From effd60c878176bcaf97fa7ce2b12d04bb8ead6f7 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Thu, 18 Jan 2024 09:48:23 -0500 Subject: monitor: only run coroutine commands in qemu_aio_context monitor_qmp_dispatcher_co() runs in the iohandler AioContext that is not polled during nested event loops. The coroutine currently reschedules itself in the main loop's qemu_aio_context AioContext, which is polled during nested event loops. One known problem is that QMP device-add calls drain_call_rcu(), which temporarily drops the BQL, leading to all sorts of havoc like other vCPU threads re-entering device emulation code while another vCPU thread is waiting in device emulation code with aio_poll(). Paolo Bonzini suggested running non-coroutine QMP handlers in the iohandler AioContext. This avoids trouble with nested event loops. His original idea was to move coroutine rescheduling to monitor_qmp_dispatch(), but I resorted to moving it to qmp_dispatch() because we don't know if the QMP handler needs to run in coroutine context in monitor_qmp_dispatch(). monitor_qmp_dispatch() would have been nicer since it's associated with the monitor implementation and not as general as qmp_dispatch(), which is also used by qemu-ga. A number of qemu-iotests need updated .out files because the order of QMP events vs QMP responses has changed. Solves Issue #1933. Cc: qemu-stable@nongnu.org Fixes: 7bed89958bfbf40df9ca681cefbdca63abdde39d ("device_core: use drain_call_rcu in in qmp_device_add") Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2215192 Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2214985 Buglink: https://issues.redhat.com/browse/RHEL-17369 Signed-off-by: Stefan Hajnoczi Message-ID: <20240118144823.1497953-4-stefanha@redhat.com> Reviewed-by: Kevin Wolf Tested-by: Fiona Ebner Signed-off-by: Kevin Wolf --- monitor/qmp.c | 17 ----------------- 1 file changed, 17 deletions(-) (limited to 'monitor/qmp.c') diff --git a/monitor/qmp.c b/monitor/qmp.c index 6eee450fe4..a239945e8d 100644 --- a/monitor/qmp.c +++ b/monitor/qmp.c @@ -321,14 +321,6 @@ void coroutine_fn monitor_qmp_dispatcher_co(void *data) qemu_coroutine_yield(); } - /* - * Move the coroutine from iohandler_ctx to qemu_aio_context for - * executing the command handler so that it can make progress if it - * involves an AIO_WAIT_WHILE(). - */ - aio_co_schedule(qemu_get_aio_context(), qmp_dispatcher_co); - qemu_coroutine_yield(); - /* Process request */ if (req_obj->req) { if (trace_event_get_state(TRACE_MONITOR_QMP_CMD_IN_BAND)) { @@ -355,15 +347,6 @@ void coroutine_fn monitor_qmp_dispatcher_co(void *data) } qmp_request_free(req_obj); - - /* - * Yield and reschedule so the main loop stays responsive. - * - * Move back to iohandler_ctx so that nested event loops for - * qemu_aio_context don't start new monitor commands. - */ - aio_co_schedule(iohandler_get_aio_context(), qmp_dispatcher_co); - qemu_coroutine_yield(); } qatomic_set(&qmp_dispatcher_co, NULL); } -- cgit 1.4.1