Bug 430945

SUMMARY

When using a 'hotcorner' to initiate 'present windows', windows present correctly but then using the hotcorner again to exit 'present windows', kwin often crashes.

Note that triggering 'present windows' with keyboard shortcut does NOT result in a crash.

STEPS TO REPRODUCE
1. Configure top-right hotcorner as 'present windows'
2. Repeatedly hit top-right corner of screen
3. Observe entering and exiting of 'present windows'

OBSERVED RESULT

After a few tries, kwin will crash with SIGSEGV.

EXPECTED RESULT

System should enter and exit 'present windows' repeatedly without issue.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kubuntu 20.10
(available in About System)
KDE Plasma Version: 5.19.5
KDE Frameworks Version: 5.74.0
Qt Version: 5.14.2
Kernel: 5.8.0-33-generic

ADDITIONAL INFORMATION

Cannot be sure but the issue _seems_ easier to reproduce when windows have no title bars (disabled with 'Hide Window Borders' keyboard shortcut (shift-alt-f9)).

Backtrace:
Application: KWin (kwin_x11), signal: Segmentation fault

[KCrash Handler]
#4  0x00007f24986794ee in KWin::Workspace::workspaceEvent(xcb_generic_event_t*) () at /lib/x86_64-linux-gnu/libkwin.so.5
#5  0x00007f24972f14ef in QAbstractEventDispatcher::filterNativeEvent(QByteArray const&, void*, long*) () at /lib/x86_64-linux-gnu/libQt5Core.so.5
#6  0x00007f2491033505 in QXcbConnection::handleXcbEvent(xcb_generic_event_t*) () at /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#7  0x00007f2491034a46 in QXcbConnection::processXcbEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#8  0x00007f2491057740 in  () at /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#9  0x00007f24972f2a4b in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /lib/x86_64-linux-gnu/libQt5Core.so.5
#10 0x00007f24972fafc6 in QCoreApplication::exec() () at /lib/x86_64-linux-gnu/libQt5Core.so.5
#11 0x000055a3320caa6d in  ()
#12 0x00007f2496c7acb2 in __libc_start_main (main=0x55a3320ca6a0, argc=3, argv=0x7fff24a130e8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fff24a130d8) at ../csu/libc-start.c:314
#13 0x000055a3320caf8e in _start ()
[Inferior 1 (process 27214) detached]