[Qemu-devel] [PATCH] mirror: Quiesce source during "mirror_exit"

[Qemu-devel] [PATCH] mirror: Quiesce source during "mirror_exit"

[Fam Zheng]

With dataplane, the ioeventfd events could be dispatched after
mirror_run releases the dirty bitmap, but before mirror_exit actually
does the device switch, because the iothread will still be running, and
it will cause silent data loss.

Fix this by adding a bdrv_drained_begin/end pair around the window, so
that no new external request will be handled.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/mirror.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/mirror.c b/block/mirror.c
index 52c9abf..0e8f556 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -388,6 +388,7 @@ static void mirror_exit(BlockJob *job, void *opaque)
     bdrv_unref(s->target);
     block_job_completed(&s->common, data->ret);
     g_free(data);
+    bdrv_drained_end(src);
     bdrv_unref(src);
 }
 
@@ -607,6 +608,9 @@ immediate_exit:
 
     data = g_malloc(sizeof(*data));
     data->ret = ret;
+    /* Before we switch to target in mirror_exit, make sure data doesn't
+     * change. */
+    bdrv_drained_begin(s->common.bs);
     block_job_defer_to_main_loop(&s->common, mirror_exit, data);
 }
 
-- 
2.4.3

Re: [Qemu-devel] [PATCH] mirror: Quiesce source during "mirror_exit"

[Jeff Cody]

On Mon, Nov 23, 2015 at 10:28:04AM +0800, Fam Zheng wrote:
> With dataplane, the ioeventfd events could be dispatched after
> mirror_run releases the dirty bitmap, but before mirror_exit actually
> does the device switch, because the iothread will still be running, and
> it will cause silent data loss.
> 
> Fix this by adding a bdrv_drained_begin/end pair around the window, so
> that no new external request will be handled.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block/mirror.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 52c9abf..0e8f556 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -388,6 +388,7 @@ static void mirror_exit(BlockJob *job, void *opaque)
>      bdrv_unref(s->target);
>      block_job_completed(&s->common, data->ret);
>      g_free(data);
> +    bdrv_drained_end(src);
>      bdrv_unref(src);
>  }
>  
> @@ -607,6 +608,9 @@ immediate_exit:
>  
>      data = g_malloc(sizeof(*data));
>      data->ret = ret;
> +    /* Before we switch to target in mirror_exit, make sure data doesn't
> +     * change. */
> +    bdrv_drained_begin(s->common.bs);
>      block_job_defer_to_main_loop(&s->common, mirror_exit, data);
>  }
>  
> -- 
> 2.4.3
>
Thanks, applied to my block branch:

git://github.com/codyprime/qemu-kvm-jtc.git block