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Re: [Qemu-block] [Qemu-devel] [PATCH 01/29] qed: Use bottom half to resu

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH 01/29] qed: Use bottom half to resume waiting requests
Date: Fri, 26 May 2017 15:40:27 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0

On 05/26/2017 03:21 PM, Kevin Wolf wrote:
> The qed driver serialises allocating write requests. When the active
> allocation is finished, the AIO callback is called, but after this, the
> next allocating request is immediately processed instead of leaving the
> coroutine. Resuming another allocation request in the same request
> coroutine means that the request now runs in the wrong coroutine.
> The following is one of the possible effects of this: The completed
> request will generally reenter its request coroutine in a bottom half,
> expecting that it completes the request in bdrv_driver_pwritev().
> However, if the second request actually yielded before leaving the
> coroutine, the reused request coroutine is in an entirely different
> place and is reentered prematurely. Not a good idea.
> Let's make sure that we exit the coroutine after completing the first
> request by resuming the next allocating request only with a bottom
> half.
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  block/qed.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)

Reviewed-by: Eric Blake <address@hidden>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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