pcmanfm-qt sigsegv

[agaida]

Expected Behavior

should not crash

Current Behavior

crashes

Possible Solution

fix it

Steps to Reproduce (for bugs)

from Exagone313 in freenode lxqt

<Exagone313> Hi, I have pcmanfm-qt 0.13 and I have reproducible way to make it sigsegv, but I want someone to try out that is NOT using Arch Linux so I know if it's not just about a rebuild needed, I'll create the issue if you can reproduce it.  Open pcmanfm-qt, open a new tab (CTRL+T), open a directory in that second tab, click on the first tab, open a directory in that first tab, click on the second tab => sigsegv.  Here is a gdb backtrace: https://ptpb.pw/6o8u  Thanks

AG: one will notice a repaint bug in the second window - content will not be painted - switching a few times back and forth and it will crash 

crash and backtrace

Thread 1 "pcmanfm-qt" received signal SIGSEGV, Segmentation fault.
Fm::FolderView::folder (this=0x55555592b6c0)
    at /home/agaida/lxqt/libfm-qt-git/src/libfm-qt/src/folderview.h:86
86              return model_ ? static_cast<FolderModel*>(model_->sourceModel())->folder() : nullptr;
(gdb) bt
#0  0x00007ffff74f60bd in Fm::FolderView::folder() const (this=0x55555592b6c0)
    at /home/agaida/lxqt/libfm-qt-git/src/libfm-qt/src/folderview.h:86
#1  0x00007ffff74f60bd in Fm::FolderView::path() (this=0x55555592b6c0)
    at /home/agaida/lxqt/libfm-qt-git/src/libfm-qt/src/folderview.h:95
#2  0x00007ffff74f60bd in Fm::FolderView::onFileClicked(int, std::shared_ptr<Fm::FileInfo const> const&) (this=0x55555592b6c0, fileInfo=std::shared_ptr<const Fm::FileInfo> (empty) = {...}, type=2)
    at /home/agaida/lxqt/libfm-qt-git/src/libfm-qt/src/folderview.cpp:1311
#3  0x00007ffff74f731d in Fm::FolderView::onFileClicked(int, std::shared_ptr<Fm::FileInfo const> const&) (this=0x55555592b6c0, type=<optimized out>, fileInfo=...)
    at /home/agaida/lxqt/libfm-qt-git/src/libfm-qt/src/folderview.cpp:1299
#4  0x0000555555595855 in PCManFM::View::onFileClicked(int, std::shared_ptr<Fm::FileInfo const> const&) (this=0x55555592b6c0, type=<optimized out>, fileInfo=..., this=<optimized out>, fileInfo=..., type=<optimized out>) at /home/agaida/lxqt/pcmanfm-qt-git/src/pcmanfm-qt/pcmanfm/view.cpp:50
#5  0x00007ffff5e03b60 in QMetaObject::activate(QObject*, int, int, void**) ()
    at /usr/lib/libQt5Core.so.5
#6  0x00007ffff754a1a3 in Fm::FolderView::clicked(int, std::shared_ptr<Fm::FileInfo const> const&) (this=this@entry=0x55555592b6c0, _t1=<optimized out>, 
    _t1@entry=2, _t2=std::shared_ptr<const Fm::FileInfo> (empty) = {...})
    at /home/agaida/lxqt/libfm-qt-git/src/build/src/fm-qt_autogen/EWIEGA46WW/moc_folderview.cpp:262
#7  0x00007ffff74f546d in Fm::FolderView::emitClickedAt(Fm::FolderView::ClickType, QPoint const&) (this=this@entry=0x55555592b6c0, type=type@entry=Fm::FolderView::ContextMenuClick, pos=...)
    at /usr/include/c++/8.1.0/bits/shared_ptr_base.h:600
#8  0x00007ffff74f8a37 in Fm::FolderView::contextMenuEvent(QContextMenuEvent*) (this=0x55555592b6c0, event=0x7fffffffd1c0) at /home/agaida/lxqt/libfm-qt-git/src/libfm-qt/src/folderview.cpp:817
#9  0x00007ffff6b89058 in QWidget::event(QEvent*) () at /usr/lib/libQt5Widgets.so.5
#10 0x00007ffff6b49984 in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
    at /usr/lib/libQt5Widgets.so.5
---Type <return> to continue, or q <return> to quit---
#11 0x00007ffff6b51770 in QApplication::notify(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#12 0x00007ffff5dd9bc9 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
    at /usr/lib/libQt5Core.so.5
#13 0x00007ffff6ba4b94 in  () at /usr/lib/libQt5Widgets.so.5
#14 0x00007ffff6ba6fd5 in  () at /usr/lib/libQt5Widgets.so.5
#15 0x00007ffff6b49984 in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
    at /usr/lib/libQt5Widgets.so.5
#16 0x00007ffff6b5125b in QApplication::notify(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#17 0x00007ffff5dd9bc9 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
    at /usr/lib/libQt5Core.so.5
#18 0x00007ffff6381596 in QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent*) () at /usr/lib/libQt5Gui.so.5
#19 0x00007ffff6383516 in QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent*) () at /usr/lib/libQt5Gui.so.5
#20 0x00007ffff635aa5c in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Gui.so.5
#21 0x00007fffecbdbb3d in  () at /usr/lib/libQt5XcbQpa.so.5
#22 0x00007ffff5dd885c in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
    at /usr/lib/libQt5Core.so.5
#23 0x00007ffff5de0b56 in QCoreApplication::exec() () at /usr/lib/libQt5Core.so.5
#24 0x0000555555575b81 in PCManFM::Application::exec() (this=0x7fffffffdcf0)
    at /home/agaida/lxqt/pcmanfm-qt-git/src/pcmanfm-qt/pcmanfm/application.cpp:332
#25 0x0000555555575b81 in main(int, char**) (argc=<optimized out>, argv=<optimized out>)
    at /home/agaida/lxqt/pcmanfm-qt-git/src/pcmanfm-qt/pcmanfm/pcmanfm.cpp:14
(gdb) 

