Re: [PATCH V8 2/8] ACPI: Add new IORT functions to support MSI domain handling

[Marc Zyngier <marc.zyngier@arm.com>]

On 16/08/16 03:15, Zheng, Lv wrote:
> Hi,
> 
>> From: linux-acpi-owner@vger.kernel.org [mailto:linux-acpi-owner@vger.kernel.org] On Behalf Of Lorenzo
>> Pieralisi
>> Subject: Re: [PATCH V8 2/8] ACPI: Add new IORT functions to support MSI domain handling
>>
>> On Thu, Aug 11, 2016 at 12:06:32PM +0200, Tomasz Nowicki wrote:
>>
>> [...]
>>
>>> +/**
>>> + * iort_register_domain_token() - register domain token and related ITS ID
>>> + * to the list from where we can get it back later on.
>>> + * @trans_id: ITS ID.
>>> + * @fw_node: Domain token.
>>> + *
>>> + * Returns: 0 on success, -ENOMEM if no memory when allocating list element
>>> + */
>>> +int iort_register_domain_token(int trans_id, struct fwnode_handle *fw_node)
>>> +{
>>> +	struct iort_its_msi_chip *its_msi_chip;
>>> +
>>> +	its_msi_chip = kzalloc(sizeof(*its_msi_chip), GFP_KERNEL);
>>
>> I spotted this while reworking my ARM SMMU series, this may sleep
>> and that's no good given that we call it within the acpi_probe_lock.
>>
>> Same goes for irq_domain_alloc_fwnode() (that we call in
>> gic_v2_acpi_init()), we have got to fix this usage, I will see with
>> Marc what's the best way to do it.
> 
> If we can ensure that all table device probe entries are created
> during link stage or early stage. I think you can safely unlock probe
> lock before invoking acpi_table_parse() in
> __acpi_probe_device_table().

That'd be quite risky, as this lock is the only thing that protects the
acpi_probe_entry pointer (I really wish the ACPI API was less global
variable happy), and I don't see how we can guarantee to only ever
execute this in a single-threaded environment.

An alternative would be to turn the spinlock into a mutex, which will
allow sleeping, and yet provide the required mutual exclusion.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...