From: Kevin Wolf <kwolf@redhat.com>
To: Eric Blake <eblake@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>,
qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>,
Fam Zheng <famz@redhat.com>,
qemu-block@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 2/3] block: use BDRV_POLL_WHILE() in bdrv_rw_vmstate()
Date: Thu, 18 May 2017 09:57:59 +0200 [thread overview]
Message-ID: <20170518075759.GA4646@noname.redhat.com> (raw)
In-Reply-To: <e6d9417e-87bb-a88f-4f55-0a72aae0a212@redhat.com>
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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.
Kevin
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next prev parent reply other threads:[~2017-05-18 7:58 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-17 17:09 [Qemu-devel] [PATCH 0/3] block: fix 'savevm' hang with -object iothread Stefan Hajnoczi
2017-05-17 17:09 ` [Qemu-devel] [PATCH 1/3] block: count bdrv_co_rw_vmstate() requests Stefan Hajnoczi
2017-05-17 20:09 ` Eric Blake
2017-05-17 17:09 ` [Qemu-devel] [PATCH 2/3] block: use BDRV_POLL_WHILE() in bdrv_rw_vmstate() Stefan Hajnoczi
2017-05-17 20:16 ` Eric Blake
2017-05-17 20:47 ` Paolo Bonzini
2017-05-18 7:57 ` Kevin Wolf [this message]
2017-05-18 8:06 ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
2017-05-18 8:22 ` Kevin Wolf
2017-05-18 8:05 ` Stefan Hajnoczi
2017-05-17 17:09 ` [Qemu-devel] [PATCH 3/3] migration: avoid recursive AioContext locking in save_vmstate() Stefan Hajnoczi
2017-05-17 20:24 ` Eric Blake
2017-05-18 8:18 ` Kevin Wolf
2017-05-19 9:07 ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
2017-05-17 20:49 ` [Qemu-devel] [PATCH 0/3] block: fix 'savevm' hang with -object iothread Paolo Bonzini
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