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Date: Tue, 18 Apr 2017 16:36:25 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH for-2.9-rc5 v2] block: Drain BH in
 bdrv_drained_begin
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, qemu block <qemu-block@nongnu.org>, Max Reitz <mreitz@redhat.com>

On Tue, 04/18 10:18, Paolo Bonzini wrote:
> 
> 
> On 17/04/2017 10:27, Fam Zheng wrote:
> > At this point it's even unclear to me what should be the plan for 2.9.  v1 IMO
> > was the least intrusive, but didn't cover bdrv_drain_all_begin. v2 has this
> > controversial "aio_poll(ctx_, false)",
> 
> v1 has it too:
> 
> -    bdrv_drain_recurse(bs);
> +    while (true) {
> +        if (!bdrv_drain_recurse(bs) &&
> +            !aio_poll(bdrv_get_aio_context(bs), false)) {
> +                break;
> +            }
> +    }

Yes you are right.

On the other hand, the fact that in v2 I had to add bdrv_ref/bdrv_unref around
the recursive bdrv_drain_recurse() call makes me worry a little - I assume the
same problem exists in v1 and is just latent. So maybe merging v2 is better.

> 
> I don't have any particular preference.  Both patches are self contained
> and easy to revert when the underlying root cause is fixed.
> 

Fam