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Re: [Xen-devel] [PATCH] x86/IRQ: fix create_irq() after c/s 24068:692817

To: "Keir Fraser" <keir@xxxxxxx>
Subject: Re: [Xen-devel] [PATCH] x86/IRQ: fix create_irq() after c/s 24068:6928172f7ded
From: "Jan Beulich" <JBeulich@xxxxxxxx>
Date: Fri, 04 Nov 2011 15:05:16 +0000
Cc: andrew.cooper3@xxxxxxxxxx, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Haitao Shan <haitao.shan@xxxxxxxxx>, xiantao.zhang@xxxxxxxxx
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>>> On 04.11.11 at 15:41, Keir Fraser <keir@xxxxxxx> wrote:
> On 04/11/2011 11:52, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> 
>> init_one_irq_desc() must be called with interrupts enabled (as it may
>> call functions from the xmalloc() group). Rather than mis-using
>> vector_lock to also protect the finding of an unused IRQ, make this
>> lockless through using cmpxchg(), and obtain the lock only around the
>> actual assignment of the vector.
> 
> Looks fine to me.
> 
> Acked-by: Keir Fraser <keir@xxxxxxx>
> 
>> Also fold find_unassigned_irq() into its only caller.
>> 
>> It is, btw, questionable whether create_irq() calling
>> __assign_irq_vector() (rather than assign_irq_vector()) is actually
>> correct - desc->affinity appears to not get initialized properly in
>> this case.

Any thought on this one? Adjusting this would have the nice side
effect of the function no longer explicitly acquiring vector_lock.

Jan


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