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Re: [Qemu-devel] [PATCH v4] throttle-groups: drain before detaching Thro

From: Alberto Garcia
Subject: Re: [Qemu-devel] [PATCH v4] throttle-groups: drain before detaching ThrottleState
Date: Mon, 13 Nov 2017 11:00:10 +0100
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Fri 10 Nov 2017 04:19:34 PM CET, Stefan Hajnoczi wrote:
> I/O requests hang after stop/cont commands at least since QEMU 2.10.0
> with -drive iops=100:
>   (guest)$ dd if=/dev/zero of=/dev/vdb oflag=direct count=1000
>   (qemu) stop
>   (qemu) cont
>   ...I/O is stuck...
> This happens because blk_set_aio_context() detaches the ThrottleState
> while requests may still be in flight:
>   if (tgm->throttle_state) {
>       throttle_group_detach_aio_context(tgm);
>       throttle_group_attach_aio_context(tgm, new_context);
>   }
> This patch encloses the detach/attach calls in a drained region so no
> I/O request is left hanging.  Also add assertions so we don't make the
> same mistake again in the future.
> Reported-by: Yongxue Hong <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>

Reviewed-by: Alberto Garcia <address@hidden>


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