From: Lukas Straub <lukasstraub2@web.de>

Although unlikely, qemu might hang in nbd_send_request().

Allow recovery in this case by registering the yank function before
calling it.

Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Message-Id: <20210704000730.1befb596@gecko.fritz.box>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 block/nbd.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/nbd.c b/block/nbd.c
index 601fccc5bacd..f6ff1c4fb472 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -371,6 +371,9 @@ int coroutine_fn nbd_co_do_establish_connection(BlockDriverState *bs,
         return -ECONNREFUSED;
     }

+    yank_register_function(BLOCKDEV_YANK_INSTANCE(s->bs->node_name), nbd_yank,
+                           bs);
+
     ret = nbd_handle_updated_info(s->bs, NULL);
     if (ret < 0) {
         /*
@@ -381,6 +384,8 @@ int coroutine_fn nbd_co_do_establish_connection(BlockDriverState *bs,

         nbd_send_request(s->ioc, &request);

+        yank_unregister_function(BLOCKDEV_YANK_INSTANCE(s->bs->node_name),
+                                 nbd_yank, bs);
         object_unref(OBJECT(s->ioc));
         s->ioc = NULL;

@@ -390,9 +395,6 @@ int coroutine_fn nbd_co_do_establish_connection(BlockDriverState *bs,
     qio_channel_set_blocking(s->ioc, false, NULL);
     qio_channel_attach_aio_context(s->ioc, bdrv_get_aio_context(bs));

-    yank_register_function(BLOCKDEV_YANK_INSTANCE(s->bs->node_name), nbd_yank,
-                           bs);
-
     /* successfully connected */
     s->state = NBD_CLIENT_CONNECTED;
     qemu_co_queue_restart_all(&s->free_sema);
-- 
2.31.1