From: Stefan Hajnoczi <stefa...@redhat.com>
The aio_co_reschedule_self() API is designed to avoid the race
condition between scheduling the coroutine in another AioContext and
yielding.
The QMP dispatch code uses the open-coded version that appears
susceptible to the race condition at first glance:
aio_co_schedule(qemu_get_aio_context(), qemu_coroutine_self());
qemu_coroutine_yield();
The code is actually safe because the iohandler and qemu_aio_context
AioContext run under the Big QEMU Lock. Nevertheless, set a good example
and use aio_co_reschedule_self() so it's obvious that there is no race.
Suggested-by: Hanna Reitz <hre...@redhat.com>
Reviewed-by: Manos Pitsidianakis <manos.pitsidiana...@linaro.org>
Reviewed-by: Hanna Czenczek <hre...@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
Message-ID: <20240206190610.107963-6-stefa...@redhat.com>
Reviewed-by: Kevin Wolf <kw...@redhat.com>
Acked-by: Markus Armbruster <arm...@redhat.com>
Reviewed-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Kevin Wolf <kw...@redhat.com>
---
qapi/qmp-dispatch.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/qapi/qmp-dispatch.c b/qapi/qmp-dispatch.c
index 176b549473..f3488afeef 100644
--- a/qapi/qmp-dispatch.c
+++ b/qapi/qmp-dispatch.c
@@ -212,8 +212,7 @@ QDict *coroutine_mixed_fn qmp_dispatch(const QmpCommandList
*cmds, QObject *requ
* executing the command handler so that it can make progress if it
* involves an AIO_WAIT_WHILE().
*/
- aio_co_schedule(qemu_get_aio_context(), qemu_coroutine_self());
- qemu_coroutine_yield();
+ aio_co_reschedule_self(qemu_get_aio_context());
}
monitor_set_cur(qemu_coroutine_self(), cur_mon);
@@ -227,9 +226,7 @@ QDict *coroutine_mixed_fn qmp_dispatch(const QmpCommandList
*cmds, QObject *requ
* 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(),
- qemu_coroutine_self());
- qemu_coroutine_yield();
+ aio_co_reschedule_self(iohandler_get_aio_context());
}
} else {
/*
--
2.43.0
