The fact that the bs->aio_context is changing can confuse the dataplane
iothread, because of the now fine granularity aio context lock.
bdrv_drain should rather be a bdrv_drained_begin/end pair, but since
bs->aio_context is changing, we can just use aio_disable_external and
bdrv_parent_drained_begin.

Reported-by: Ed Swierk <eswierk@skyportsystems.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index b8a3011..a995a8e 100644
--- a/block.c
+++ b/block.c
@@ -4396,11 +4396,12 @@ void bdrv_attach_aio_context(BlockDriverState *bs,
 
 void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
 {
-    AioContext *ctx;
+    AioContext *ctx = bdrv_get_aio_context(bs);
 
+    aio_disable_external(ctx);
+    bdrv_parent_drained_begin(bs);
     bdrv_drain(bs); /* ensure there are no in-flight requests */
 
-    ctx = bdrv_get_aio_context(bs);
     while (aio_poll(ctx, false)) {
         /* wait for all bottom halves to execute */
     }
@@ -4412,6 +4413,8 @@ void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
      */
     aio_context_acquire(new_context);
     bdrv_attach_aio_context(bs, new_context);
+    bdrv_parent_drained_end(bs);
+    aio_enable_external(ctx);
     aio_context_release(new_context);
 }
 
-- 
2.9.3

Am 10.04.2017 um 17:05 hat Fam Zheng geschrieben:
> The fact that the bs->aio_context is changing can confuse the dataplane
> iothread, because of the now fine granularity aio context lock.
> bdrv_drain should rather be a bdrv_drained_begin/end pair, but since
> bs->aio_context is changing, we can just use aio_disable_external and
> bdrv_parent_drained_begin.
> 
> Reported-by: Ed Swierk <eswierk@skyportsystems.com>
> Signed-off-by: Fam Zheng <famz@redhat.com>

Reviewed-by: Kevin Wolf <kwolf@redhat.com>

On Mon, Apr 10, 2017 at 11:05:34PM +0800, Fam Zheng wrote:
> The fact that the bs->aio_context is changing can confuse the dataplane
> iothread, because of the now fine granularity aio context lock.
> bdrv_drain should rather be a bdrv_drained_begin/end pair, but since
> bs->aio_context is changing, we can just use aio_disable_external and
> bdrv_parent_drained_begin.
> 
> Reported-by: Ed Swierk <eswierk@skyportsystems.com>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>