From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@linaro.org>
Subject: Re: [PATCH v4 18/18] xen/arm: IRQ: Handle multiple
	action per IRQ
Date: Wed, 23 Apr 2014 15:56:09 +0100
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To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: xen-devel@lists.xenproject.org, Keir Fraser <keir@xen.org>, tim@xen.org, Jan Beulich <jbeulich@suse.com>, stefano.stabellini@citrix.com
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On 04/23/2014 03:07 PM, Ian Campbell wrote:
> On Tue, 2014-04-22 at 13:58 +0100, Julien Grall wrote:
>> On ARM, it may happen (eg ARM SMMU) to setup multiple handler for the same
>> interrupt.
>>
>> To be able to use multiple action, the driver has to explicitly call
>> {setup,request}_irq with IRQF_SHARED as 2nd parameter.
>>
>> The behavior stays the same on x86, e.g only one action is handled.
>>
>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
>> Cc: Keir Fraser <keir@xen.org>
>> Cc: Jan Beulich <jbeulich@suse.com>
>>
>> ---
>>     Changes in v4:
>>         - Go back to a single custom linked list. The double linked-list
>>         doesn't fit the requirements (i.e browsing safely without look) and
>>         the llist.h from Linux doesn't allow use to delete a node in the middle
>>         of the list.
> 
> Is this variant any safer?

Yes, everything is protected by a desc->lock, except in do_IRQ (see
below why).

>> +        do
>> +        {
>> +            action->handler(irq, action->dev_id, regs);
>> +            action = action->next;
>> +        } while ( action );
> 
> What happens if action is freed and recycled in the midst of this loop?

Nothing, the action won't be free until IRQ_INPROGRESS is set (see do ..
while at the end of release_irq).

Regards,

-- 
Julien Grall