cursor interactions cause lockup with pocket desktop

[Kevin DuBois]

To reproduce (seen on frieza):

Connect a mouse to a pocket desktop setup.
Launch a 'legacy' application, like gedit, in windowed mode. The problem is not seen with 'native' applications, it seems that the setting the custom cursor bitmap that Xmir does is the precipitating event for the problem.
Rapidly move the cursor over the edge of the window to force rapid cursor transitions.
After a while (usually between 30s-2 minutes of the rapid movement), the desktop will lock up.

First noted on mir 0.23 testing (silo 69), but also seen with 0.22.1.

USC is still alive, and doesn't look locked up. Unity8 is locked.

Render logs from Qt for the last 2 frames (including the one that's locked)
http://pastebin.ubuntu.com/16953202/

BT of threads when attaching to unity8 when stuck:
http://pastebin.ubuntu.com/16952340/
note: it seems that thread 1 is the render loop, and thread 2 is the render thread. Thread 2 doesn't quite seem stuck (seems to be busy, and doesnt unblock), and thread 1 is stuck waiting for a response from thread 2

If I disable the notification of the cursor change callback in mir (just commenting out here)
http://bazaar.launchpad.net/~mir-team/mir/0.22/view/head:/src/server/scene/basic_surface.cpp#L693
This breaks the cursor updating for Xmir apps, but averts the crash

[Kevin DuBois (kdub)]

not quite sure if its a mir problem or a qtmir+u8 problem, so will tag both.

[Daniel d'Andrada (dandrader)]

Steps for pocked desktop setup:
https://docs.google.com/document/d/1gfLy7cBHHwZXD0t74tqYpHvw60W5nc_qJoYUiU4A6mo/edit#

[Kevin DuBois (kdub)]

Package versions of qtmir+u8+mirserver, as well as the system-image-cli. (installed on frieza)

[Kevin DuBois (kdub)]

I noticed this first during mir 0.23.0 release testing... so wanted to see if it was a the race was any better or worse with 0.23.0 vs 0.22.1.

So, did a quick manual check of time to failure on 0.23.0 and 0.22.1. (attached). Seems its just about as prevalent on each version of mir. This doesn't exonerate mir altogether, but IMO, should let us proceed with the 0.23.0 release.

[Daniel van Vugt (vanvugt)]

There is a known bug where libmirclient crashes on Xmir cursor updates -> bug 1506358
Please check your Xmir has not crashed (so this bug is not a duplicate of that one)

If this was bug 1506358 though I would expect Unity8 to keep working and not freeze the whole desktop. But Unity8 might not be able to survive bug 1506358 as well as the Mir demo servers(?).

Please also check Unity8 lockup bug 1588534

[Kevin DuBois (kdub)]

Xmir does not appear to have crashed. I don't think this is bug 1506358, as that exception isn't seen, and it appears to be the Qt renderloop/renderthread that is locked up.

[Daniel d'Andrada (dandrader)]

Cause seems to be a busy loop in QQuickSpriteEngine::assembledImage() triggered by changing between bitmap cursors (as opposed to named cursors).

[Daniel d'Andrada (dandrader)]

It's a but in Qt triggered by the peculiar way unity8 uses AnimatedSprite QML Type

[Daniel d'Andrada (dandrader)]

s/but/bug

[Daniel d'Andrada (dandrader)]

Qt bug:
https://bugreports.qt.io/browse/QTBUG-53937

[Daniel d'Andrada (dandrader)]

Fix for bug in qtdeclarative:
https://codereview.qt-project.org/#/c/161896/

[Launchpad Janitor (janitor)]

This bug was fixed in the package unity8 - 8.12+16.10.20160617-0ubuntu1

---------------
unity8 (8.12+16.10.20160617-0ubuntu1) yakkety; urgency=medium

  [ Michael Terry ]
  * Do not create Label/Icon if we don't need it
  * Fix Z-ordering of prompt surfaces (LP: #1586219)
  * Drop bottom edge tutorials completely and small fixes for other
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  * Redo visuals for greeter prompt box. (LP: #1435923)
  * Make tutorial qmltests more robust. (LP: #1590810)
  * Stop showing an extra lockscreen in desktop unity8 sessions. (LP:
    #1582987)

  [ Albert Astals Cid ]
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  * Stabilize PreviewExpandableTest::test_all_widgets_height
  * Workaround QTBUG-53460
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  * Tests: Do not use dynamic_cast if we're not going to test it anyway
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  * Make wait in cleanup() wait for snapTo animation to have finished

  [ Alexandros Frantzis ]
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  [ Andrea Cimitan ]
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  * Same tweaks we have for click scope now for libertine
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  [ Daniel d'Andrada ]
  * Clean up debug leftovers
  * Ensure mouse and window movement are pixel-aligned (LP: #1510382)
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  * No point in version-controlling files that are automatically
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  * Center cursor on screen when it's first shown
  * Custom cursor name just have to start with "custom"
  * Work around AnimatedSprite infinite loop bug (LP: #1588929)

  [ Josh Arenson ]
  * Disable showDash when it is already shown. (LP: #1506708)
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  * Add timestamp to unity8 log (LP: #1498169)

  [ Lukáš Tinkl ]
  * Implement keyboard shortcuts info panel
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  [ Michael Zanetti ]
  * Add support for the launcher surface pips displaying the correct
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    completely and invoking it later (LP: #1565236)

  [ Stephen M. Webb ]
  * added a new upstart $SESSION for unity8-desktop-session (LP:
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 -- Michael Terry <email address hidden> Fri, 17 Jun 2016 01:22:57 +0000