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Date: Mon, 20 Aug 2012 09:22:52 +0200
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Subject: Re: [Qemu-devel] [PATCH RFT 0/3] iscsi: fix NULL dereferences /
 races between task completion and abort
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To: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
Cc: qemu-devel@nongnu.org, ronniesahlberg@gmail.com

Il 19/08/2012 21:22, Stefan Priebe - Profihost AG ha scritto:
> 
>> No problem, my fault---I'm just back and I haven't really started again
>> all my stuff, so the patch was not tested.
>>
>> This should fix it, though.
> 
> Booting works fine now. But the VM starts to hang after trying to unmap
> large regions. No segfault or so just not reacting anymore.

This is expected; unfortunately cancellation right now is a synchronous
operation in the block layer.  SCSI is the first big user of
cancellation, and it would indeed benefit from asynchronous cancellation.

Without these three patches, you risk corruption in case the following
happens:

    qemu                 target
  -----------------------------------
    send unmap -------->
    cancel unmap ------>
    send write -------->
       <---------------- complete write
                         <unmap just written sector>
       <---------------- complete unmap
       <---------------- cancellation done (unmap complete)

Paolo