*** Bug 418595 has been marked as a duplicate of this bug. ***

In this report we get to Akonadi::AgentBase::setOnline via a dbus call and the QSettings member is null, hence the crash; the backtrace from bug 418595 comment0 is a bit different code path, but the end result is the same:
Thread 1 (Thread 0x7f83d0b28d80 (LWP 266490)):
[KCrash Handler]
#6  0x00007f83e3a2d5b9 in qGetPtrHelper<QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> > >(QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >&) (ptr=...) at io/qsettings.cpp:3277
#7  QSettings::d_func() (this=<optimized out>) at io/qsettings.h:72
#8  QSettings::setValue(QString const&, QVariant const&) (this=this@entry=0x0, key=..., value=...) at io/qsettings.cpp:3278
#9  0x00007f83e561097e in Akonadi::AgentBase::setOnline(bool) (this=0x7ffc21fe7850, state=state@entry=true) at /tmp/portage/kde-apps/akonadi-19.12.3/work/akonadi-19.12.3/src/agentbase/agentbase.cpp:1032
#10 0x0000564e8a389b84 in ImapResourceBase::onConnectDone(int, QString const&) (this=0x7ffc21fe7850, errorCode=<optimized out>, errorString=...) at /tmp/portage/kde-apps/kdepim-runtime-19.12.3/work/kdepim-runtime-19.12.3/resources/imap/imapresourcebase.cpp:290
#11 0x00007f83e3acf585 in QtPrivate::QSlotObjectBase::call(QObject*, void**) (a=0x7ffc21fe6e80, r=0x7ffc21fe7850, this=0x564e8a8212b0) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:394
#12 doActivate<false>(QObject*, int, void**) (sender=0x564e8a8209e0, signal_index=7, argv=0x7ffc21fe6e80) at kernel/qobject.cpp:3870
#13 0x00007f83e3ac9d47 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) (sender=sender@entry=0x564e8a8209e0, m=m@entry=0x564e8a400200 <SessionPool::staticMetaObject>, local_signal_index=local_signal_index@entry=4, argv=argv@entry=0x7ffc21fe6e80) at kernel/qobject.cpp:3930
#14 0x0000564e8a368d26 in SessionPool::connectDone(int, QString const&) (this=this@entry=0x564e8a8209e0, _t1=<optimized out>, _t1@entry=0, _t2=...) at resources/imap/imapresource_autogen/EWIEGA46WW/moc_sessionpool.cpp:302
#15 0x0000564e8a3bb16e in SessionPool::declareSessionReady(KIMAP::Session*) (this=0x564e8a8209e0, session=<optimized out>) at /usr/include/qt5/QtCore/qarraydata.h:257
#16 0x0000564e8a3bc1c4 in SessionPool::onIdDone(KJob*) (this=0x564e8a8209e0, job=<optimized out>) at /tmp/portage/kde-apps/kdepim-runtime-19.12.3/work/kdepim-runtime-19.12.3/resources/imap/sessionpool.cpp:548
#17 0x00007f83e3acf585 in QtPrivate::QSlotObjectBase::call(QObject*, void**) (a=0x7ffc21fe7060, r=0x564e8a8209e0, this=0x564e8ad49d10) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:394
#18 doActivate<false>(QObject*, int, void**) (sender=0x7f8364012430, signal_index=6, argv=0x7ffc21fe7060) at kernel/qobject.cpp:3870
#19 0x00007f83e4f55b2c in KJob::result(KJob*, KJob::QPrivateSignal) () at /usr/lib64/libKF5CoreAddons.so.5
#20 0x00007f83e4f5662b in KJob::finishJob(bool) () at /usr/lib64/libKF5CoreAddons.so.5
#21 0x00007f83e57a677c in KIMAP::Job::handleErrorReplies(KIMAP::Response const&) () at /usr/lib64/libKF5IMAP.so.5
#22 0x00007f83e57c5d6b in KIMAP::SessionPrivate::responseReceived(KIMAP::Response const&) () at /usr/lib64/libKF5IMAP.so.5
#23 0x00007f83e3ac7a0c in QObject::event(QEvent*) (this=0x564e8ad5fc60, e=0x7f8364042e80) at kernel/qobject.cpp:1339
#24 0x00007f83e46c2eb3 in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=this@entry=0x564e8a59dba0, receiver=receiver@entry=0x564e8ad5fc60, e=e@entry=0x7f8364042e80) at kernel/qapplication.cpp:3684
#25 0x00007f83e46cc3c0 in QApplication::notify(QObject*, QEvent*) (this=0x7ffc21fe7840, receiver=0x564e8ad5fc60, e=0x7f8364042e80) at kernel/qapplication.cpp:3430
#26 0x00007f83e3a9b1ce in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x564e8ad5fc60, event=0x7f8364042e80) at kernel/qcoreapplication.cpp:1092
#27 0x00007f83e3a9ddc7 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) (receiver=0x0, event_type=0, data=0x564e8a57b490) at kernel/qcoreapplication.cpp:1832
#28 0x00007f83e3af1ad3 in postEventSourceDispatch(GSource*, GSourceFunc, gpointer) (s=0x564e8a605740) at kernel/qeventdispatcher_glib.cpp:277
#29 0x00007f83e1ba180f in g_main_context_dispatch () at /usr/lib64/libglib-2.0.so.0
#30 0x00007f83e1ba1bb8 in  () at /usr/lib64/libglib-2.0.so.0
#31 0x00007f83e1ba1c4f in g_main_context_iteration () at /usr/lib64/libglib-2.0.so.0
#32 0x00007f83e3af1880 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x564e8a613d00, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#33 0x00007f83e3a9a01b in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (this=this@entry=0x7ffc21fe7790, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:136
#34 0x00007f83e3aa212f in QCoreApplication::exec() () at ../../include/QtCore/../../src/corelib/global/qflags.h:118
#35 0x00007f83e40638ec in QGuiApplication::exec() () at kernel/qguiapplication.cpp:1866
#36 0x00007f83e46c2e25 in QApplication::exec() () at kernel/qapplication.cpp:2824
#37 0x00007f83e562034e in Akonadi::ResourceBase::init(Akonadi::ResourceBase&) (r=...) at /usr/include/qt5/QtCore/qcoreapplication.h:116
#38 0x0000564e8a355351 in Akonadi::ResourceBase::init<ImapResource>(int, char**) (argc=<optimized out>, argv=<optimized out>) at /usr/include/KF5/AkonadiAgentBase/resourcebase.h:181
#39 0x00007f83e33bce9b in __libc_start_main () at /usr/lib64/libc.so.6
#40 0x0000564e8a352fda in _start () at /tmp/portage/kde-apps/kdepim-runtime-19.12.3/work/kdepim-runtime-19.12.3/resources/imap/main.cpp:22

