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Re: [Qemu-block] [PATCH v3] aio: add missing aio_notify() to aio_enable_
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-block] [PATCH v3] aio: add missing aio_notify() to aio_enable_external() |
Date: |
Tue, 9 May 2017 11:06:45 -0400 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Mon, May 08, 2017 at 02:07:05PM -0400, Stefan Hajnoczi wrote:
> The main loop uses aio_disable_external()/aio_enable_external() to
> temporarily disable processing of external AioContext clients like
> device emulation.
>
> This allows monitor commands to quiesce I/O and prevent the guest from
> submitting new requests while a monitor command is in progress.
>
> The aio_enable_external() API is currently broken when an IOThread is in
> aio_poll() waiting for fd activity when the main loop re-enables
> external clients. Incrementing ctx->external_disable_cnt does not wake
> the IOThread from ppoll(2) so fd processing remains suspended and leads
> to unresponsive emulated devices.
>
> This patch adds an aio_notify() call to aio_enable_external() so the
> IOThread is kicked out of ppoll(2) and will re-arm the file descriptors.
>
> The bug can be reproduced as follows:
>
> $ qemu -M accel=kvm -m 1024 \
> -object iothread,id=iothread0 \
> -device virtio-scsi-pci,iothread=iothread0,id=virtio-scsi-pci0 \
> -drive
> if=none,id=drive0,aio=native,cache=none,format=raw,file=test.img \
> -device scsi-hd,id=scsi-hd0,drive=drive0 \
> -qmp tcp::5555,server,nowait
>
> $ scripts/qmp/qmp-shell localhost:5555
> (qemu) blockdev-snapshot-sync device=drive0 snapshot-file=sn1.qcow2
> mode=absolute-paths format=qcow2
>
> After blockdev-snapshot-sync completes the SCSI disk will be
> unresponsive. This leads to request timeouts inside the guest.
>
> Reported-by: Qianqian Zhu <address@hidden>
> Suggested-by: Fam Zheng <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> v3:
> * s/dec_fetch/fetch_dec/ [Fam]
> ---
> include/block/aio.h | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block
Stefan
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