>>>>>           
>>>> I don't think it can.
>>>>
>>>> If the rfkill device is set to "soft blocked", the pci device is
>>>> removed.  If the acpi notifier is not called, the pci driver (e.g.
>>>> ath5k) won't realise the device is gone.  The network device (e.g.
>>>> wlan0) will remain present, but it won't work.
>>>>         
>>> Hum, there is a misunderstanding here. What I mean is : I think
>>> eeepc_rfkill_exit(void) is ok in 2.6.31 (Luciano used 2.6.30).
>>>
>>> And eeepc_rfkill_exit() is only called on rmmod eeepc-laptop
>>>
>>> Commit 7de39389d8f61aa517ce2a8b4d925acc62696ae5 did a lot of
>>> change in rfkill code.
>>>
>>>       
>>>> So I believe there's a circular dependency which we need to resolve.
>>>> Would you like me to write a patch for it?
>>>>         
>>> It's possible that I miss the issue here, so go ahead :)
>>>       
>> Thanks :)
>>
>> Here is a test case to show the race I am talking about
>>
>> diff --git a/drivers/platform/x86/eeepc-laptop.c b/drivers/platform/x86/eeepc-laptop.c
>> index ec560f1..c478db5 100644
>> --- a/drivers/platform/x86/eeepc-laptop.c
>> +++ b/drivers/platform/x86/eeepc-laptop.c
>> @@ -1020,6 +1020,17 @@ static void eeepc_rfkill_exit(void)
>>  {
>>        eeepc_unregister_rfkill_notifier("\\_SB.PCI0.P0P6");
>>        eeepc_unregister_rfkill_notifier("\\_SB.PCI0.P0P7");
>> +
>> +       //
>> +       // Simulated error
>> +       // Imagine that userspace set the wifi to "soft blocked" at this exact moment
>> +       // (or the wireless toggle key was pressed)
>> +       //
>> +       // The PCI device will disappear, but we will not see any notification
>> +       //
>> +       set_acpi(CM_ASL_WLAN, 0);
>> +       rfkill_set_sw_state(ehotk->wlan_rfkill, true);
>> +
>>        if (ehotk->wlan_rfkill)
>>                rfkill_unregister(ehotk->wlan_rfkill);
>>        if (ehotk->bluetooth_rfkill)
>>
>>
>>
>> If you unload eeepc-laptop with this simulated race, the wireless
>> interface stays around but stops working.
>>
>> [  191.391155] ath5k phy0: can't reset hardware (-5)
>> [  191.432983] ath5k phy0: failed to wakeup the MAC Chip
>> [  196.940835] __ratelimit: 21 callbacks suppressed
>>
>> Alan
>>
>>     
>
> Indeed :) . Let's serialize that. Do you want me to do it ?
> Thanks,
>   

It's ok, I'm already working on a fix.

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