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Date: Fri, 29 Aug 2014 15:59:47 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20140829145947.GA17125@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] linux-aio: avoid deadlock in nested
 aio_poll() calls
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Ming Lei <ming.lei@canonical.com>, Marcin =?utf-8?Q?Gibu=C5=82a?= <m.gibula@beyond.pl>, qemu-devel@nongnu.org


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On Mon, Aug 04, 2014 at 04:56:33PM +0100, Stefan Hajnoczi wrote:
> If two Linux AIO request completions are fetched in the same
> io_getevents() call, QEMU will deadlock if request A's callback waits
> for request B to complete using an aio_poll() loop.  This was reported
> to happen with the mirror blockjob.
>=20
> This patch moves completion processing into a BH and makes it resumable.
> Nested event loops can resume completion processing so that request B
> will complete and the deadlock will not occur.
>=20
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Ming Lei <ming.lei@canonical.com>
> Cc: Marcin Gibu=C5=82a <m.gibula@beyond.pl>
> Reported-by: Marcin Gibu=C5=82a <m.gibula@beyond.pl>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block/linux-aio.c | 71 ++++++++++++++++++++++++++++++++++++++++++-------=
------
>  1 file changed, 55 insertions(+), 16 deletions(-)

Applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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