From 89179bb4d91cc8d816e762c2c92f7c2120dda663 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Wed, 12 Nov 2025 19:11:37 -0600 Subject: [PATCH] nbd: Avoid deadlock in client connecting to same-process server MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit See the previous patch for a longer description of the deadlock. Now that QIONetListener supports waiting for clients in the main loop AioContext, NBD can use that to ensure that the server can make progress even when a client is intentionally starving the GMainContext from any activity not tied to an AioContext. Note that command-line arguments and QMP commands like nbd-server-start or nbd-server-stop that manipulate whether the NBD server exists are serviced in the main loop; and therefore, this patch does not fall foul of the restrictions in the previous patch about the inherent unsafe race possible if a QIONetListener can have its async callback modified by a different thread than the one servicing polls. Fixes: https://gitlab.com/qemu-project/qemu/-/issues/3169 Signed-off-by: Eric Blake Reviewed-by: Daniel P. Berrangé Message-ID: <20251113011625.878876-27-eblake@redhat.com> --- blockdev-nbd.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/blockdev-nbd.c b/blockdev-nbd.c index 1e3e634b87..696474aea9 100644 --- a/blockdev-nbd.c +++ b/blockdev-nbd.c @@ -94,10 +94,10 @@ static void nbd_update_server_watch(NBDServerData *s) { if (s->listener) { if (!s->max_connections || s->connections < s->max_connections) { - qio_net_listener_set_client_func(s->listener, nbd_accept, NULL, + qio_net_listener_set_client_aio_func(s->listener, nbd_accept, NULL, NULL); } else { - qio_net_listener_set_client_func(s->listener, NULL, NULL, NULL); + qio_net_listener_set_client_aio_func(s->listener, NULL, NULL, NULL); } } }