*** Bug 411089 has been marked as a duplicate of this bug. ***

A possibly relevant merge request was started @ https://invent.kde.org/pim/akonadi/-/merge_requests/24

*** Bug 426090 has been marked as a duplicate of this bug. ***

*** Bug 423557 has been marked as a duplicate of this bug. ***

*** Bug 414404 has been marked as a duplicate of this bug. ***

*** Bug 411378 has been marked as a duplicate of this bug. ***

Git commit 53574eb6fccc8f6a03dcea6c1ca1aa02dd895209 by Ahmad Samir.
Committed on 02/09/2020 at 10:20.
Pushed by ahmadsamir into branch 'master'.

AgentBase: Fix crash in setOnline

When setOnline tries to access the mSettings member after the latter has
been deleted we get a crash; mSettings is deleted in quit() or cleanup(),
therefore it looks like a race condition: the Agent is about to quit, but
some other code calls setOnline leading to a crash. It looks like this can
happen in more than one way, e.g. via a dbus call (from AgentInstance), or
via a sub-class of AgentBase calling setOnline directly. Use a bool member
var, modelled after how AgentInstance uses a similar logic.

M  +8    -0    src/agentbase/agentbase.cpp
M  +2    -0    src/agentbase/agentbase_p.h

https://invent.kde.org/pim/akonadi/commit/53574eb6fccc8f6a03dcea6c1ca1aa02dd895209

(In reply to Ahmad Samir from comment #9)
> Git commit 53574eb6fccc8f6a03dcea6c1ca1aa02dd895209 by Ahmad Samir.
> Committed on 02/09/2020 at 10:20.
> Pushed by ahmadsamir into branch 'master'.
> 
> AgentBase: Fix crash in setOnline

Can/will this this be backported to 20.04 and 20.08?

Git commit 66d1135d127331fb3a2a7e047b0577d7e67d3dc2 by Ahmad Samir.
Committed on 02/09/2020 at 10:58.
Pushed by ahmadsamir into branch 'release/20.08'.

