[Kde-hardware-devel] Review Request: resolve deadlock on app exit in fstab backend

[Mario Bensi]

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sorry about this problem.
The problem here, it's the QFileSystemWatcher must be deleted before Q[Core]Application, your solution is good but i think the QFileSystemWatcher is leaked when you detach this from the parent. I send another patch which complete your solution.
Thanks for your help.

- Mario


On 2010-08-31 01:09:50, Aaron Seigo wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> http://reviewboard.kde.org/r/5193/
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> 
> (Updated 2010-08-31 01:09:50)
> 
> 
> Review request for Solid.
> 
> 
> Summary
> -------
> 
> we're seeing this hang on Solid-using apps on application exit:
> 
> #0  0xffffe424 in __kernel_vsyscall ()
> #1  0xb5e9b125 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
> #2  0xb5f28f69 in QWaitConditionPrivate::wait (this=0x84116d8, time=4294967295)
>     at /home/aseigo/kde4/qt/src/corelib/thread/qwaitcondition_unix.cpp:88
> #3  0xb5f28d6d in QWaitCondition::wait (this=0x8428190, mutex=0x8428178, time=4294967295)
>     at /home/aseigo/kde4/qt/src/corelib/thread/qwaitcondition_unix.cpp:160
> #4  0xb5f2864e in QThread::wait (this=0x83bfac8, time=4294967295)
>     at /home/aseigo/kde4/qt/src/corelib/thread/qthread_unix.cpp:660
> #5  0xb6004859 in QFileSystemWatcher::~QFileSystemWatcher (this=0x8411200, 
>     __in_chrg=<value optimized out>) at /home/aseigo/kde4/qt/src/corelib/io/qfilesystemwatcher.cpp:440
> #6  0xb60049ad in QFileSystemWatcher::~QFileSystemWatcher (this=0x8411200, 
>     __in_chrg=<value optimized out>) at /home/aseigo/kde4/qt/src/corelib/io/qfilesystemwatcher.cpp:456
> #7  0xb6049478 in QObjectPrivate::deleteChildren (this=0x83c0d70)
>     at /home/aseigo/kde4/qt/src/corelib/kernel/qobject.cpp:1949
> #8  0xb6047d44 in QObject::~QObject (this=0x83c1618, __in_chrg=<value optimized out>)
>     at /home/aseigo/kde4/qt/src/corelib/kernel/qobject.cpp:945
> #9  0xb4e883ea in Solid::Ifaces::DeviceManager::~DeviceManager (this=0x83c1618, 
>     __in_chrg=<value optimized out>)
>     at /home/aseigo/kde4/KDE/kdelibs/solid/solid/ifaces/devicemanager.cpp:29
> #10 0xb4ece7a1 in Solid::Backends::Fstab::FstabManager::~FstabManager (this=0x83c1618, 
>     __in_chrg=<value optimized out>)
>     at /home/aseigo/kde4/KDE/kdelibs/solid/solid/backends/fstab/fstabmanager.cpp:132
> #11 0xb4ece7db in Solid::Backends::Fstab::FstabManager::~FstabManager (this=0x83c1618, 
>     __in_chrg=<value optimized out>)
>     at /home/aseigo/kde4/KDE/kdelibs/solid/solid/backends/fstab/fstabmanager.cpp:134
> #12 0xb4e70430 in qDeleteAll<QList<QObject*>::const_iterator> (begin=..., end=...)
>     at /home/aseigo/kde4/qt-copy/include/QtCore/qalgorithms.h:322
> #13 0xb4e702d9 in qDeleteAll<QList<QObject*> > (c=...)
>     at /home/aseigo/kde4/qt-copy/include/QtCore/qalgorithms.h:330
> #14 0xb4e6fe8d in Solid::ManagerBasePrivate::~ManagerBasePrivate (this=0x8416c58, 
>     __in_chrg=<value optimized out>) at /home/aseigo/kde4/KDE/kdelibs/solid/solid/managerbase.cpp:47
> #15 0xb4e72f72 in Solid::DeviceManagerPrivate::~DeviceManagerPrivate (this=0x8416c50, 
>     __in_chrg=<value optimized out>) at /home/aseigo/kde4/KDE/kdelibs/solid/solid/devicemanager.cpp:48
> #16 0xb4e72fc1 in Solid::DeviceManagerPrivate::~DeviceManagerPrivate (this=0x8416c50, 
>     __in_chrg=<value optimized out>) at /home/aseigo/kde4/KDE/kdelibs/solid/solid/devicemanager.cpp:62
> #17 0xb4e763f2 in QThreadStorage<Solid::DeviceManagerPrivate*>::deleteData (x=0x8416c50)
>     at /home/aseigo/kde4/qt-copy/include/QtCore/qthreadstorage.h:133
> #18 0xb5f26466 in QThreadStorageData::finish (p=0x80528d8)
>     at /home/aseigo/kde4/qt/src/corelib/thread/qthreadstorage.cpp:185
> #19 0xb6030be6 in QCoreApplicationPrivate::~QCoreApplicationPrivate (this=0x8079940, 
>     __in_chrg=<value optimized out>)
>     at /home/aseigo/kde4/qt/src/corelib/kernel/qcoreapplication.cpp:291
> #20 0xb53a446b in QApplicationPrivate::~QApplicationPrivate (this=0x8079940, 
> 
> it's hanging in a call to QInotifyFileSystemWatcherEngine::wait(), which is actually a call to QThread::wait(). on my laptop, this results in the process not exiting fully, a spike in CPU usage that slowly (over the course of several minutes) comes down to ~1% of the CPU. the spike happens increasingly quickly, and the spin down takes increasingly long as it approaches 0, which is probably a clue. :) 
> 
> as can be seen in the backtrace, QThreadStorageData::finish is being called, which results in Solid being destroyed, which results in the QThread-based QFileSystemWatcherEngine going into a wait mode ... deadlock.
> 
> this patch, while certainly not "pretty", does the job.
> 
> 
> This addresses bug 249557.
>     https://bugs.kde.org/show_bug.cgi?id=249557
> 
> 
> Diffs
> -----
> 
>   /trunk/KDE/kdelibs/solid/solid/backends/fstab/fstabmanager.h 1170183 
>   /trunk/KDE/kdelibs/solid/solid/backends/fstab/fstabmanager.cpp 1170183 
> 
> Diff: http://reviewboard.kde.org/r/5193/diff
> 
> 
> Testing
> -------
> 
> run plasma-desktop, try kquitapp plasma-desktop and ensure it exits cleanly.
> 
> 
> Thanks,
> 
> Aaron
> 
>

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