unity-2d-shell crashed with SIGSEGV in QCoreApplication::notifyInternal()

I notice only now from the stack trace, that accessibility was probably enabled.

StacktraceTop:
 QCoreApplication::notifyInternal (this=0x7fff3f76f2d0, receiver=0x3ca1480, event=0x7fff3f76e840) at kernel/qcoreapplication.cpp:863
 sendEvent (event=0x7fff3f76e840, receiver=0x3ca1480) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:231
 QAccessible::queryAccessibleInterface (object=0x3ca1480) at accessible/qaccessible.cpp:591
 QAccessible::updateAccessibility (o=<optimized out>, who=0, reason=QAccessible::LocationChanged) at accessible/qaccessible_unix.cpp:102
 QDeclarativeAccessibilityUpdater::sendPostedGeometryUpdates (this=0xa7b100) at util/qdeclarativeaccessibility.cpp:203

Status changed to 'Confirmed' because the bug affects multiple users.

In my case it crash with orca running
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This bug has been reported on the Ubuntu ISO testing tracker.

A list of all reports related to this bug can be found here:
http://iso.qa.ubuntu.com/qatracker/reports/bugs/918707

I'm unable to reproduce with today's Precise. You guys running Oneiric?

I can reproduce on Precise. Ignore above comment.

Status changed to 'Confirmed' because the bug affects multiple users.

I'm unable to reproduce on today's Precise.

I was able to reproduce the same crash by switching lenses in the dash:
1. Enable screen reader (Oraca): System Settings -> Universal Access -> Screen Reader
2. Log out & log in. Verify that QT_ACCESSIBILITY=1 environment variable is set.
3. Close Orca window (probably irrelevant, but that's what I did).
4. Open dash
5. Switch between lenses, repeat until it crashes.

The original recipe with "gconf" search string in the dash doesn't seem to reproduce the problem anymore.

A couple of observations:
1. It seems that the crash occurs only when switching between Video- or Music- lens to any other lens.
2. There are a lot of qt-at-spi warnings related to unsupported events, e.g.
.....
unity-2d-shell: [WARNING] QSpiAccessible::accessibleEvent not handled: "800b" obj: QDeclarativeColumn(0x8c50ba8) ""
unity-2d-shell: [WARNING] QSpiAccessible::accessibleEvent not handled: "800b" obj: TextCustom_QMLTYPE_29(0x902b8b8) ""
unity-2d-shell: [WARNING] QSpiAccessible::accessibleEvent not handled: "800b" obj: TextCustom_QMLTYPE_29(0x90bc010) ""
unity-2d-shell: [WARNING] QSpiAccessible::accessibleEvent not handled: "800b" obj: QDeclarativeItem_QML_60(0x90a9578) ""
unity-2d-shell: [WARNING] QSpiAccessible::accessibleEvent not handled: "800b" obj: QDeclarativeColumn(0x90cf0a8) ""
unity-2d-shell: [WARNING] QSpiAccessible::accessibleEvent not handled: "800b" obj: TextCustom_QMLTYPE_29(0x8ff8718) ""
unity-2d-shell: [WARNING] QSpiAccessible::accessibleEvent not handled: "800b" obj: TextCustom_QMLTYPE_29(0x90d9478) "
......

if you look at stacktrace frame for QDeclarativeAccessibilityUpdater::sendGeometryUpdate method call, its 'item' argument corresponds to one of the QDeclarativeColumn objects displayed in qt-at-spi warnings, e.g.

#6 0xb6e6b163 in QDeclarativeAccessibilityUpdater::sendGeometryUpdate (this=0x81b4c2c, item=0x90cf0a8)

and it's always QDeclarativeColumn for every crash I experienced.

The warning should not be relevant. It just means the bridge ignores some a11y updates. ([WARNING] QSpiAccessible::accessibleEvent not handled)

I had dicussed this problem via email and IRC with Frederik Gladhorn (who implemented a11y changes that we have in kubuntu_97_a11y_qt_and_qml_backport.diff patch) and he blamed geometry/location updates of that patch for the problem. He suggested removal of these pieces of code from the kubuntu_97_a11y_qt_and_qml_backport patch as they are considered as *useless. I've linked a branch that amends this patch - with this change I can no longer reproduce the crash.

Status changed to 'Confirmed' because the bug affects multiple users.

This bug was fixed in the package qt4-x11 - 4:4.8.1-0ubuntu3

---------------
qt4-x11 (4:4.8.1-0ubuntu3) precise; urgency=low

  * kubuntu_97_a11y_qt_and_qml_backport.diff from upstream: removed geometry and animation updates
    because they are useless and the code is buggy, leading to crashes (LP: #918566).
 -- Pawel Stolowski <email address hidden> Mon, 09 Apr 2012 18:55:11 +0200

This bug was fixed in the package unity-2d - 5.10.0-0ubuntu1

---------------
unity-2d (5.10.0-0ubuntu1) precise-proposed; urgency=low

  * New upstream release:
    - unity-2d-shell crashed with SIGSEGV in
      QCoreApplication::notifyInternal() (LP: #918566)
    - Unity-2d-shell crashes on startup on 64bit machines with 20+ tiles in
      launcher (LP: #967012)
    - Unity 2-d launcher doesn't hide or display properly (LP: #940590)
    - [dash] search terms aren't applied on lens change / dash show
      (LP: #947985)
    - [5.8 pre staging] "sticky edge" option does nothing visible
      (LP: #961285)
    - [dash] Maximise, then restore - much of background not removed from
      screen (LP: #968215)
    - [hud] shows up when using ctrl+alt and pressing alt first (LP: #972318)
    - [UIFe] Dash - No message displayed when no results are returned in the
      Dash (LP: #711199)
    - Missing lens shortcuts (Super-A, Super-F) (LP: #834078)
    - [dash] Unable to scroll Filter Results (LP: #920878)
    - [launcher] stays open if you mouseOut before reveal animation completes
      (LP: #943296)
    - HUD on wrong screen on mutli monitor system (LP: #947145)
    - [a11y] Orca reports "Shell" when opening HUD, Dash or Launcher
      (LP: #948033)
    - multimonitor: Please give me a way to turn off sticky monitor edges
      (LP: #946104)
    - [dash] Esc key behavior inconsistent with Unity (LP: #966121)
    - toggling the spread from the launcher does not work (LP: #968146)
    - unity-2d-shell crashed with SIGSEGV in KeyMonitor::registerEvents()
      (LP: #965464)
    - [Dash] Focus is lost when switching with the mouse (LP: #974235)
    - Multiple items selected in HUD list (LP: #948441)
    - Hud hides launcher even if set to always show (LP: #948960)
    - [launcher] Pointer reveal barrier should be 1 way only (LP: #960175)
    - [hud] connection to HUD being created on startup (LP: #965106)
    - [dash] On 1024x786 screen, dash not fullscreen so border truncated
      (LP: #967305)
  * debian/20_ubuntu-2d-gconf-default:
    - set a default key for HUD showing on Alt, in case unity-3d isn't
      installed or run before unity-2d.
  * debian/control:
    - bump libnux-2.0-dev to latest for ABI break
 -- Didier Roche <email address hidden> Thu, 12 Apr 2012 11:02:08 +0200