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nbd: Avoid deadlock in client connecting to same-process server

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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 <eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20251113011625.878876-27-eblake@redhat.com>
This commit is contained in:
Eric Blake 2025-11-12 19:11:37 -06:00
parent de252f7993
commit 89179bb4d9
1 changed files with 2 additions and 2 deletions
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4
blockdev-nbd.c
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@ -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);
}
}
}