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Date: Wed, 20 Oct 2010 08:16:50 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH 2/3] Make paio subsystem use threadlets
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Arun R Bharadwaj <arun@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On 10/20/2010 04:30 AM, Stefan Hajnoczi wrote:
>
>>      } else if (acb->ret == -EINPROGRESS) {
>>          active = 1;
>>      }
>> -    mutex_unlock(&lock);
>>
>>      if (active) {
>>          /* fail safe: if the aio could not be canceled, we wait for
>>      
> while (qemu_paio_error(acb) == EINPROGRESS)
>      ;
>
> Tight loop with no memory barrier reading a memory location that is
> updated by another thread.  We shouldn't communicate between threads
> without barriers.
>    

We shouldn't use a tight loop period.  A condition should be used if 
signalling is needed.

And we shouldn't rely on atomic assignments to communicate between 
threads.  Just use a mutex and avoid being fancier than we need to be.

Regards,

Anthony Liguori

> Stefan
>
>