When starting a dummy QEMU process with virsh version, monitor_init_qmp()
enables IOThread monitoring of the QMP fd by default. However, a race
condition exists during the initialization phase: the IOThread only removes
the main thread's fd watch when it reaches qio_net_listener_set_client_func_full(),
which may be delayed under high system load.
This creates a window between monitor_qmp_setup_handlers_bh() and
qio_net_listener_set_client_func_full() where both the main thread and
IOThread are simultaneously monitoring the same fd and processing events.
This race can cause either the main thread or the IOThread to hang and
become unresponsive.
Fix this by proactively cleaning up the listener's IO sources in
monitor_init_qmp() before the IOThread initializes QMP monitoring,
ensuring exclusive fd ownership and eliminating the race condition.
Signed-off-by: Jie Song <songjie_yewu@cmss.chinamobile.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20251125140706.114197-1-mail@jiesong.me>
(cherry picked from commit e714f1a3d4d1e66b9a3ff4be1ff999c32bbef29e)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
d6b9de8f9e