[Qemu-block] [PATCH v2] nbd/server: attach client channel to the export's AioContext

[Sergio Lopez]

On creation, the export's AioContext is set to the same one as the
BlockBackend, while the AioContext in the client QIOChannel is left
untouched.

As a result, when using data-plane, nbd_client_receive_next_request()
schedules coroutines in the IOThread AioContext, while the client's
QIOChannel is serviced from the main_loop, potentially triggering the
assertion at qio_channel_restart_[read|write].

To fix this, as soon we have the export corresponding to the client,
we call qio_channel_attach_aio_context() to attach the QIOChannel
context to the export's AioContext. This matches with the logic at
blk_aio_attached().

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1748253
Signed-off-by: Sergio Lopez <address@hidden>
---
Changelog

v2:
 - Attach the channel once after negotiation completes, avoiding
   duplication. (thanks Kevin Wolf).
---
 nbd/server.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/nbd/server.c b/nbd/server.c
index 28c3c8be85..31d624e146 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1297,6 +1297,11 @@ static coroutine_fn int nbd_negotiate(NBDClient *client, 
Error **errp)
         return ret;
     }
 
+    /* Attach the channel to the same AioContext as the export */
+    if (client->exp && client->exp->ctx) {
+        qio_channel_attach_aio_context(client->ioc, client->exp->ctx);
+    }
+
     assert(!client->optlen);
     trace_nbd_negotiate_success();
 
-- 
2.21.0