Not sure if this is correct, but at least it makes qemu-iotests 127 pass
again.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/io.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/block/io.c b/block/io.c
index 832d2536bf..d3dde4d7fd 100644
--- a/block/io.c
+++ b/block/io.c
@@ -309,6 +309,10 @@ static void bdrv_co_drain_bh_cb(void *opaque)
     BdrvCoDrainData *data = opaque;
     Coroutine *co = data->co;
     BlockDriverState *bs = data->bs;
+    AioContext *ctx;
+
+    ctx = bdrv_get_aio_context(bs);
+    aio_context_acquire(ctx);
 
     if (bs) {
         bdrv_dec_in_flight(bs);
@@ -324,6 +328,8 @@ static void bdrv_co_drain_bh_cb(void *opaque)
         bdrv_drain_all_begin();
     }
 
+    aio_context_release(ctx);
+
     data->done = true;
     aio_co_wake(co);
 }
-- 
2.13.6