AgentBase: Fix crash in setOnline

When setOnline tries to access the mSettings member after the latter has
been deleted we get a crash; mSettings is deleted in quit() or cleanup(),
therefore it looks like a race condition: the Agent is about to quit, but
some other code calls setOnline leading to a crash. It looks like this can
happen in more than one way, e.g. via a dbus call (from AgentInstance), or
via a sub-class of AgentBase calling setOnline directly. Use a bool member
var, modelled after how AgentInstance uses a similar logic.
(cherry picked from commit 53574eb6fccc8f6a03dcea6c1ca1aa02dd895209)

M  +8    -0    src/agentbase/agentbase.cpp
M  +2    -0    src/agentbase/agentbase_p.h

https://invent.kde.org/pim/akonadi/commit/66d1135d127331fb3a2a7e047b0577d7e67d3dc2

I asked and I was told that release/20.04 is closed since 20.08 was released. So we don't push commits to the old stable branch.

(Of course you can file a bug report in your distro bugzilla and a package maintainer can backport the fix manually, I think it should apply cleanly).

Thanks for the reminder about pushing to release/20.08 o/

Still crashes.

Application: akonadi_imap_resource (5.15.2 (20.08.2))

Qt Version: 5.15.1
Frameworks Version: 5.75.0
Operating System: Linux 5.8.14-1-default x86_64
Windowing system: X11
Distribution: openSUSE Tumbleweed

Thread 1 (Thread 0x7eff3da35080 (LWP 1847)):
[KCrash Handler]
#4  0x00007eff4e21a8ca in QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::operator-> (this=<optimized out>) at io/qsettings.cpp:3270
#5  qGetPtrHelper<QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> > > (ptr=...) at ../../include/QtCore/../../src/corelib/global/qglobal.h:1135
#6  QSettings::d_func (this=<optimized out>) at io/qsettings.h:72
#7  QSettings::setValue (this=this@entry=0x0, key=..., value=...) at io/qsettings.cpp:3271
#8  0x00007eff4fcc41bd in Akonadi::AgentBase::setOnline (this=0x7ffed6d18a10, state=false) at /usr/include/qt5/QtCore/qstring.h:962

As of today, 2020-12-09, the issue is no longer reproducible on my Fedora 33 system with:
* kf5-akonadi-server-20.08.3-1.fc33
* kf5-pimcommon-akonadi-20.08.3-1.fc33

*** Bug 442157 has been marked as a duplicate of this bug. ***

Created attachment 141376 [details]
New crash information added by DrKonqi

akonadi_imap_resource (5.18.0 (21.08.0)) using Qt 5.15.2

I have all the same issues on akonadi 21.08.0 (Well, I have it for years already, and it happens time to time, I just decided to report it only now).

I also redy to bet that it will keep happening on .1 too

-- Backtrace (Reduced):
#4  0x00007fe085898069 in QSettings::setValue(QString const&, QVariant const&) () at /usr/lib64/libQt5Core.so.5
#5  0x00007fe0872206fd in Akonadi::AgentBase::setOnline(bool) () at /usr/lib64/libKF5AkonadiAgentBase.so.5
#6  0x000055e0b6ff2252 in ImapResourceBase::configure(unsigned long long) ()
#7  0x00007fe08724af43 in Akonadi__ControlAdaptor::qt_metacall(QMetaObject::Call, int, void**) () at /usr/lib64/libKF5AkonadiAgentBase.so.5
#8  0x00007fe085bdd669 in QDBusConnectionPrivate::deliverCall(QObject*, int, QDBusMessage const&, QVector<int> const&, int) () at /usr/lib64/libQt5DBus.so.5

Created attachment 147620 [details]
New crash information added by DrKonqi

akonadi_imap_resource (5.18.3 (21.08.3)) using Qt 5.15.2

- What I was doing when the application crashed:
Trying to toggle online/offline from unclear online/offline state (empty info in akonadiconsole)