System Information

Arch current, latest git-1 commit

[Exagone313]

Video for reproducing the tab crash (qt5ct NOT concerned, tried also without): https://www.youtube.com/watch?v=dnZsJbFObS0
I don't remember how to reproduce the missing repaint issue.

[agaida]

Reproducing the repaint bug:

 00:09:14 <+agaida> te painting bug - just switch a few times between both tabs and open new directories - after a few switches the content of the switched-to folder will not be painted anymore
 00:09:41 <+agaida> a few switches later the process crashes

[tsujan]

Wow! Strange that I'd never done such a thing! Although I can't reproduce the crash that's reported here, I can see that the second folder isn't painted and pacmanfm-qt crashes after I right-click inside it:

#0  0x00007f187be32c63 in  () at /usr/lib/libfm-qt.so.5
#1  0x00007f187be331ad in Fm::FolderView::onFileClicked(int, std::shared_ptr<Fm::FileInfo const> const&) ()
    at /usr/lib/libfm-qt.so.5
#2  0x0000558ace810216 in  ()
#3  0x00007f187a76fb60 in QMetaObject::activate(QObject*, int, int, void**) () at /usr/lib/libQt5Core.so.5
#4  0x00007f187be59074 in Fm::FolderView::clicked(int, std::shared_ptr<Fm::FileInfo const> const&) ()
    at /usr/lib/libfm-qt.so.5
#5  0x00007f187be8275f in Fm::FolderView::emitClickedAt(Fm::FolderView::ClickType, QPoint const&) ()
    at /usr/lib/libfm-qt.so.5
#6  0x00007f187be827ec in Fm::FolderView::contextMenuEvent(QContextMenuEvent*) () at /usr/lib/libfm-qt.so.5
#7  0x00007f187b4f5058 in QWidget::event(QEvent*) () at /usr/lib/libQt5Widgets.so.5
#8  0x00007f187b4b5984 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#9  0x00007f187b4bd770 in QApplication::notify(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#10 0x00007f187a745bc9 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/libQt5Core.so.5
#11 0x00007f187b510b94 in  () at /usr/lib/libQt5Widgets.so.5
#12 0x00007f187b512fd5 in  () at /usr/lib/libQt5Widgets.so.5
#13 0x00007f187b4b5984 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#14 0x00007f187b4bd25b in QApplication::notify(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#15 0x00007f187a745bc9 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/libQt5Core.so.5
#16 0x00007f187aced596 in QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent*) ()
    at /usr/lib/libQt5Gui.so.5
#17 0x00007f187acef516 in QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent*) () at /usr/lib/libQt5Gui.so.5
#18 0x00007f187acc6a5c in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
    at /usr/lib/libQt5Gui.so.5
#19 0x00007f1871879b3d in  () at /usr/lib/libQt5XcbQpa.so.5
#20 0x00007f187a74485c in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#21 0x00007f187a74cb56 in QCoreApplication::exec() () at /usr/lib/libQt5Core.so.5
#22 0x0000558ace7e6a53 in  ()
#23 0x00007f187c37506b in __libc_start_main () at /usr/lib/libc.so.6
#24 0x0000558ace7e80fa in _start ()

This is very bad. I'll look into it tomorrow.

[tsujan]

@agaida I use Arch's Qt-5.11 too. Can you reproduce this bug under Debian?

[agaida]

it took me several attempts to reproduce this in arch - so just keep clicking - somewhen™ it will not repaint and after a while it will sigsegv - just have to switch to debian and test it there

[tsujan]

OK, this is related to Qt 5.11. I can't reproduce it with Qt 5.10 (on another machine). Damn! In just an hour after I upgraded to Qt 5.11, this is the third problem I encounter (the other 2 aren't related to LXQt and are tolerable).

[tsujan]

Whatever anyone might say, Qt in't backward compatible anymore. grrrrr....

[agaida]

/me knows a distribution with latest LXQt and Qt 5.10 .. - and a default dark design

[tsujan]

To find the cause, I simplify the procedure:

(1) Open 2 windows that show your home.
(2) Go into a subfolder inside one.
(3) Go to another subfolder inside the other.

Then, a miracle will happen and the contents of the first window will be wiped out.

[agaida]

we talk about Qt 5.11? I'm not able to reproduce with Qt 5.10

[tsujan]

we talk about Qt 5.11?

Yes. I found the cause but not the cure yet.

[agaida]

God damn - will it ever be usable before the first or second point release again? :(

[tsujan]

@Exagone313 If possible, test lxqt/libfm-qt#197 with Qt 5.11. It works here.

@agaida Please test the same patch with Qt 5.10.

[Exagone313]

It fixes the issue, yes.

[tsujan]

@Exagone313 Thanks for testing. It was a regression in Qt.

[agaida]

god damn - closing a bug with a commit to my branch is kind of strange