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Date: Wed, 10 Sep 2014 22:08:00 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Jiang Liu <jiang.liu@linux.intel.com>
cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
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Subject: Re: [Patch v4 14/16] x86, irq: Introduce helper to check whether an
 IOAPIC has been registered
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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?

Thanks,

	tglx