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Date: Thu, 11 Sep 2014 15:17:56 +0800
From: Jiang Liu <jiang.liu@linux.intel.com>
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To: Thomas Gleixner <tglx@linutronix.de>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Ingo Molnar <mingo@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Yinghai Lu <yinghai@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	Grant Likely <grant.likely@linaro.org>, x86@kernel.org,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	Prarit Bhargava <prarit@redhat.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tony Luck <tony.luck@intel.com>,
	Joerg Roedel <joro@8bytes.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-acpi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	linux-pm@vger.kernel.org
Subject: Re: [Patch v4 14/16] x86, irq: Introduce helper to check whether
 an IOAPIC has been registered
References: <1409192561-19744-1-git-send-email-jiang.liu@linux.intel.com> <1409192561-19744-15-git-send-email-jiang.liu@linux.intel.com> <alpine.DEB.2.10.1409091433150.11037@nanos> <540FBB93.4020509@linux.intel.com> <alpine.DEB.2.10.1409102206300.4178@nanos>
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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
>