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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Tue, 18 Apr 2017 10:18:25 +0200
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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: Fam Zheng <famz@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu block <qemu-block@nongnu.org>, qemu-devel <qemu-devel@nongnu.org>, Max Reitz <mreitz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>



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;
+            }
+    }

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

Thanks,

Paolo

> however its alternative,
> "aio_poll(qemu_get_aio_context(), false)", "introduces" another crash that is
> not seen otherwise.
> 
> What should we do now?