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Re: [Qemu-block] coroutines: block: Co-routine re-entered recursively wh

From: Stefan Hajnoczi
Subject: Re: [Qemu-block] coroutines: block: Co-routine re-entered recursively when migrating disk with iothreads
Date: Thu, 9 Jun 2016 09:47:37 +0100

On Thu, Jun 9, 2016 at 9:25 AM, Paolo Bonzini <address@hidden> wrote:
> On 09/06/2016 09:35, Stefan Hajnoczi wrote:
>>     if (s->dataplane) {
>>         virtio_blk_data_plane_stop(s->dataplane);
>>     }
>>     virtio_save(vdev, f);
>> }
>> We reach the situation I described where BDS AioContext changes but
>> mirror_run() is still in the IOThread AioContext.
> Why is the virtio_blk_data_plane_stop necessary?  It used to sync
> between vring and virtio state, but that's not required anymore---and we
> know that the virtqueues are quiescent at this point...

I agree.  It doesn't seem necessary anymore unless I'm missing a race
condition with ioeventfd.

It was introduced so that the savevm command (without live migration!) works:

commit 10a06fd65f667a972848ebbbcac11bdba931b544
Author: Pavel Butsykin <address@hidden>
Date:   Mon Oct 26 14:42:57 2015 +0300

    virtio: sync the dataplane vring state to the virtqueue before virtio_save

We can remove it now.


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