Created attachment 1152069 [details]
/var/log/messages

Created attachment 1152070 [details]
journal

So the system isn't really hung, it's more like it's at a desktop but just not showing most things. KDE is definitely *there*. If I hit the power button, the "Logging out" stripe appears, for e.g. If I move the mouse to the top-left corner of the screen, I see the blue glow. Clicking where the kicker should be doesn't make it visible, though.

This is far from a fresh problem. Earliest mention I can find that I made anywhere is https://bugzilla.redhat.com/show_bug.cgi?id=1283348#c33 but I know I didn't mention until some number of weeks after first seeing it. I just booted multiboot host gx27b's F24 to update, after last having been updated 9 weeks ago, and it did exactly as I described there. I was able to open apps via Alt-F2, but until then, and the inevitable segfault window, the only GUI activity I saw were mouse pointer and brief startup splash screen. After dnf update, black screen/missing panel behavior is unchanged, but a segfault window does not materialize.

it appears plasmashell process may be deadlocked, getting a backtrace from it may be helpful

Happened the same to me.

Fedora i386 Live KDE

Fedora-KDE-Live-i386-24-20160522.n.0.iso
After boot shows just black screen.

Yup, yet another problem on my i686 (x86_64 unaffected).

Gnome works fine, but when I try to log into KDE, I get the pretty starfield and the nice progress bar, all swift and clean, and then...

nothing!

OK, just reproduced it on my box.

As suspected (by me), it's dying down in /lib/sse2/libQt5ml.so.5 in QV4:: routines, apparently related to memory management

(transcribing)

#0 ... in ?? ()
#1 ... in QV4::PersistentValueStorage::mark(QV4::ExecuationEngine*) ...
#2 ... in QV4::MemoryManager::mark() ...
#3 ... in QV4::MemoryManager::runGC() ...
#4 ... in QV4::MemoryManager::allocData(unsigned int, unsigned int) ...
#5 ... in QV4::ExecuationEngine::newVariantObject(QVariant const&) ...

For giggles, moved the sse2 one out of the way to force use of /lib/libQt5Qml.so.5, and get an (apparent) identical backtrace.

Looks like a dup of similar/same issue in bug #1329715 (currently assigned to sddm), but it's clearly both lower-level in qt5-qtdeclarative

Is this bug what I'm seeing on i686 F24 host gx280, using startx in multi-user.target?

# rpmqa kactiv
kactivities-libs-4.13.3-20.fc24.i686
kactivitymanagerd-5.6.4-1.fc24.i686
kf5-kactivities-libs-5.22.0-1.fc24.i686
kf5-kactivities-stats-5.22.0-1.fc24.i686
# rpm -qa | grep ^qt
qt-4.8.7-17.fc24.i686
...
qt5-qtdeclarative-5.6.0-5.fc24.i686
...
[  149.727392] traps: plasmashell[1328] general protection ip:ab6df4cd sp:bfcd1be8 error:502
[  362.029952] kactivitymanage[1221]: segfault at b0b52b4c ip af1c5ccc sp bfa8010c error 4 in libQt5Sql.so.5.6.0[af1b3000+48000]
[  454.716529] traps: plasmashell[1801] general protection ip:ab6694ae sp:bfb7556c error:c6a0
[  489.654786] kactivitymanage[1700]: segfault at b0b15b4c ip b01c7ccc sp bf8149bc error 4 in libQt5Sql.so.5.6.0[b01b5000+48000]
[  727.423430] kactivitymanage[2084]: segfault at b0b11b4c ip ae779ccc sp bfcd990c error 4 in libQt5Sql.so.5.6.0[ae767000+48000]
[ 4827.296710] kactivitymanage[2510]: segfault at b0b57b4c ip b01c7ccc sp bfaa3b7c error 4 in libQt5Sql.so.5.6.0[b01b5000+48000]
[ 6152.646571] systemsettings5[3173]: segfault at 0 ip   (null) sp bfa2278c error 4 in systemsettings5[80042000+1a000]

I'm able to get Konsole to open via a quick Alt-F2 after splash went away, but not if I wait.

OK, after a bit of discussion, kde-sig highly suspected this is a qt5-qtdeclarative issue, most likely triggered by gcc6.

So, installed f24/i686 workstation, and installed @kde-desktop-environment on top of that to do additional testing, and found that building qt5-qtdeclarative with addtional flag: -fno-lifetime-dse , seemed to fix the crashes for me.

Here's a build that includes that for testing purposes:
http://koji.fedoraproject.org/koji/taskinfo?taskID=14291923

*** This bug has been marked as a duplicate of bug 1329715 ***