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Re: [Qemu-devel] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handle

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler
Date: Wed, 12 Sep 2018 13:11:17 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 12/09/2018 03:31, Fam Zheng wrote:
>>> ctx is qemu_aio_context here, so there's no interaction with IOThread.
>> In this case, it should be okay to have the reentrancy, what is the bug
>> that this patch is fixing?
> The same symptom as in the previous patch: virtio_scsi_handle_cmd_vq hangs. 
> The
> reason it hangs is fixed by the previous patch, but I don't think it should be
> invoked as we're in the middle of virtio_scsi_dataplane_stop(). Applying 
> either
> one of the two patches avoids the problem, but this one is more superficial.
> What do you think?

I think it's okay if it is invoked.  The sequence is first you stop the
vq, then you drain the BlockBackends, then you switch AioContext.  All
that matters is the outcome when virtio_scsi_dataplane_stop returns.


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