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

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Date:	Tue, 16 Aug 2016 11:41:47 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	"Zheng, Lv" <lv.zheng@...el.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Tomasz Nowicki <tn@...ihalf.com>
Cc:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"helgaas@...nel.org" <helgaas@...nel.org>,
	"rafael@...nel.org" <rafael@...nel.org>,
	"will.deacon@....com" <will.deacon@....com>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"shijie.huang@....com" <shijie.huang@....com>,
	"robert.richter@...iumnetworks.com" 
	<robert.richter@...iumnetworks.com>,
	"mw@...ihalf.com" <mw@...ihalf.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"andrea.gallo@...aro.org" <andrea.gallo@...aro.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"al.stone@...aro.org" <al.stone@...aro.org>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	"ddaney.cavm@...il.com" <ddaney.cavm@...il.com>,
	"okaya@...eaurora.org" <okaya@...eaurora.org>
Subject: Re: [PATCH V8 2/8] ACPI: Add new IORT functions to support MSI domain
 handling

On 16/08/16 03:15, Zheng, Lv wrote:
> Hi,
> 
>> From: linux-acpi-owner@...r.kernel.org [mailto:linux-acpi-owner@...r.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...