Re: [Qemu-block] [PATCH v4] throttle-groups: drain before detaching ThrottleState

[Stefan Hajnoczi]

On Fri, Nov 10, 2017 at 03:19:34PM +0000, 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>
> ---
> v4:
>  * Simplified patch in response to Berto's review
> ---
>  block/block-backend.c   | 2 ++
>  block/throttle-groups.c | 6 ++++++
>  2 files changed, 8 insertions(+)

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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