-- Backtrace (Reduced):
#4  0x00007b0237569399 in QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::operator->() const (this=<optimized out>) at ../../include/QtCore/../../../qtbase-f4ac0b55c37f2b594ffbe639db43dac365825c7c/src/corelib/tools/qscopedpointer.h:118
[...]
#7  QSettings::setValue(QString const&, QVariant const&) (this=this@entry=0x0, key=..., value=...) at /var/tmp/portage/dev-qt/qtcore-5.15.2-r14/work/qtbase-f4ac0b55c37f2b594ffbe639db43dac365825c7c/src/corelib/io/qsettings.cpp:3271
#8  0x00007b0238ff955d in Akonadi::AgentBase::setOnline(bool) (this=0x7ffef3c29750, state=false) at /var/tmp/portage/kde-apps/akonadi-21.08.3/work/akonadi-21.08.3/src/agentbase/agentbase.cpp:1003
#9  0x00007b023902598d in Akonadi__StatusAdaptor::setOnline(bool) (state=<optimized out>, this=<optimized out>) at /var/tmp/portage/kde-apps/akonadi-21.08.3/work/akonadi-21.08.3_build/src/agentbase/statusadaptor.cpp:51
#10 0x00007b0239025c43 in Akonadi__StatusAdaptor::qt_metacall(QMetaObject::Call, int, void**) (this=0x5f49ac78b510, _c=QMetaObject::InvokeMetaMethod, _id=8, _a=0x7ffef3c29110) at /var/tmp/portage/kde-apps/akonadi-21.08.3/work/akonadi-21.08.3_build/src/agentbase/statusadaptor.moc:238

Created attachment 151247 [details]
New crash information added by DrKonqi

akonadi_imap_resource (5.20.3 (22.04.3)) using Qt 5.15.5

- What I was doing when the application crashed:
Trying to restart an IMAP instance that had not visible state (empty instead of ‘Ready’ or something like that)

-- Backtrace (Reduced):
#4  0x00007322192f4c99 in QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::operator->() const (this=<optimized out>) at /var/tmp/portage/dev-qt/qtcore-5.15.5-r2/work/qtbase-everywhere-src-5.15.5/include/QtCore/../../src/corelib/tools/qscopedpointer.h:118
[...]
#7  QSettings::setValue(QString const&, QVariant const&) (this=this@entry=0x0, key=..., value=...) at /var/tmp/portage/dev-qt/qtcore-5.15.5-r2/work/qtbase-everywhere-src-5.15.5/src/corelib/io/qsettings.cpp:3271
#8  0x000073221ac3f4dd in Akonadi::AgentBase::setOnline(bool) (this=0x7ffc706bf100, state=true) at /var/tmp/portage/kde-apps/akonadi-22.04.3/work/akonadi-22.04.3/src/agentbase/agentbase.cpp:1000
#9  0x00005e0fec677404 in ImapResourceBase::onConnectDone(int, QString const&) (this=0x7ffc706bf100, errorCode=<optimized out>, errorString=<optimized out>) at /var/tmp/portage/kde-apps/kdepim-runtime-22.04.3/work/kdepim-runtime-22.04.3/resources/imap/imapresourcebase.cpp:271
#10 0x0000732219394e86 in QtPrivate::QSlotObjectBase::call(QObject*, void**) (a=0x7ffc706be990, r=0x7ffc706bf100, this=0x5e0fed94c350) at /var/tmp/portage/dev-qt/qtcore-5.15.5-r2/work/qtbase-everywhere-src-5.15.5/include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398

Created attachment 153106 [details]
New crash information added by DrKonqi

akonadi_imap_resource (5.21.2 (22.08.2)) using Qt 5.15.6

i was changing settings within kontact settings and it seemed to crash unexpectedly

-- Backtrace (Reduced):
#4  0x00007fac6dbc671a in QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::operator->() const (this=<optimized out>) at ../../include/QtCore/../../src/corelib/tools/qscopedpointer.h:118
[...]
#7  QSettings::setValue(QString const&, QVariant const&) (this=0x0, key=..., value=...) at io/qsettings.cpp:3271
#8  0x00007fac6f66fb75 in Akonadi::AgentBase::setOnline(bool) () at /lib64/libKF5AkonadiAgentBase.so.5
#9  0x0000560d5d32f34c in ImapResourceBase::onConnectDone(int, QString const&) (this=0x7ffe14ad2860, errorCode=<optimized out>, errorString=<optimized out>) at /usr/src/debug/kdepim-runtime-22.08.2-1.1.x86_64/resources/imap/imapresourcebase.cpp:271
#10 0x00007fac6dc8205d in QtPrivate::QSlotObjectBase::call(QObject*, void**) (a=0x7ffe14ad2070, r=0x7ffe14ad2860, this=0x560d5eac1b30) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398