linux-kernel - Re: [PATCH 06/11] ACPI / gsi: Add gsi_mutex to synchronize acpi_register_gsi()/acpi_unregister

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Date:	Thu, 11 Jun 2015 21:16:24 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>,
	Jason Cooper <jason@...edaemon.net>,
	Will Deacon <Will.Deacon@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Olof Johansson <olof@...om.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [PATCH 06/11] ACPI / gsi: Add gsi_mutex to synchronize acpi_register_gsi()/acpi_unregister_gsi()

On 06/10/2015 11:58 PM, Marc Zyngier wrote:
> On 18/05/15 13:59, Hanjun Guo wrote:
>> Add a mutex for acpi_register_gsi()/acpi_unregister_gsi() to avoid
>> concurrency issues.
>>
>> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
>> ---
>>   drivers/acpi/gsi.c | 17 +++++++++++++----
>>   1 file changed, 13 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/acpi/gsi.c b/drivers/acpi/gsi.c
>> index 55b5f31..ab0dcb4 100644
>> --- a/drivers/acpi/gsi.c
>> +++ b/drivers/acpi/gsi.c
>> @@ -16,6 +16,7 @@
>>   enum acpi_irq_model_id acpi_irq_model;
>>   /* ACPI core domian pointing to GICv2/3 core domain */
>>   struct irq_domain *acpi_irq_domain __read_mostly;
>> +static DEFINE_MUTEX(gsi_mutex);
>>
>>   static unsigned int acpi_gsi_get_irq_type(int trigger, int polarity)
>>   {
>> @@ -73,20 +74,24 @@ int acpi_register_gsi(struct device *dev, u32 gsi, int trigger,
>>   	int irq;
>>   	unsigned int irq_type = acpi_gsi_get_irq_type(trigger, polarity);
>>
>> +	mutex_lock(&gsi_mutex);
>>   	irq = irq_find_mapping(acpi_irq_domain, gsi);
>>   	if (irq > 0)
>> -		return irq;
>> +		goto out;
>>
>>   	irq = irq_domain_alloc_irqs(acpi_irq_domain, 1, dev_to_node(dev),
>>   				    &gsi);
>>   	if (irq <= 0)
>> -		return -EINVAL;
>> +		goto out;
>>
>>   	/* Set irq type if specified and different than the current one */
>>   	if (irq_type != IRQ_TYPE_NONE &&
>>   		irq_type != irq_get_trigger_type(irq))
>>   		irq_set_irq_type(irq, irq_type);
>> -	return irq;
>> +
>> +out:
>> +	mutex_unlock(&gsi_mutex);
>> +	return irq > 0 ? irq : -EINVAL;
>>   }
>>   EXPORT_SYMBOL_GPL(acpi_register_gsi);
>>
>> @@ -96,8 +101,12 @@ EXPORT_SYMBOL_GPL(acpi_register_gsi);
>>    */
>>   void acpi_unregister_gsi(u32 gsi)
>>   {
>> -	int irq = irq_find_mapping(acpi_irq_domain, gsi);
>> +	int irq;
>> +
>> +	mutex_lock(&gsi_mutex);
>> +	irq = irq_find_mapping(acpi_irq_domain, gsi);
>>
>>   	irq_dispose_mapping(irq);
>> +	mutex_unlock(&gsi_mutex);
>>   }
>>   EXPORT_SYMBOL_GPL(acpi_unregister_gsi);
>>
>
> Can you point out why we need this locking? The rest of the kernel seems
> to live without it pretty well. And if we really have an issue, I'd

Hmm, I'm not so sure, I will look deep into that and come back later.

> prefer seeing it fixed in the core code rather than in something that is
> very much firmware-specific.

I agree if there are real issues.

Thanks
Hanjun
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