linux-kernel - Re: [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifier interface

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Message-ID: <4A3AC3F6.8070402@novell.com>
Date:	Thu, 18 Jun 2009 18:47:18 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Davide Libenzi <davidel@...ilserver.org>
CC:	"Michael S. Tsirkin" <mst@...hat.com>, kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	avi@...hat.com, paulmck@...ux.vnet.ibm.com,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifier
 interface

Davide Libenzi wrote:
> On Thu, 18 Jun 2009, Gregory Haskins wrote:
>
>   
>> Davide Libenzi wrote:
>>     
>>> On Thu, 18 Jun 2009, Gregory Haskins wrote:
>>>
>>>   
>>>       
>>>> Actually there is only one (the tx-thread) aside from the eventfd
>>>> imposed workqueue one.  Incidentally, I would love to get rid of the
>>>> other thread too, so I am not just picking on eventfd ;).  The other is
>>>> a lot harder since it has to update the virtio-ring and may need to page
>>>> in guest memory to do so.
>>>>     
>>>>         
>>> No, there is the interface rx softirq too, that makes two.
>>>       
>> Actually, I believe you are mistaken.  It normally executes the softirq
>> in interrupt context, not a thread.
>>
>> But I digress.  Lets just shelve the SRCU conversation for another day. 
>> It was my bad for introducing it now prematurely to solve a mostly
>> unrelated problem: the module-reference thing.  I didn't realize the
>> SRCU change would be so controversial, and I didn't think to split
>> things apart as I have done today.
>>
>> But the fact is: I do not see any way to actually use your referenceless
>> POLLHUP release code in a race free way without doing something like I
>> propose in 3/4, 4/4.   Lets keep the discussion focused on that for now,
>> if we could.
>>     
>
> OK, since I got literally swamped by the amount of talks and patches over 
> this theoretically simple topic, would you mind  1) posting the global 
> patch over eventfd  2) describe exactly what races are you talking about 
> 3) explain why this should be any concern of eventfd at all?
>
>
>   
Yes, I can do that.  Thanks Davide,

-Greg



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