Review Request 127261: Fix dead lock when program use kauth exits.

[Xuetian Weng]

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This is an automatically generated e-mail. To reply, visit:
https://git.reviewboard.kde.org/r/127261/
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(Updated March 2, 2016, 8:58 p.m.)


Review request for KDE Frameworks and David Edmundson.


Repository: kauth


Description (updated)
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I'm on Qt 5.6 RC, and just notice a issue that kded5 never cleanly exits.

With gdb attached to kded5, it shows following backtrace:

    #1  0x00007ffff5c820eb in QWaitConditionPrivate::wait (time=18446744073709551615, this=0x74ac70) at thread/qwaitcondition_unix.cpp:136
    #2  QWaitCondition::wait (this=this at entry=0x71c308, mutex=mutex at entry=0x71c300, time=time at entry=18446744073709551615) at thread/qwaitcondition_unix.cpp:208
    #3  0x00007ffff5c7b08b in QSemaphore::acquire (this=this at entry=0x7fffffffd840, n=n at entry=1) at thread/qsemaphore.cpp:137
    #4  0x00007ffff5e80fff in QMetaObject::activate (sender=sender at entry=0x976280, signalOffset=<optimized out>, local_signal_index=local_signal_index at entry=0, argv=argv at entry=0x7fffffffd8d0)
        at kernel/qobject.cpp:3698
    #5  0x00007ffff5e81687 in QMetaObject::activate (sender=sender at entry=0x976280, m=m at entry=0x7ffff6092760 <QObject::staticMetaObject>, local_signal_index=local_signal_index at entry=0, 
        argv=argv at entry=0x7fffffffd8d0) at kernel/qobject.cpp:3595
    #6  0x00007ffff5e8172f in QObject::destroyed (this=this at entry=0x976280, _t1=_t1 at entry=0x976280) at .moc/moc_qobject.cpp:213
    #7  0x00007ffff5e886e5 in QObject::~QObject (this=<optimized out>, __in_chrg=<optimized out>) at kernel/qobject.cpp:913
    #8  0x00007fffb39bbb09 in KAuth::DBusHelperProxy::~DBusHelperProxy (this=0x976280, __in_chrg=<optimized out>) at /chakra/core/kauth/src/kauth-5.19.0/src/backends/dbus/DBusHelperProxy.cpp:55
    #9  0x00007ffff5e49ff9 in QLibraryPrivate::unload (this=0x71dba0, flag=QLibraryPrivate::NoUnloadSys) at plugin/qlibrary.cpp:551
    #10 0x00007ffff5e4e521 in QLibraryStore::cleanup () at plugin/qlibrary.cpp:397
    #11 0x00007ffff78592ef in __cxa_finalize () from /usr/lib/libc.so.6
    #12 0x00007ffff5c52583 in __do_global_dtors_aux () from /usr/lib/libQt5Core.so.5
    #13 0x00007fffffffe230 in ?? ()
    #14 0x00007ffff7dea867 in _dl_fini () from /lib64/ld-linux-x86-64.so.2


Which indicates that kauth dbus plugin's QObject::destroyed is being connected to QDBusConnectionPrivate with Qt::BlockQueuedConnection. But at this point, QApplication is already gone and this call is never being handled. Disconnect everything in destructor can fix this issue.

Related upstream qt code:
https://github.com/qtproject/qtbase/blob/5.6.0/src/dbus/qdbusintegrator.cpp#L2135


Diffs
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  src/backends/dbus/DBusHelperProxy.cpp 20dad0a 

Diff: https://git.reviewboard.kde.org/r/127261/diff/


Testing
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Now kded5 can exits upon logout/exit. Tested with kquitapp5 kded5.


Thanks,

Xuetian Weng

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