| Message ID | 20240205172659.476970-6-stefanha@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | virtio-blk: iothread-vq-mapping cleanups | expand |
On Mon, 05 Feb 2024 19:26, Stefan Hajnoczi <stefanha@redhat.com> wrote: >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 <hreitz@redhat.com> >Signed-off-by: Stefan Hajnoczi <stefanha@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 > > Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
On 05.02.24 18:26, Stefan Hajnoczi wrote: > 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 <hreitz@redhat.com> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > qapi/qmp-dispatch.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Stefan Hajnoczi <stefanha@redhat.com> writes: > 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 <hreitz@redhat.com> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> Feel free to merge this together with the remainder of the series.
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 { /*
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 <hreitz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- qapi/qmp-dispatch.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)