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Help in locating source of Qt 5.6.0 assertion crash



  • I have reported a crash when running browser examples in Qt 5.6.0 on Ubuntu 14.04.
    The report is here ..

    https://forum.qt.io/topic/65459/qtwebenginewidgets-example-crash-report

    But no replies so far.
    Can anyone help to troubleshoot this pattern in Qt Creator Application Output
    ../../nouveau/pushbuf.c:726: nouveau_pushbuf_data: Assertion `kref' failed.
    which appears just before the crash occurs?

    So far in searching around I've found a few bug reports (google search the above pattern) .. but no solution.



  • I have really hit a dead end with this Assertion `kref' failed report which I see when running Qt 5.6.0 example demobrowser.

    In Qt 5.6 Creator I tried starting a Debug session

    (1) Loaded project demobrowser into Qt Creator

    (2) Debug > Start Debugging

    (3) demobrowser builds with debug information seen.

    (4) Popup message box at end ...

    The inferior stopped because it received a signal from the operating system.

    Signal name : SIGABRT
    Signal meaning : Aborted

    (5) Looking at Qt Creator debug information panels

    Disassembler refers to __kernel_vsyscall
    Threads refers to #22 Chrome InProcGP Stopped: Aborted (Signal SIGABRT)

    (6) The full debugger dump is pasted into pastebin guest account

    http://pastebin.com/gi07NLQU

    The summary is seen at line 931 ...

    demobrowser: ../../nouveau/pushbuf.c:726: nouveau_pushbuf_data: Assertion `kref' failed.

    (7) I cannot decipher debug dumps so I'm hoping that some experienced developer can offer a clue on how to troubleshoot this crash.

    It seems to point to nouveau/mesa. But I'm guessing.


  • Lifetime Qt Champion

    Hi,

    Looks like something lower level between web engine and nouveau. You should try to contact both of them folks.

    You might also want to bring that to the QtWebEngine mailing list You'll find there QtWebengine developers/maintainers. This forum is more user oriented.



  • @SGaist

    Thanks for that tip. I'll head to that mailing list to research further.

    I did find today a few users who report similar problems with QtWebEngine.

    Here is one .. http://thankcoder.com/questions/k1xxt/qtwebengine-demo-application-crashes



  • SOLVED

    I picked up a clue from the owner of the PPA repo.

    The problem was in an open source NVIDIA driver I had installed. X.Org.
    This was seen in Ubuntu Software Centre > Software Sources > Additional Drivers
    I dropped to another NVIDIA driver (proprietary, tested).

    http://askubuntu.com/questions/498401/installing-nvidia-drivers-to-14-04

    Rebooted.

    I was able to run Qt 5.6.0 demobrowser without hitting previous nouveau crash.

    I may have to try different proprierary drivers but moving away from X.Org open source driver has removed the crash conditions.


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