Re: [Patch v4 14/16] x86, irq: Introduce helper to check whether an IOAPIC has been registered

[Jiang Liu <jiang.liu@linux.intel.com>]

On 2014/9/11 4:08, Thomas Gleixner wrote:
> On Wed, 10 Sep 2014, Jiang Liu wrote:
>> On 2014/9/9 20:37, Thomas Gleixner wrote:
>>>> +	ret  = mp_ioapic_registered(gsi_base);
>>>> +	up_write(&acpi_ioapic_rwsem);
>>>> +
>>>> +	return ret;
>>>> +}
>>>
>>> So I assume that this is for a particular caller in the apci ioapic
>>> hotplug code and that call site has its own serialization. Otherwise
>>> the return value is not protected at all.
>>>
>>> Please add a Docbook comment to that function, and document the
>>> locking rules as thats pretty non obvious.
>> How about this comments about locking rules?
>> /*
>>  * Locks related to IOAPIC hotplug
>>  * Hotplug side:
>>  *      ->lock_device_hotplug() //device_hotplug_lock
>>  *              ->acpi_ioapic_rwsem
>>  *                      ->ioapic_lock
>>  * Interrupt mapping side:
>>  *      ->acpi_ioapic_rwsem
>>  *              ->ioapic_mutex
>>  *                      ->ioapic_lock
>>  */
> 
> That looks asymetric. Why is the hotplug side not taking ioapic_mutex?
Hi Thomas,
	We decide to protect system from IOAPIC hotplug in the ACPI
layer. For ACPI enumerated IOAPICs, ioapic_mutex is redundant and
it's used to protect MPPARSE, SFI, OF enumerated IOAPICs.
Regards!
Gerry

> 
> Thanks,
> 
> 	tglx
>