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Rare crash on showing context menu of notification area item #1802

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tsujan opened this issue Jul 27, 2022 · 7 comments · May be fixed by lxqt/libdbusmenu-lxqt#17
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Rare crash on showing context menu of notification area item #1802

tsujan opened this issue Jul 27, 2022 · 7 comments · May be fixed by lxqt/libdbusmenu-lxqt#17
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@tsujan
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tsujan commented Jul 27, 2022 •
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On rare occasions, for which only the single example of nm-applet --indicator is found until now, lxqt-panel may crash on showing the context menu inside the notification area.

nm-applet's original menu is problematic (→ https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/502), and the cause of the crash is in Qt, not in lxqt-panel:

#0  0x00007fd52eb12ba4 in  () at /usr/lib/libQt5Widgets.so.5
lxqt/lxqt-notificationd#1  0x00007fd52eb17d06 in QMenu::internalDelayedPopup() () at /usr/lib/libQt5Widgets.so.5
lxqt/lxqt-notificationd#2  0x00007fd52deee07f in QObject::event(QEvent*) () at /usr/lib/libQt5Core.so.5
lxqt/lxqt-notificationd#3  0x00007fd52e994762 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
lxqt/lxqt-notificationd#4  0x00007fd52dec163a in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/libQt5Core.so.5
lxqt/lxqt-notificationd#5  0x00007fd52df194c5 in QTimerInfoList::activateTimers() () at /usr/lib/libQt5Core.so.5
lxqt/lxqt-notificationd#6  0x00007fd52df19d72 in  () at /usr/lib/libQt5Core.so.5
lxqt/lxqt-notificationd#7  0x00007fd52d6cd02c in g_main_context_dispatch () at /usr/lib/libglib-2.0.so.0
lxqt/lxqt-notificationd#8  0x00007fd52d720b59 in  () at /usr/lib/libglib-2.0.so.0
lxqt/lxqt-notificationd#9  0x00007fd52d6ca781 in g_main_context_iteration () at /usr/lib/libglib-2.0.so.0
lxqt/lxqt-notificationd#10 0x00007fd52df1a141 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
    at /usr/lib/libQt5Core.so.5
lxqt/lxqt-notificationd#11 0x00007fd52debff9c in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
lxqt/lxqt-notificationd#12 0x00007fd52dec8454 in QCoreApplication::exec() () at /usr/lib/libQt5Core.so.5
lxqt/lxqt-notificationd#13 0x00005595dbbd40b7 in  ()
lxqt/lxqt-notificationd#14 0x00007fd52d888b25 in __libc_start_main () at /usr/lib/libc.so.6
lxqt/lxqt-notificationd#15 0x00005595dbbd468e in _start ()

Apparently, the crash happens in the private slot QMenu::internalDelayedPopup().

I opened this issue in the hope that a workaround might be found.

System Information
  • Latest git LXQt
@tsujan tsujan added the Qt bug label Jul 27, 2022
@tsujan tsujan transferred this issue from lxqt/lxqt-notificationd Jul 27, 2022
@tsujan tsujan changed the title Rare crash on showing context menu Rare crash on showing context menu of notification area item Jul 27, 2022
@tsujan tsujan mentioned this issue Jul 27, 2022
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@tsujan
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tsujan commented Jul 27, 2022

May be somehow related to https://bugreports.qt.io/browse/QTBUG-77273

@tsujan tsujan mentioned this issue Jan 11, 2024
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Still an issue?

@tsujan
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tsujan commented Mar 16, 2024

Still an issue?

I haven't checked, but since the Qt bug report is still unresolved, the issue should still exist. Fortunately, it's very rare.

I wonder if a workaround is possible in libdbusmenu-lxqt.

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tsujan commented Apr 23, 2024

I can't reproduce the issue with Qt6 lxqt-panel + the latest nm-applet + Wayland (labwc). I think something has changed in nm-applet.

Since it wasn't our bug, closing...

