[v1] Miscellaneous changes for 2025-10-28

[PULL 06/18] qobject: make refcount atomic

Paolo Bonzini posted 18 patches 2 weeks, 3 days ago

Diff against v2
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Maintainers: Magnus Kulke <magnus.kulke@linux.microsoft.com>, Wei Liu <wei.liu@kernel.org>, "Gonglei (Arei)" <arei.gonglei@huawei.com>, Zhenwei Pi <pizhenwei@bytedance.com>, "Michael S. Tsirkin" <mst@redhat.com>, Stefano Garzarella <sgarzare@redhat.com>, Laurent Vivier <lvivier@redhat.com>, Amit Shah <amit@kernel.org>, Stefan Berger <stefanb@linux.vnet.ibm.com>, "Marc-André Lureau" <marcandre.lureau@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, "Alex Bennée" <alex.bennee@linaro.org>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Peter Maydell <peter.maydell@linaro.org>, Igor Mitsyanko <i.mitsyanko@gmail.com>, "Clément Chigot" <chigot@adacore.com>, Frederic Konrad <konrad.frederic@yahoo.fr>, Alberto Garcia <berto@igalia.com>, Thomas Huth <huth@tuxfamily.org>, Halil Pasic <pasic@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, Jason Herne <jjherne@linux.ibm.com>, Yoshinori Sato <yoshinori.sato@nifty.com>, Magnus Damm <magnus.damm@gmail.com>, Nicholas Piggin <npiggin@gmail.com>, Harsh Prateek Bora <harshpb@linux.ibm.com>, "Collin L. Walling" <walling@linux.ibm.com>, Stefano Stabellini <sstabellini@kernel.org>, Anthony PERARD <anthony@xenproject.org>, Paul Durrant <paul@xen.org>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Alistair Francis <alistair@alistair23.me>, "Daniel P. Berrangé" <berrange@redhat.com>, Eduardo Habkost <eduardo@habkost.net>, Richard Henderson <richard.henderson@linaro.org>, Helge Deller <deller@gmx.de>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Corey Minyard <minyard@acm.org>, Paul Burton <paulburton@kernel.org>, Aleksandar Rikalo <arikalo@gmail.com>, Aurelien Jarno <aurelien@aurel32.net>, Palmer Dabbelt <palmer@dabbelt.com>, Weiwei Li <liwei1518@gmail.com>, Daniel Henrique Barboza <dbarboza@ventanamicro.com>, Liu Zhiwei <zhiwei_liu@linux.alibaba.com>, Fam Zheng <fam@euphon.net>, Samuel Thibault <samuel.thibault@ens-lyon.org>, Michael Rolnik <mrolnik@gmail.com>, Antony Pavlov <antonynpavlov@gmail.com>, Joel Stanley <joel@jms.id.au>, Vijai Kumar K <vijai@behindbytes.com>, Samuel Tardieu <sam@rfc1149.net>, Gustavo Romero <gustavo.romero@linaro.org>, Raphael Norwitz <raphael@enfabrica.net>, Stefan Hajnoczi <stefanha@redhat.com>, Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>, Dmitry Osipenko <dmitry.osipenko@collabora.com>, Markus Armbruster <armbru@redhat.com>, Fabiano Rosas <farosas@suse.de>, "Dr. David Alan Gilbert" <dave@treblig.org>, Zhang Chen <zhangckid@gmail.com>, Li Zhijian <lizhijian@fujitsu.com>, Jason Wang <jasowang@redhat.com>, Manos Pitsidianakis <manos.pitsidianakis@linaro.org>, John Snow <jsnow@redhat.com>, Cleber Rosa <crosa@redhat.com>, Cameron Esfahani <dirty@apple.com>, Roman Bolshakov <rbolshakov@ddn.com>, Phil Dennis-Jordan <phil@philjordan.eu>, Marcelo Tosatti <mtosatti@redhat.com>, Reinoud Zandijk <reinoud@netbsd.org>, Sunil Muthuswamy <sunilmut@microsoft.com>, Max Filippov <jcmvbkbc@gmail.com>, Lukas Straub <lukasstraub2@web.de>

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[PULL 06/18] qobject: make refcount atomic

Posted by Paolo Bonzini 2 weeks, 3 days ago

The Rust bindings for QObject will only operate on complete objects,
treating them as immutable as long as the Rust QObject is live.

With that constraint, it is trivial for Rust code to treat QObjects as
thread-safe; all that's needed is to make reference count operations
atomic.  Do the same when the C code adds or removes references, since
we don't really know what the Rust code is up to; of course C code will
have to agree with not making changes to the QObjects after they've
been passed to Rust code.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 include/qobject/qobject.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/qobject/qobject.h b/include/qobject/qobject.h
index a6244d0ce00..02f4c6a6eb2 100644
--- a/include/qobject/qobject.h
+++ b/include/qobject/qobject.h
@@ -32,6 +32,7 @@
 #ifndef QOBJECT_H
 #define QOBJECT_H
 
+#include "qemu/atomic.h"
 #include "qapi/qapi-builtin-types.h"
 
 /* Not for use outside include/qobject/ */
@@ -73,7 +74,7 @@ QEMU_BUILD_BUG_MSG(QTYPE__MAX != 7,
 static inline void qobject_ref_impl(QObject *obj)
 {
     if (obj) {
-        obj->base.refcnt++;
+        qatomic_inc(&obj->base.refcnt);
     }
 }
 
@@ -95,7 +96,7 @@ void qobject_destroy(QObject *obj);
 static inline void qobject_unref_impl(QObject *obj)
 {
     assert(!obj || obj->base.refcnt);
-    if (obj && --obj->base.refcnt == 0) {
+    if (obj && qatomic_fetch_dec(&obj->base.refcnt) == 1) {
         qobject_destroy(obj);
     }
 }
-- 
2.51.1