SUMMARY This bug has been annoying me for quite a while. Sometimes, if you close an application, kwin will freeze and then unfreeze itself shortly after. I have not found a reliable way to reproduce this freeze. STEPS TO REPRODUCE 1. Close Firefox OBSERVED RESULT There's a 50/50 chance that kwin will freeze for some amount of time. * thread #1, name = 'kwin_wayland', stop reason = signal SIGSTOP * frame #0: 0x00007f9fddf18644 libQt5Core.so.5`std::atomic<QObjectPrivate::Connection*>::load(this=0x0000560d8c692770, __m=memory_order_relaxed) const at atomic:523:32 frame #1: 0x00007f9fddf16329 libQt5Core.so.5`QObjectPrivate::Connection* QAtomicOps<QObjectPrivate::Connection*>::loadRelaxed<QObjectPrivate::Connection*>(_q_value=0x0000560d8c692770) at qatomic_cxx11.h:239:29 frame #2: 0x00007f9fddf12efc libQt5Core.so.5`QBasicAtomicPointer<QObjectPrivate::Connection>::loadRelaxed(this=0x0000560d8c692770) const at qbasicatomic.h:248:64 frame #3: 0x00007f9fddf063cd libQt5Core.so.5`QObjectPrivate::ConnectionData::removeConnection(this=0x0000560d8bcf1010, c=0x0000560d8d241320) at qobject.cpp:398:103 frame #4: 0x00007f9fddf0774d libQt5Core.so.5`QObject::~QObject(this=0x0000560d8c1dbeb0) at qobject.cpp:1062:41 frame #5: 0x00007f9fdfa71630 libKWaylandServer.so.5`KWaylandServer::SurfaceInterface::~SurfaceInterface(this=0x0000560d8c1dbeb0) at surface_interface.cpp:400:37 frame #6: 0x00007f9fdfa7164c libKWaylandServer.so.5`KWaylandServer::SurfaceInterface::~SurfaceInterface(this=0x0000560d8c1dbeb0) at surface_interface.cpp:402:1 frame #7: 0x00007f9fdfa70eea libKWaylandServer.so.5`KWaylandServer::SurfaceInterfacePrivate::surface_destroy_resource(this=0x0000560d8c04e910, (null)=0x0000560d8c1fb490) at surface_interface.cpp:295:12 frame #8: 0x00007f9fdfaa2602 libKWaylandServer.so.5`QtWaylandServer::wl_surface::destroy_func(client_resource=0x0000560d8bd7c5e0) at qwayland-server-wayland.cpp:2899:43 frame #9: 0x00007f9fdf92ee90 libwayland-server.so.0`___lldb_unnamed_symbol21$$libwayland-server.so.0 + 96 frame #10: 0x00007f9fdf933851 libwayland-server.so.0`___lldb_unnamed_symbol91$$libwayland-server.so.0 + 65 frame #11: 0x00007f9fdf933d50 libwayland-server.so.0`___lldb_unnamed_symbol101$$libwayland-server.so.0 + 32 frame #12: 0x00007f9fdf92f020 libwayland-server.so.0`wl_client_destroy + 80 frame #13: 0x00007f9fdf92f109 libwayland-server.so.0`___lldb_unnamed_symbol23$$libwayland-server.so.0 + 121 frame #14: 0x00007f9fdf930faa libwayland-server.so.0`wl_event_loop_dispatch + 202 frame #15: 0x00007f9fdf9f1a51 libKWaylandServer.so.5`KWaylandServer::Display::Private::dispatch(this=0x0000560d8ad102d0) at display.cpp:136:31 frame #16: 0x00007f9fdf9f1685 libKWaylandServer.so.5`operator(__closure=0x0000560d8b7704a0) at display.cpp:105:83 frame #17: 0x00007f9fdf9faef0 libKWaylandServer.so.5`QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, KWaylandServer::Display::Private::installSocketNotifier()::<lambda()> >::call(f=0x0000560d8b7704a0, arg=0x00007fffb748d9f0) &, void **) at qobjectdefs_impl.h:146:14 frame #18: 0x00007f9fdf9fa6d7 libKWaylandServer.so.5`QtPrivate::Functor<KWaylandServer::Display::Private::installSocketNotifier()::<lambda()>, 0>::call<QtPrivate::List<>, void>(f=0x0000560d8b7704a0, (null)=0x0000560d8ad100a0, arg=0x00007fffb748d9f0) &, void *, void **) at qobjectdefs_impl.h:256:83 frame #19: 0x00007f9fdf9f8a22 libKWaylandServer.so.5`QtPrivate::QFunctorSlotObject<KWaylandServer::Display::Private::installSocketNotifier()::<lambda()>, 0, QtPrivate::List<>, void>::impl(which=1, this_=0x0000560d8b770490, r=0x0000560d8ad100a0, a=0x00007fffb748d9f0, ret=0x0000000000000000) at qobjectdefs_impl.h:443:49 frame #20: 0x00007f9fdded252f libQt5Core.so.5`QtPrivate::QSlotObjectBase::call(this=0x0000560d8b770490, r=0x0000560d8ad100a0, a=0x00007fffb748d9f0) at qobjectdefs_impl.h:398:57 frame #21: 0x00007f9fddf15778 libQt5Core.so.5`void doActivate<false>(sender=0x0000560d8b6ba760, signal_index=3, argv=0x00007fffb748d9f0) at qobject.cpp:3886:30 frame #22: 0x00007f9fddf0ecd9 libQt5Core.so.5`QMetaObject::activate(sender=0x0000560d8b6ba760, m=0x00007f9fde2b2380, local_signal_index=0, argv=0x00007fffb748d9f0) at qobject.cpp:3946:26 frame #23: 0x00007f9fddf1f530 libQt5Core.so.5`QSocketNotifier::activated(this=0x0000560d8b6ba760, _t1=(sockfd = 7), _t2=Read, _t3=QPrivateSignal @ 0x00007fffb748d9df) at moc_qsocketnotifier.cpp:178:26 frame #24: 0x00007f9fddf1f077 libQt5Core.so.5`QSocketNotifier::event(this=0x0000560d8b6ba760, e=0x00007fffb748df40) at qsocketnotifier.cpp:302:23 frame #25: 0x00007f9fded9fd2b libQt5Widgets.so.5`QApplicationPrivate::notify_helper(this=0x0000560d8acb7340, receiver=0x0000560d8b6ba760, e=0x00007fffb748df40) at qapplication.cpp:3632:31 frame #26: 0x00007f9fded9d069 libQt5Widgets.so.5`QApplication::notify(this=0x00007fffb748e2d0, receiver=0x0000560d8b6ba760, e=0x00007fffb748df40) at qapplication.cpp:2972:31 frame #27: 0x00007f9fddec0255 libQt5Core.so.5`QCoreApplication::notifyInternal2(receiver=0x0000560d8b6ba760, event=0x00007fffb748df40) at qcoreapplication.cpp:1063:24 frame #28: 0x00007f9fddec0cac libQt5Core.so.5`QCoreApplication::sendEvent(receiver=0x0000560d8b6ba760, event=0x00007fffb748df40) at qcoreapplication.cpp:1458:27 frame #29: 0x00007f9fddf520ed libQt5Core.so.5`QEventDispatcherUNIXPrivate::activateSocketNotifiers(this=0x0000560d8acc60d0) at qeventdispatcher_unix.cpp:304:36 frame #30: 0x00007f9fddf52f15 libQt5Core.so.5`QEventDispatcherUNIX::processEvents(this=0x0000560d8accf610, flags=(i = 36)) at qeventdispatcher_unix.cpp:511:50 frame #31: 0x00007f9fd8fb251c KWinQpaPlugin.so`QUnixEventDispatcherQPA::processEvents(this=0x0000560d8accf610, flags=(i = 36)) at qunixeventdispatcher.cpp:63:67 frame #32: 0x00007f9fddebc917 libQt5Core.so.5`QEventLoop::processEvents(this=0x00007fffb748e100, flags=(i = 36)) at qeventloop.cpp:139:68 frame #33: 0x00007f9fddebcc79 libQt5Core.so.5`QEventLoop::exec(this=0x00007fffb748e100, flags=(i = 0)) at qeventloop.cpp:232:22 frame #34: 0x00007f9fddec0aee libQt5Core.so.5`QCoreApplication::exec() at qcoreapplication.cpp:1371:36 frame #35: 0x00007f9fde405184 libQt5Gui.so.5`QGuiApplication::exec() at qguiapplication.cpp:1867:34 frame #36: 0x00007f9fded9ca35 libQt5Widgets.so.5`QApplication::exec() at qapplication.cpp:2824:33 frame #37: 0x0000560d89b5d417 kwin_wayland`main(argc=3, argv=0x00007fffb748e538) at main_wayland.cpp:702:18 frame #38: 0x00007f9fdd542152 libc.so.6`__libc_start_main + 242 frame #39: 0x0000560d89b53c9e kwin_wayland`_start + 46 EXPECTED RESULT No freeze. SOFTWARE/OS VERSIONS KDE Plasma Version: git master KDE Frameworks Version: git master Qt Version: 5.15.2 (built from source code) ADDITIONAL INFORMATION This might be a Qt bug, not sure.
I also got a freeze with that exact trace quite recently! But only once and I couldn't reproduce. If you can reproduce can you print in frame 3: frame #3: print c->receiver It should be the other object that's connected to SurfaceInterface that we're removing the connection for. Given it's a freeze in QAtomicPointer it implies there's some other thread up to no good, but I have no idea what.
Git commit 18df2451de80c72b135b05198da27daa1491eb2c by David Edmundson. Committed on 28/10/2020 at 18:16. Pushed by davidedmundson into branch 'master'. Only connect to BufferInterface::aboutToBeDestroyed once It is allowed to call surface_attach multiple times with the same buffer. We want to only connect once. Found whilst debugging a freeze, going through the list of BufferInterface connections I had multiple to the same SurfaceInterface. M +2 -2 src/server/surface_interface.cpp https://invent.kde.org/plasma/kwayland-server/commit/18df2451de80c72b135b05198da27daa1491eb2c
Git commit 8ab52255442223c5ce43d60f99c8ce8787969120 by David Edmundson. Committed on 28/10/2020 at 18:17. Pushed by davidedmundson into branch 'Plasma/5.20'. Only connect to BufferInterface::aboutToBeDestroyed once It is allowed to call surface_attach multiple times with the same buffer. We want to only connect once. Found whilst debugging a freeze, going through the list of BufferInterface connections I had multiple to the same SurfaceInterface. (cherry picked from commit 18df2451de80c72b135b05198da27daa1491eb2c) M +2 -2 src/server/surface_interface.cpp https://invent.kde.org/plasma/kwayland-server/commit/8ab52255442223c5ce43d60f99c8ce8787969120
Seems like David fixed it