mirror: Hold main AioContext lock for calling bdrv_open_backing_file()

bdrv_open_backing_file() calls bdrv_open_inherit(), so all callers must
hold the main AioContext lock.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230525124713.401149-6-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -3478,6 +3478,8 @@ int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
  * itself, all options starting with "${bdref_key}." are considered part of the
  * BlockdevRef.
  *
+ * The caller must hold the main AioContext lock.
+ *
  * TODO Can this be unified with bdrv_open_image()?
  */
 int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,

block/mirror.c

@@ -662,11 +662,15 @@ static int mirror_exit_common(Job *job)
     bool abort = job->ret < 0;
     int ret = 0;
 
+    GLOBAL_STATE_CODE();
+
     if (s->prepared) {
         return 0;
     }
     s->prepared = true;
 
+    aio_context_acquire(qemu_get_aio_context());
+
     mirror_top_bs = s->mirror_top_bs;
     bs_opaque = mirror_top_bs->opaque;
     src = mirror_top_bs->backing->bs;
@@ -789,6 +793,8 @@ static int mirror_exit_common(Job *job)
     bdrv_unref(mirror_top_bs);
     bdrv_unref(src);
 
+    aio_context_release(qemu_get_aio_context());
+
     return ret;
 }