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Re: [Qemu-block] [Qemu-devel] [PATCH 2/3] block: use BDRV_POLL_WHILE() i

From: Kevin Wolf
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH 2/3] block: use BDRV_POLL_WHILE() in bdrv_rw_vmstate()
Date: Thu, 18 May 2017 09:57:59 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 17.05.2017 um 22:16 hat Eric Blake geschrieben:
> On 05/17/2017 12:09 PM, Stefan Hajnoczi wrote:
> > Calling aio_poll() directly may have been fine previously, but this is
> > the future, man!
> lol
> >  The difference between an aio_poll() loop and
> > BDRV_POLL_WHILE() is that BDRV_POLL_WHILE() releases the AioContext
> > around aio_poll().
> > 
> > This allows the IOThread to run fd handlers or BHs to complete the
> > request.  Failure to release the AioContext causes deadlocks.
> > 
> > Using BDRV_POLL_WHILE() partially fixes a 'savevm' hang with -object
> > iothread.
> I'm surprised at how many separate hangs we actually had!

How hard would it be to write some test cases for this? Dataplane has
a serious lack of automated testing.


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