@tsujan tsujan closed this as completed Apr 23, 2024
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tsujan commented May 22, 2024 •
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It happened again with nm-applet --indicator but with a different backtrace for Qt6:

#0  0x00007f31c1b010c8 in QAction::isSeparator() const () at /usr/lib/libQt6Gui.so.6
#1  0x00007f31c22c275c in ??? () at /usr/lib/libQt6Widgets.so.6
#2  0x00007f31c22cb132 in QMenu::timerEvent(QTimerEvent*) () at /usr/lib/libQt6Widgets.so.6
#3  0x00007f31c118c0e6 in QObject::event(QEvent*) () at /usr/lib/libQt6Core.so.6
#4  0x00007f31c20fc44d in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/libQt6Widgets.so.6
#5  0x00007f31c113fe18 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/libQt6Core.so.6
#6  0x00007f31c12b7988 in QTimerInfoList::activateTimers() () at /usr/lib/libQt6Core.so.6
#7  0x00007f31c13957c9 in ??? () at /usr/lib/libQt6Core.so.6
#8  0x00007f31c0f0ea89 in ??? () at /usr/lib/libglib-2.0.so.0
#9  0x00007f31c0f709b7 in ??? () at /usr/lib/libglib-2.0.so.0
#10 0x00007f31c0f0df95 in g_main_context_iteration () at /usr/lib/libglib-2.0.so.0
#11 0x00007f31c1393389 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
    at /usr/lib/libQt6Core.so.6
#12 0x00007f31c1148350 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt6Core.so.6
#13 0x00007f31c1143c1d in QCoreApplication::exec() () at /usr/lib/libQt6Core.so.6
#14 0x0000562c3bbfe2ea in ??? ()
#15 0x00007f31c0a39c88 in ??? () at /usr/lib/libc.so.6
#16 0x00007f31c0a39d4c in __libc_start_main () at /usr/lib/libc.so.6
#17 0x0000562c3bbfeb75 in _start ()

EDIT: This time it happened under LXQt+LabWC. Qt's version is 6.7.0.

@tsujan tsujan reopened this May 22, 2024
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tsujan commented May 22, 2024

Sorry, I reopened it by mistake. Still not our bug.

@tsujan tsujan closed this as completed May 22, 2024
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tsujan commented Nov 9, 2024 •
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I think I've found a workaround for this Qt bug, which persists in Qt6. I'll make a PR against libdbusmenu-lxqt if I can't reproduce the crash with the workaround for a day or two (the crash was very easy to reproduce with nm-applet).

Reopening...

EDIT: After I wrestled with it for many hours, it crashed again. I really tried many ways — even borrowed KDE codes —to no avail.

EDIT2: Found an effective workaround at last.

@tsujan tsujan reopened this Nov 9, 2024
tsujan added a commit to lxqt/libdbusmenu-lxqt that referenced this issue Nov 15, 2024
@tsujan
Workaround for a Qt crash on reloading menus
3ec1d83 
Such random crashes are triggered by Qt → `QMenu::timerEvent()`. Qt doesn't take into account the possibility of dangling pointers in `qmenu.cpp` under very rare circumstances, e.g., when the actions of a menu with a visible submenu are recreated too rapidly multiple times (also see https://bugreports.qt.io/browse/QTBUG-77273, although our case is much more complex). That may no be unexpected in a code full of timers and event handling.

To avoid dangling pointers, the patch just puts a minimum interval of two seconds between two consecutive reloads.

It also restores the active action on refreshing, such that a reloaded submenu isn't closed anymore (see lxqt/lxqt#2282 and especially @yan12125's report https://gitlab.gnome.org/GNOME/network-manager-applet/-/issues/195).

Finally, it removes a redundant, recursive computation.

Closes lxqt/lxqt-panel#1802

NOTE: I was able to reproduce the crash easily with nm-applet. Before arriving at this workaround, I tried various ideas but could still make lxqt-panel crash in a few minutes. Only this time I can't, in spite of trying for days.
@tsujan tsujan linked a pull request Nov 15, 2024 that will close this issue
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Workaround for a Qt crash on reloading menus lxqt/libdbusmenu-lxqt
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