[PATCH 2/3] block/nbd: on shutdown terminate connection attempt

[Vladimir Sementsov-Ogievskiy]

On shutdown nbd driver may be in a connecting state. We should shutdown
it as well, otherwise we may hang in
nbd_teardown_connection, waiting for conneciton_co to finish in
BDRV_POLL_WHILE(bs, s->connection_co) loop if remote server is down.

How to reproduce the dead lock:

1. Create nbd-fault-injector.conf with the following contents:

[inject-error "mega1"]
event=data
io=readwrite
when=before

2. In one terminal run nbd-fault-injector in a loop, like this:

n=1; while true; do
    echo $n; ((n++));
    ./nbd-fault-injector.py 127.0.0.1:10000 nbd-fault-injector.conf;
done

3. In another terminal run qemu-io in a loop, like this:

n=1; while true; do
    echo $n; ((n++));
    ./qemu-io -c 'read 0 512' nbd+tcp://127.0.0.1:10000;
done

After some time, qemu-io will hang. Note, that this hang may be
triggered by another bug, so the whole case is fixed only together with
commit "block/nbd: allow drain during reconnect attempt".

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/nbd.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/block/nbd.c b/block/nbd.c
index 49254f1c3c..42146a26f7 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -206,11 +206,15 @@ static void nbd_teardown_connection(BlockDriverState *bs)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
-    if (s->state == NBD_CLIENT_CONNECTED) {
+    if (s->ioc) {
         /* finish any pending coroutines */
-        assert(s->ioc);
         qio_channel_shutdown(s->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
+    } else if (s->sioc) {
+        /* abort negotiation */
+        qio_channel_shutdown(QIO_CHANNEL(s->sioc), QIO_CHANNEL_SHUTDOWN_BOTH,
+                             NULL);
     }
+
     s->state = NBD_CLIENT_QUIT;
     if (s->connection_co) {
         if (s->connection_co_sleep_ns_state) {
@@ -1452,6 +1456,8 @@ static int nbd_client_connect(BlockDriverState *bs, Error 
**errp)
         return -ECONNREFUSED;
     }
 
+    s->sioc = sioc;
+
     /* NBD handshake */
     trace_nbd_client_connect(s->export);
     qio_channel_set_blocking(QIO_CHANNEL(sioc), false, NULL);
@@ -1468,6 +1474,7 @@ static int nbd_client_connect(BlockDriverState *bs, Error 
**errp)
     g_free(s->info.name);
     if (ret < 0) {
         object_unref(OBJECT(sioc));
+        s->sioc = NULL;
         return ret;
     }
     if (s->x_dirty_bitmap && !s->info.base_allocation) {
@@ -1493,8 +1500,6 @@ static int nbd_client_connect(BlockDriverState *bs, Error 
**errp)
         }
     }
 
-    s->sioc = sioc;
-
     if (!s->ioc) {
         s->ioc = QIO_CHANNEL(sioc);
         object_ref(OBJECT(s->ioc));
@@ -1515,6 +1520,7 @@ static int nbd_client_connect(BlockDriverState *bs, Error 
**errp)
         nbd_send_request(s->ioc ?: QIO_CHANNEL(sioc), &request);
 
         object_unref(OBJECT(sioc));
+        s->sioc = NULL;
 
         return ret;
     }
-- 
2.21.0