** Description changed: Distribution: Kubuntu 12.04 - Package: qt4-x11 4:4.8.1-0ubuntu4.6 + Package: qt4-x11 4:4.8.1-0ubuntu4.6 Program: LibreOffice 4.3 (current master build). This bugs origin is a crash when using KDE4 native file picker dialogs from within LibreOffice [1]. There are several similar ones in all distributions. In the backtrace you can see, that LO calls the Qt event dispatcher, which processes a draw event, which - at some point - waits for the clipboard using the Qt / LO event loop, which processes another (now nested) draw event -> crash. This happens, because LO sets - qApp->clipboard()->setProperty( "useEventLoopWhenWaiting", true ); + qApp->clipboard()->setProperty( "useEventLoopWhenWaiting", true ); because the X11 event processing in clipboardWaitForEvents would interfere with the LO X11 handling / locking. QX11Data::clipboardWaitForEvents (gui/kernel/qclipboard_x11.cpp:520) actually installs the correct clipboard event filter in the qapp, which should just handle Clipboard events. But actually the Qt internal glib event loop doesn't honor the QEventLoop::ExcludeSocketNotifiers (see src/corelib/kernel/qeventdispatcher_glib.cpp). Originally I opened [2], because I didn't want to deep dive into the Qt codebase. Since I didn't get any usable replies and all my implemented workarounds in LibreOffice didn't work I tried to understand the backtrace from [2] and realized the missing QEventLoop::ExcludeSocketNotifiers handling in the Qt glib code. I opened [3] and pushed a patch for Qt review as [4]. [1] https://bugs.freedesktop.org/show_bug.cgi?id=69002 [2] https://bugreports.qt-project.org/browse/QTBUG-34614 [3] https://bugreports.qt-project.org/browse/QTBUG-37380 [4] https://codereview.qt-project.org/#change,80528 + + [IMPACT] + The patch fixes the glib event loop to pass a currently failing testcase in the Qt4 library (processEventsExcludeSocket in tests/auto/qeventloop/tst_qeventloop.cpp). The flag was never handled in the glib eventloop. + + [TEST CASE] + LibreOffice uses a very rarely used Qt codepath to poll the X11 clipboard (using the event loop), which needs this patch. Otherwise it crashes very often with the KDE 4 backend when polling the clipboard. There is no other codepath. + Test by using LibreOffice with the KDE theme until it crashes. After the patch is applied it will no longer crash. + + [REGRESSION POTENTIAL] + I can't imagine a program out there which relies on this brokeness. + If the patch was really broken to invert the behaviour, the impact would be immediately visible, as no socket events would be processed, including X11 events.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1290514 Title: LibreOffice KDE4 backend crashes in Qt4 recursive paint events To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/qt4-x11/+bug/1290514/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
