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Re: [Qemu-devel] [PATCH v3 4/4] migration: use bdrv_drain_all_begin/end(
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v3 4/4] migration: use bdrv_drain_all_begin/end() instead bdrv_drain_all() |
Date: |
Mon, 22 May 2017 12:40:10 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 |
On 05/22/2017 08:57 AM, Stefan Hajnoczi wrote:
> blk/bdrv_drain_all() only takes effect for a single instant and then
> resumes block jobs, guest devices, and other external clients like the
> NBD server. This can be handy when performing a synchronous drain
> before terminating the program, for example.
>
> Monitor commands usually need to quiesce I/O across an entire code
> region so blk/bdrv_drain_all() is not suitable. They must use
> bdrv_drain_all_begin/end() to mark the region. This prevents new I/O
> requests from slipping in or worse - block jobs completing and modifying
> the graph.
>
> I audited other blk/bdrv_drain_all() callers but did not find anything
> that needs a similar fix. This patch fixes the savevm/loadvm commands.
> Although I haven't encountered a read world issue this makes the code
> safer.
>
> Suggested-by: Kevin Wolf <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> migration/savevm.c | 18 +++++++++++++++---
> 1 file changed, 15 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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- [Qemu-devel] [PATCH v3 0/4] block: fix 'savevm' hang with -object iothread, Stefan Hajnoczi, 2017/05/22
- [Qemu-devel] [PATCH v3 2/4] block: use BDRV_POLL_WHILE() in bdrv_rw_vmstate(), Stefan Hajnoczi, 2017/05/22
- [Qemu-devel] [PATCH v3 1/4] block: count bdrv_co_rw_vmstate() requests, Stefan Hajnoczi, 2017/05/22
- [Qemu-devel] [PATCH v3 3/4] migration: avoid recursive AioContext locking in save_vmstate(), Stefan Hajnoczi, 2017/05/22
- [Qemu-devel] [PATCH v3 4/4] migration: use bdrv_drain_all_begin/end() instead bdrv_drain_all(), Stefan Hajnoczi, 2017/05/22
- Re: [Qemu-devel] [PATCH v3 4/4] migration: use bdrv_drain_all_begin/end() instead bdrv_drain_all(),
Eric Blake <=
- Re: [Qemu-devel] [Qemu-block] [PATCH v3 0/4] block: fix 'savevm' hang with -object iothread, Stefan Hajnoczi, 2017/05/30